A Comprehensive Sampling of the Hell Creek Formation

[ThePhysicist]

Introduction

 

The Hell Creek Formation (HCF) is a geologic unit deposited during the Maastrichtian of the Late Cretaceous (ca. 66 million years ago) in North America, recording the last page in the chronicle of non-avian dinosaurs. It represents a paleo-ecosystem that hosted some of the most charismatic animals ever, including T. rex, Triceratops, and others. While its dinosaurs certainly deserve attention, the HCF was burgeoning with overshadowed diversity. A large dinosaur skeleton provides an excellent picture of a single animal, but it alone tells us very little about its world. By looking at small fossils, (“microfossils”) en masse, we can open a larger window into the past, and better appreciate that fuller diversity of life.

 

Over the past year I’ve been on a meticulous campaign, searching through a copious volume of HCF matrix collected on private land in Montana. So far, I’ve amassed a comprehensive collection of nearly four dozen distinct species from thousands of cm-micron scale fossils that span the whole fauna, including mollusks, bony and cartilaginous fishes, crocodyliforms, turtles, salamanders, frogs, lizards, mammals, and of course dinosaurs. In this thread I will detail my initial findings, and provide updates as I find new things. I’ve gotten a lot of joy in discovering, learning about, and documenting these fossils; hopefully this reading will similarly be an enjoyable venture into the Late Cretaceous, and be helpful to fellow micro-hunters.

 

A family of Triceratops at the bank of a river channel. Art by Donna Braginetz.

 

Collage of microfossils and silhouettes, a sampling of a few of the animals present in this complex community (not to scale).

 

Below is a working faunal list of animals I have yet found, in not-so-formal categories in no particular order. In making my identifications, I’ve used a myriad of resources from peer reviewed literature, books, Dr. Dave DeMar’s ID guide, etc. It’s fortunate for me that the HCF is very well studied and published on - it’s been collected and researched intensely for over a century. I will cite the respective resources where appropriate (please pardon any inconsistent or incorrect formatting, I simply don’t have the patience for this non-academic work). I also provide a rough sketch of identification for some fossils that is in no way wholistic, but should suffice for most amateurs. And as always, I welcome informed corrections. 

 

Click on an underlined group to skip to that section.

 

Invertebrates:

Gastropoda cf. Viviparus 

Lioplacodes tenuicarinata

Unionoidea indet. 

Sphaerium beckmani

 

Plants:

Carbonized plant matter & amber

Wodehousia spinata (palynomorph)

 

Osteichthyes (Bony Fishes):

Lepisosteidae (Lepisosteus occidentalis) 

Cyclurus fragosus 

Holostei indet.

Teleostei indet.

Perciformes cf. Priscacara

Estesesox sp.

Acanthomorhpa type HC-2

Acipenser “erucifer”

 

Chondrichthyes (Cartilaginous Fishes):

Myledaphus pustulosus 

Lonchidion selachos 

Restesia americana

Galagadon nordquistae

 

Lissamphibia (Amphibians):

Anura indet.

Urodela indet.

?Habrosaurus sp.

?Scapherpeton tectum

 

Non-dinosaurian reptiles:

Crocodyliformes indet.

Brachychampsa montana

Champsosaurus sp.

Trionychidae indet.

Basilemys sp.

Varanoidea indet.

Polyglyphanodontia indet.

 

Mammalia (Mammals):

Metatheria indet.

Multituberculata indet.

?Meniscoessus robustus

Mesodma sp.

Cimolodon sp.

Gypsonictops sp.

 

Dinosauria:

 

Ornithischia:

Ceratopsidae cf. Triceratops

Leptoceratops gracilis

Edmontosaurus annectens

Nodosauridae cf. Denversaurus

Thescelosaurus sp.

Pachycephalosauridae

Ornithischia indet.

 

Saurischia (Theropoda):

Zapsalis abradens (=Dromaeosauridae)

Richardoestesia isosceles

?Richardoestesia gilmorei

Paronychodon sp.

?Ornithomimidae

Theropoda indet.

Acheroraptor temertyorum

Dromaeosauridae indet.

Pectinodon bakkeri

Tyrannosaurus rex

 

I have also roughly been keeping track of the quantity and diversity of specimens to have some crude statistical sense of the deposit’s demographics. There is some ambiguity here in how I’m counting fossils (e.g. a jaw with teeth and an isolated tooth are each counted as one), however I don’t have the time to figure out a better way to keep track, and anyhow the purpose of this is just to provide a ballpark summary. There is also unrealized diversity, since I couldn’t identify some fossils very precisely. Keep in mind there are significant preservation and human biases here, so these charts don’t accurately reflect the true abundance of animals in the environment, merely the relative quantities of fossils I recovered.

 

By quantity of identifiable fossils, the deposit was dominated by fishes, namely Myledaphus. Following in abundance were ornithischian dinosaurs and non-dinosaur reptiles. Osteichthyes is also undercounted since I get tired of counting broken scales and shed Cylcurus teeth (keep in mind at this point I’ve had to record many hundreds of specimens).

 

 

I also considered the relative abundance of dinosaurs. Following the results of many other studies, hadrosaurid and ceratopsid fossils were quite common compared to theropods. The rarest dinosaurs represented were the ankylosaurians. Of course since e.g. ornithomimids and oviraptorosaurs lacked teeth or small identifiable parts, they are under-represented. 

 

Digression on Lithology and Taphonomy

 

Geology is a crucial tool for understanding these fossils and how they were preserved; in the interest of providing greater context, I will offer some brief comments on the rock these fossils were found in and their taphonomy (how they were fossilized). 

 

The host rock these fossils come from is a loose sandstone conglomerate. It was deposited by an ancient river channel, like many HCF deposits. These river channels laced through forested floodplains and swamps, draining into the receding Western Interior Seaway that cut through the middle of North America during the Late Cretaceous. They carried within them a load of sediment sourced from the then-nascent Rocky Mountains in the West. Gill & Cobban (1973) found that the sediment specifically came from the volcanic Elkhorn mountains region. 

 

The river was likely freshwater and further inland with little to no marine influence (discussed later). It’s possibly a so-called lag deposit, where sediment settled out of the current on the inside of a river bend, where the slower flow allows material to drop out and accumulate in a small volume. The disaggregated matrix itself is about half sand/silt and half claystone/ironstone pebbles by volume, the pebbles being ~ cm’s in size, the largest about 10 cm. The claystone pebbles are essentially rip-up mud clasts, where high currents in the river eroded pre-existing mud and transported it some distance downstream. Most have rounded forms and easily fracture, revealing a very fine-grained interior. The geology of the ironstone pebbles I’m less confident about; they are either preformed, part of the river’s load and secondarily deposited, or are diagenetic, forming after deposition of the sediment (or both - clarification would be appreciated). They similarly have rounded forms, but are very solid and more dense; when broken they show their concretionary structure. Also present are typically small (< 1 cm), river-polished, extra-formational metamorphic pebbles - persevering fragments of the Rockies not yet ground to sand. The matrix is inundated with pulverized fragments of iridescent unionoid mussel shells. Following in abundance are bone fragments, and lastly are identifiable vertebrate fossils. I estimate the vertebrate fossil volumetric yield to be less than 1-2% (including unidentifiable bone fragments), similar to Rogers & Brady (2010). However, as you’ll see, that seemingly minimal yield has produced spectacular diversity.

 

Map of North America ca. 66 million years ago, showing the approximate location of the deposit in the context of its paleo-geography. Rivers transported sediment from the young Rockies in the West to the receding seaway in the East. Map adapted from Tyler Carpenter.

 

Sediment accumulation in the Williston basin during the Late Cretaceous (Gill & Cobban 1973). Roughly following the gradient of the contours (a right angle to the tangent of the lines) gives the direction of sediment transport. These data support the sediment of the HCF coming specifically from the volcanic Elkhorn mountains region.

 

The Elkhorn mountains viewed from the north. It is in part thanks to these mountains that we have fossils of Judithian/Lancian dinosaurs in Montana.

 

Unprocessed matrix. There’s nothing apparently special upon first glance; just sand, pebbles, and shell slivers

 

 

Wetting the matrix reveals the darker fossil bones.

 

Typical claystone pebbles - essentially mud balls that were rolled by the river current. Getting an idea of the size distribution of these pebbles might say something about the speed of the river’s flow, a task for a later date.

 

Various mud clasts

 

Mudstone pebbles with unidentifiable plant matter. The leftmost chunk has an orange piece of amber visible.

 

Many planty mudstone pebbles show laminations (fine layers) and cleave in planes, indicating they preserve the original sedimentation undisturbed by river action. The foremost portion of the left piece may preserve a seed.

 

Metamorphic pebbles, looks like mostly quartzite? These pebbles look the same as they did 66 million years ago.

 

Sand with flecks of mica and mollusk shell. The rare remaining vertebrate fossils at this scale are mere crumbs of bone that aren’t worth collecting.

 

Channel deposits are particularly valuable microsites since they can capture a large cross section of the fauna and concentrate fossils into a small volume, still there are biases to be considered. For example, larger fossils are often broken up in the current, only fossils of a certain size range are captured, and more durable fossils are favored for preservation, while fragile ones are more commonly destroyed. Teeth and scales are both strongly selected for in this mode of preservation; as we’ll see they make up a large portion of the finds. Because this rock was once an active river, many fossils show signs of significant water transport and chemical corrosion pre-fossilization (as is typical of channel-hosted microsites, see Rogers & Brady 2010). Physical weathering erases detail and smooths sharp features, chemical weathering dissolves the bone and leaves shallow pitting on the surface. Some bones are heavily tumbled into rounded forms (some are nearly polished) and are referred to as “bone pebbles” in the literature. Most smaller bones show greater degree of tumbling, which makes intuitive sense, since they could be carried farther down the river before settling out. Much of the material here is from aquatic life, which is natural for a river deposit. The terrestrial material would’ve found its way to the river due to rains and flooding washing things in, or say if an animal died or otherwise directly deposited material in the river (e.g. a dromaeosaurid shedding a tooth while feeding on a carcass on the riverbank).

 

Now, there is some dispute as to the true origins of many of these microsite bone beds. Rogers & Brady 2010 proposed that channel-hosted microsites actually sourced their fossils by eroding pre-existing lacustrine (lake) deposits. They claim this scenario explains the similar quality of preservation and rich diversity in both kinds of deposits. It’s an interesting idea, but I don’t know enough about sedimentology to contest it or test it.

 

All of the material here was deeply buried and only recently exhumed last Summer (after ca. 66 million years of waiting) near the HCF type locality, so there is little environmental degradation like sun bleaching or plant root etching. All of the bones are chocolate browns in color, some nearly black. The quality of preservation varies substantially, from heavily corroded and worn to incredibly pristine. Most fossils I find are just chunks of bone, but every once in a while something more substantial pops out.

 

The vast majority of what I find looks like this - chunks of bone and fish bits. In leaving “no stone unturned”, I’ve picked out thousands of pieces of this stuff just to recover a handful of exquisite specimens.

 

A sampling of unidentifiable bone fragments, ranging from cm-mm in size

 

Well-tumbled “bone pebbles”; I have an odd appreciation for these rounded and smoothed bits of bone. Some might’ve gone on long journeys to get so smooth.

 

Pitting on the surface of bone, evidence of pre-fossilization corrosion. 

 

Illustration of channel weathering effects: physical and chemical. A) Trionychid turtle shell; B) holostean fish (Cyclurus) maxilla.

 

Fastovsky, David E. and Antoine Bercovici. “The Hell Creek Formation and its contribution to the Cretaceous–Paleogene extinction: A short primer.” Cretaceous Research 57 (2016): 368-390.

 

Rogers, Raymond R., and Mara E. Brady. "Origins of Microfossil Bonebeds: Insights from the Upper Cretaceous Judith River Formation of North-central Montana." Paleobiology 36.1 (2010): 80-112.

 

Gill, J. R. and William Aubrey Cobban. “Stratigraphy and geologic history of the Montana group and equivalent rocks, Montana, Wyoming, and North and South Dakota.” (1973).

 

Processing Methods

 

I knew I wanted to search this matrix as thoroughly as humanly possible; my goal was to recover every single fossil hidden within it. Though experienced at searching matrix, I’m by no means professional or optimal when it comes to processing. The goal of preparing matrix is to make fossils easier to find. You want to remove as much rock as possible to concentrate the fossils, and for ease of searching, you want to separate fossils by size. This is usually done with metal screens, which accomplish both. I follow the method of “screen washing” practiced by paleontologists for over a century - simply running water over matrix on screens of varying mesh sizes. As we all know, water is excellent for separating things like dirt and rock because it’s a polar molecule, and it I think better mediates collisions between objects during screening so delicate fossils are less likely to break. As mentioned earlier, roughly half the volume is sand, so a good deal of “fossil-empty” matrix can be easily winnowed out this way. 

 

For screens to wash the matrix through, I used food strainers of a couple different sizes from the local grocery store. I caught the sediment that fell through with cut up old plastic jugs sitting in cheap storage tubs to catch overflow. It’s not ideal, but it’s cheap and it works. Very few fossils were broken, and my yield is maxed out - the two things that matter most. (You check yield by looking at the finest grain size and make sure there’s nothing left in it.)

At the cm scale, I searched through the clay pebbles by eye under good lighting against a white background to maximize contrast, and I picked out particularly cool or delicate fossils I managed to spot as I washed the matrix. It helped that when wet, the fossils were dark brown-black and stood out from the lighter matrix. At the mm-scale, I used a binocular microscope with 20x magnification, sorting through a spoonful of material at a time with a small paintbrush.

 

I always enjoy seeing “as found” pics, so here are a few,

 

That was a good day - a large Edmontosaurus dentary tooth

 

99 times out of 100, the small shiny triangular thing is a fish scale, the other time it’s a troodontid tooth - as in this case

 

Mammals are always a joy to find - a rooted marsupial lower premolar

 

A salamander caudal vertebra in association with a fragment of amiid fish palate

 

An uncommon microscopic carpet shark tooth - Galagadon nordquistae - just a mm or two in size

 

A marsupial upper premolar, hiding among mollusk shell flakes

 

Now, on to what I actually found!

Edited May 26 by ThePhysicist

[ThePhysicist]

Invertebrates & Plants

 

Far from the most popular HCF fossils to collect, invertebrates and plants however are crucial members of the ecosystem. I’ve so far only found fossils of mollusks and plants, I doubt I’ll ever find insects - it’s not the right depositional environment.

 

Unionoidea (freshwater mussels)

 

Mussel shell fragments litter the matrix, so much so that even in the finest grain size it looks to have been laced with glitter. The original shell material that makes them appear iridescent (nacre) is preserved, which makes it somewhat surreal to sort through - as if this dirt was shoveled from a river yesterday. The colors are more vibrant when they’re damp. Unfortunately they are extremely fragile and crumble if you so much as look at them. Below are some of the more intact specimens. Many pieces show evidence of extended river transport and are tumbled into pebbles. 

 

These mussels are often called “Unio” in the literature, the same superfamily of mussels populates rivers of North America today. They burrow themselves in soft sandy riverbeds, straining the current for food. They were a crucial component of the fauna, cleaning the water, and were likely a source of food for many animals in this ecosystem (e.g. Myledaphus). They are quite commonly reported in Cretaceous channel deposits, and their shells comprised a fair portion of the rivers’ load. Many of my specimens compare well with Pleurobema cryptorhynchus, but I wouldn’t stake anything on it since they’re so incomplete, and I so unfamiliar with mollusks.

 

Unionoid fragment, showing iridescence

 

A collection of more complete unionoids, most of their outer layer has been stripped

 

Shells tumbled into pebbles

 

Oops.

 

Henning & Hartman 2007

 

Scholz, Henning, and Joseph H. Hartman. “Paleoenvironmental Reconstruction of the Upper Cretaceous Hell Creek Formation of the Williston Basin, Montana, USA: Implications from the Quantitative Analysis of Unionoid Bivalve Taxonomic Diversity and Morphologic Disparity.” PALAIOS, vol. 22, no. 1, 2007, pp. 24–34. JSTOR, http://www.jstor.org/stable/27670392. 

 

Loris S. Russell. 1976. Pelecypods of the Hell Creek Formation (Uppermost Cretaceous) of Garfield County, Montana. Canadian Journal of Earth Sciences. 13(2): 365-388. https://doi.org/10.1139/e76-039

 

 

Sphaerium beckmani (pea clams)

 

Another group of freshwater bivalves present are pea clams. Like their bigger cousins the unionoids, they filter fed, burrowing in the sandy riverbed. This genus is extant. They are extremely fragile, so I’ve opted to leave the sand in place. 

 

Identification: their shells are thin and very fragile. They are small (usually < 1 cm in size) and have an oval shape. 

 

A pod(?) of pea clams

 

Perhaps not the most enlightening graphic with all the sand obscuring… geologic compression has pressed sand grains in the exterior surface and essentially erased what little surface detail their was, and I’ve left sand in the the internal surface for support.

 

Russell 1976

 

Loris S. Russell. 1976. Pelecypods of the Hell Creek Formation (Uppermost Cretaceous) of Garfield County, Montana. Canadian Journal of Earth Sciences. 13(2): 365-388. https://doi.org/10.1139/e76-039

 

Gastropoda (snails)

 

Much less common and often overlooked are snails. The larger ones are typically preserved as mudstone internal casts, the smaller ones are mm-scale and do preserve the aragonite shell. Most are fragmentary as the unionoids are, but I did find a remarkably complete one. I did not find many publications on HCF gastropods, but similar steinkerns from the Horseshoe Canyon Formation (early Maastrichtian) have been identified as Viviparus sp. 

 

Internal casts of larger gastropod steinkerns, ?Viviparus sp.

 

Larson et al. 2010

 

Smaller gastropods, ~ 1-2 mm in size, though they could be part of a larger shell as below

 

A exquisitely well-preserved snail - note the three ridges which flow with the spiral. The original aragonite shell is ever so rarely this complete.

 

Slide by Mike Bangle-Davis

 

D.W. Larson, D.B. Brinkman, and P.R. Bell. (2010) “Faunal assemblages from the upper Horseshoe Canyon Formation, an early Maastrichtian cool-climate assemblage from Alberta, with special reference to the Albertosaurus sarcophagus bonebed.” Canadian Journal of Earth Sciences. 47(9): 1159-1181. https://doi.org/10.1139/E10-005

 

Meek, F. B.; Hayden, F. V. (1857). Descriptions of new genera of fossils, collected by Dr. F.V. Hayden, in Nebraska territory, under the direction of Lieut. G.K. Warren, US Topographical Engineer; with some remarks on the Tertiary and Cretaceous formations of the north-west, and parallelism of the latter with those of other portions of the United States and Territories. Proceedings of the Academy of Natural Sciences of Philadelphia. 9: 117–148., available online at https://www.biodiversitylibrary.org/page/6330383

page(s): 137-138

 

Plant Matter & Amber

 

Plants are a cornerstone of many terrestrial ecosystems, so I was pleased to have found a few plant fossils. Plant material is uncommon in general, but I found it to be more common in samples with more abundant mud clasts. Many mud clasts themselves preserved plant matter within them (see above). The most common macroscopic plant fossils were carbonized wood. These splinters of essentially charcoal preserve the original tissue structure and have been interpreted as evidence that forest fires were common in the HCF. I have also found a couple of pieces of amber, they were associated with carbonized plant material, and fluoresce under black light. 

 

A few pieces of carbonized plant material

 

Broken carbonized plant material showing transportive tissue structures preserved

 

Poorly-preserved orange amber within carbonaceous material

 

More familiar resinous amber (mm-sized)

 

A hadrosaurid watches a forest fire. Art by Hank Sharpe.

 

Fastovsky, David E. and Antoine Bercovici. “The Hell Creek Formation and its contribution to the Cretaceous–Paleogene extinction: A short primer.” Cretaceous Research 57 (2016): 368-390.

 

Seeds

 

Remember the claystone pebbles I talked about? Some of these clasts are rich in planty debris. I took a closer look at some of them recently and began finding several small seeds! Some are preserved as 3D mud casts with a carbonaceous “shell”, others are flattened but seem to preserve the waxy seed coat/cuticle. Since this is a recent discovery, I don’t know much about what I’m finding - a subject for a future update.

 

A small (1-2 mm) seed still in its claystone pebble matrix.

 

Pollen Grains (Palynomorphs)

 

Pollen/spores are reproductive structures produced in most plants, they are microscopic (typically measured in microns, 0.001 mm) and vary in size/shape by species. For many people, they are the worst part of Spring, triggering runny noses and itchy eyes. But for curious paleontologists, they are a most useful tool; in fact they were the first indicator of an abrupt change across the K-Pg boundary. Pollen are very informative, useful for determining a rock’s age (as index fossils), and for telling us what kinds of plants were around without finding more substantial remains; a single stone can carry the vestiges of an entire forest. 

 

Certainly pollen was the most difficult fossil to find. Pollen require entirely different processing techniques to extract them from rock without destroying them, concentrate them, avoid modern contamination (though modern taxa may be recognized), and find. I only recently considered trying to extract them, mostly just to see if I could (I did stop to think if I should). I can detail my process if folks are interested, but I believe I was so inefficient and shoddy that there’s little education in expounding. This exercise was largely a proof of principle, done with things lying around the house (solo cups, ceramic plant saucer, stove, hydrogen peroxide). In any case, I was successful in recovering pollen, and happy to add another branch to this already expansive undertaking. 

 

Similar to eggs, pollen/spores are classified using form taxa (palynomorphs), and may not necessarily be attributable to known organismal taxa. Thus far, I’ve only confidently found one taxon, and it will likely remain that way for the foreseeable future since it’s currently an intensive, low-reward endeavor. I am stowing away plenty of what appears to be palynomorph-rich material for the future.

 

Wodehousia spinata

 

A palynomorph taxon, likely from an angiosperm (flowering plant). They are reportedly very common in the HCF and must have been an important component of the flora. They did survive the K-Pg extinction event, though they eventually died out and left no living descendants. This is the first palynomorph I confidently identified due to their unique structure that was obviously not a rock. This species also defines an assemblage zone, and confirms that we’re in the Upper Maastrichtian.

 

Identification: “This morphologically unique species is tetraporate with two pores on each hemisphere of the ovate lenticular body of the grain; it has a prominent, presumably equatorial flange supported by spines, and scattered, echinate sculpture.” (Nichols 2002)

 

Now that’s a microfossil, viewed at 250x magnification with cropping; it’s likely about 50 microns (0.05 mm) in size. This by far is the smallest fossil I’ve ever found. Interestingly, it’s flattened like a coin due to geologic compression. It hasn’t been stained, it indeed appeared to have a yellowish color.

 

Nichols 2002

 

Nichols, D.J., 2002, Palynology and palynostratigraphy of the Hell Creek Formation in North Dakota: A microfossil record of plants at the end of Cretaceous time, in Hartman, J.H., Johnson, K.R., and Nichols, D.J., eds., The Hell Creek Formation and the Cretaceous-Tertiary boundary in the northern Great Plains: An integrated continental record of the end of the Cretaceous: Boulder, Colorado, Geological Society of America Special Paper 361, p. 393–456. 

 

Edited May 26 by ThePhysicist

[ThePhysicist]

Osteichthyes (bony fishes)

 

Bony fishes are an important component of this ecosystem, and as expected, are well-represented in a riverine deposit. They were quite diverse, something my IDs don’t fully capture. Curiously, I’ve yet to find Melvius which is a commonly-reported amiid.

Lepisosteidae (Lepisosteus occidentalis)

 

A gar fish, whose genus is still with us today (though some publications refrain from identifying this fish beyond the family level). They are heavily armored predatory fish with long snouts bristling with needle-like teeth. One of the most common fossils in the matrix were gar scales. Since they are thin, the scales break easily, but I managed to find a handful that were in good condition. Other possible fossils are ornamented skull bones, jaws, teeth, and vertebrae. Fishing as a child in Texas, I was startled when I saw a gar for the first time - it came to the surface for a gulp of air next to my bobber, brandishing its sharp teeth with a hiss - these fossil gar scare me less.

 

Identification: Gar scales are generally diamond-shaped and possess a hard, shiny enamel-like tissue on the outer surface, “ganoine.” Their vertebrae are “opisthocoelous” - anterior cotyle is convex, posterior cotyle is concave, which distinguishes them from other fish here. Their teeth are small, erect and conical, with a translucent acrodin cap and ridges running the length of the tooth up to the acrodin; there are no carinae unlike the similar teeth of Champsosaurus. 

 

Lepisosteid ganoid scales

 

Various gar elements. A) vertebra in ventral and anterior views; B) enlarged view of an actinopterygian tooth, presumably lepisosteid; C) ornamented skull bones (may be from another holostean); D) dentary fragment in lateral and occlusal views, note the double tooth rows, teeth unassociated.

 

Modern spotted gar. Photo by Joel Sartore. 

 

Szabó, M., Gulyás, P., and Ősi, A. 2016. Late Cretaceous (Santonian) Atractosteus (Actinopterygii, Lepisosteidae) remains from Hungary (Iharkút, Bakony Mountains). Cretaceous Research 60: 239–252. 

 

DeMar, D.G. “An Illustrated Guide to latest Cretaceous Vertebrate Microfossils of the Hell Creek Formation of northeastern Montana.” Unpublished. https://naturalhistory.si.edu/sites/default/files/media/file/fossil-id-guide062812-accessible.pdf

 

Peng, J. & Russell, A.P. & Brinkman, D.B. (2001). “Vertebrate microsite assemblages (exclusive of mammals) from the Foremost and Oldman formations of the Judith River group (Campanian) of Southeastern Alberta : an illustrated guide.” Provincial Museum of Alberta Natural History, Occassional Paper No. 25

 

Cyclurus fragosus

 

Cyclurus was an amiid, like the living bowfin and would have closely resembled it. They possess cylindrical, blunt palatal teeth suited for crushing things, but also conical, curved teeth in the jaws for grasping (marginal teeth). Like the gar, they are a holostean fish, however scales have yet to be attributed to them in the HCF. The extant bowfin does not have ganoid scales, rather “cycloid” scales which lack enameloid and possess concentric growth lines; I have found fragments of similar scales, but they could well belong to another fish. I find Cyclurus jaws and teeth, shed palatal teeth being particularly common. One of the coolest fossils I found was a large section of palatal bone with dozens of teeth still in it, the teeth easily come loose, so I didn’t risk cleaning out all the sand. 

 

Identification: Their palatal teeth are cylindrical and blunt, the domed tips often worn flat. The marginal teeth are conical, recurved, and uncarinated, bearing no surface details. Jaw elements were identified by comparison with figures and descriptions in Gaudant (1992).

 

Bowfin jaws and teeth. A) enlarged view of a marginal tooth (no scale); B) palatal bone sections with intact teeth; C) maxillae; D) dentary with unassociated marginal teeth.

 

Gaundant 1992

 

The modern bowfin (Amia) - the only living representative of the amiids; Cyclurus would’ve looked similar.  Photo by Joel Sartore. 

 

Gaudant, Jean . 1992. "Kindleia" fragosa Jordan and "Stylomyleodon" lacus Russell: two amiid fishes from the Late Cretaceous and the Paleocene of Alberta, Canada. Canadian Journal of Earth Sciences. 29(1): 158-173. https://doi.org/10.1139/e92-015

 

 

Holostei indet.

 

I found a few holostean-grade scales that haven’t been attributed to more precise taxa, and are referred to as holostean “A” and “B” in the literature. These are not gar and are something else. 

 

Identification: Holostean A and B are distinguished by simple flat enameloid in the former, and ornamented in the latter. They are distinguishable from gar scales through a “peg” and “socket” most visible on the interior surface. The enameled edge may be serrated.

 

Holostean (non-lepisosteid) scales

 

Brinkman et al. 2014

 

Comparison of holostean ganoid scales

 

DeMar, D.G. “An Illustrated Guide to latest Cretaceous Vertebrate Microfossils of the Hell Creek Formation of northeastern Montana.” Unpublished. https://naturalhistory.si.edu/sites/default/files/media/file/fossil-id-guide062812-accessible.pdf

 

Brinkman, Donald B., Michael G. Newbrey, and Andrew G. Neuman. "Diversity and paleoecology of actinopterygian fish from vertebrate microfossil localities of the Maastrichtian Hell Creek Formation of Montana." Through the end of the Cretaceous in the type locality of the Hell Creek Formation in Montana and adjacent areas 503 (2014): 247.

 

Peng, J. & Russell, A.P. & Brinkman, D.B. (2001). “Vertebrate microsite assemblages (exclusive of mammals) from the Foremost and Oldman formations of the Judith River group (Campanian) of Southeastern Alberta : an illustrated guide.” Provincial Museum of Alberta Natural History, Occassional Paper No. 25

 

Teleostei

 

A group of bony fish that are mostly represented by small mm-scale vertebrae and partial jaws. I’ve been able to more precisely ID a couple of them thanks to Brinkman et al. 2014. These fish are very diverse today, almost every bony fish you can think of is a teleost, but they were less diverse in the Late Cretaceous. They probably would’ve been prey for the gar and bowfin, turtles, and juvenile crocodilians. 

 

Identification: In general, teleost fossils are very small, just a couple of mm in size. Their vertebrae come in many varieties, but are generally cylindrical and have prominent struts on the lateral surface. Brinkman et al. 2014 present many types and provide a much more thorough breakdown. Their jaws are small and possess many teeth in many rows which are unlikely to still be attached. My IDs for Estesesox and Priscacara follow from the figures and descriptions in Brinkman et al. 2014.

 

A) Acanthomorph type HC-2 atlas vertebra; B ) pharyngeal teeth; C) esocoid Estesesox sp. left dentary; D) perciform Priscacara sp. right dentary

 

Brinkman, Donald B., Michael G. Newbrey, and Andrew G. Neuman. "Diversity and paleoecology of actinopterygian fish from vertebrate microfossil localities of the Maastrichtian Hell Creek Formation of Montana." Through the end of the Cretaceous in the type locality of the Hell Creek Formation in Montana and adjacent areas 503 (2014): 247.

 

Estes, R., 1964. Fossil vertebrates from the Cretaceous Lance Formation, eastern Wyoming. University of California Publications in Geological Sciences 49. University of California Press, Berkeley. 

 

Acipenser “erucifer”

Least common among the bony fishes appears to be sturgeons (in this deposit anyway). These fish are still around today (in fact the genus Acipenser is extant) and inhabit freshwater and estuarine waters, though many species’ continued survival is threatened by humans. They can grow to be quite large, between 5-10 ft and weigh a few hundred pounds. They are bottom feeders, sucking up mollusks, insect larvae, and perhaps small fishes into their toothless jaws. Interestingly, despite being an actinopterygian, they possess a cartilaginous skeleton. Their skull and back are armored with unique ornamented bone, though I imagine the only predators adults had to be concerned about were crocs. The only diagnostic microsite material will be ornamented dermal bone and spines. I hadn’t recognized any sturgeon fossils until last month, so I’m quite happy to have “reeled in” this scarce fish I knew could be present.

 

Identification: A. “erucifer” dermal bone is ornamented by ridges and deep grooves, not to be confused with holostean bones which are textured with bumps. I use the specific name in parentheses, following the lead of Brinkman et al. 2014 to indicate uncertainty in nomenclature.

 

Acipenser “erucifer” ornamented dermal bone - just a piece, but larger than the holotype! We now know HCF sturgeons from remarkably complete specimens. Squares = 1 cm.

 

Acipenser erucifer holotype, a fragment of dermal bone. Scale in mm. (Hilton & Grande 2006)

 

Stellate sturgeon (Acipenser stellatus). Photo by Joel Sartore.

 

Hilton, Eric J., and Lance Grande. “Review of the Fossil Record of Sturgeons, Family Acipenseridae (Actinopterygii: Acipenseriformes), from North America.” Journal of Paleontology 80.4 (2006): 672–683. Web.

 

Brinkman, Donald B., Michael G. Newbrey, and Andrew G. Neuman. "Diversity and paleoecology of actinopterygian fish from vertebrate microfossil localities of the Maastrichtian Hell Creek Formation of Montana." Through the end of the Cretaceous in the type locality of the Hell Creek Formation in Montana and adjacent areas 503 (2014): 247.

 

Edited May 26 by ThePhysicist

[ThePhysicist]

Chondrichthyes (cartilaginous fishes)

 

Starting out as a shark tooth collector, I have a soft spot for cartilaginous fishes, and one of my initial lofty goals was to find a shark tooth.

 

Myledaphus pustulosus

 

By number, the most abundant identifiable fossils are Myledaphus teeth, I’ve literally found hundreds. It was a guitarfish with polygonal-shaped teeth tessellated into a crushing pavement. It probably fed on the abundant mollusks present. I occasionally find their denticles which are spiny “little teeth” imbedded throughout their skin; you didn’t want to pet them.

 

Identification: Their teeth are polygonal in occlusal view (usually hexagonal, or rhombic for smaller teeth), with bilobate roots. The root length / crown height ratio varies, supposedly by position in the mouth. The unworn occlusal surface is textured with bumps, but most teeth have some degree of feeding wear so they are commonly smoothed out. The bleached color has been interpreted as a sign of the tooth being digested by the fish. Their denticles come in two kinds, one is squat the other is tall and narrow, each have ridges that splay out radially from the the tip, which is shiny, coated in enameloid, and oriented distally.

 

I’ve so far collected hundreds of Myledaphus teeth with a variety of size, wear, and morphology.

 

Sample Myledaphus teeth and denticles. A) teeth; B) denticles; C) occlusal view of teeth

 

Hoffman et al. 2018

 

Reconstruction of Myledaphus, by Liam Elward. We actually have a fairly complete specimen of Myledaphus from Canada that informs its body profile.

 

Brian L. Hoffman, Jeffrey S. Jensen, Scott A. Hageman "Dental Structure of the Late Cretaceous (Maastrichtian) Guitarfish (Neoselachii: Batoidea) Myledaphus pustulosus from the Hell Creek Formation of Garfield County, Montana," Transactions of the Kansas Academy of Science, 121(3-4), 279-296, (1 September 2018)

 

Gates, Terry A., Eric Gorscak, and Peter J. Makovicky. "New Sharks and Other Chondrichthyans from the Latest Maastrichtian (Late Cretaceous) of North America." Journal of Paleontology 93.3 (2019): 512-30. 

 

Lonchidion selachos

 

Lonchidion was one of the last of the hybodonts, a lineage of shark-like fishes spanning nearly 300 million years before they went extinct along with the non-avian dinosaurs. Lonchidion had barbed spines on their dorsal fins and a durophagous dentition more suited to grinding than grasping. Like most hybodont teeth, their roots are fragile and their teeth are only rarely found complete. In this deposit they seem to be fairly rare; I’ve thus far only found three.

 

Identification: In occlusal view, their crowns are “T” or “Y” shaped (see below), with a small protuberance on the lingual face. In unworn teeth, they have a single ridge that runs mesio-distally along the apex of the cusp. 

 

A rare, rooted (although worn) Lonchidion tooth in multiple views. I was especially happy to find this one!

 

Published, rooted L. selachos tooth in multiple views, scale = 1 mm. (Wynd et al. 2020)

 

Sharks from the HCF, art by Brennon Valdez. I’d really like to complete my HCF shark collection, but alas that might take a while.

 

Wynd, B.M. & Demar, D.G. & Wilson, G.P. (2020) “Euselachian diversity through the uppermost Cretaceous Hell Creek Formation of Garfield County, Montana, USA, with implications for the Cretaceous-Paleogene mass extinction in freshwater environments.” Cretaceous Research, 113, Article 104483

DOI: 10.1016/j.cretres.2020.104483

 

Gates, Terry A., Eric Gorscak, and Peter J. Makovicky. "New Sharks and Other Chondrichthyans from the Latest Maastrichtian (Late Cretaceous) of North America." Journal of Paleontology 93.3 (2019): 512-30. 

 

Restesia americana / Galagadon nordquistae

 

A couple of species of small carpet sharks with similarly small teeth. Their teeth are uncommon and hard to find at just a mm or two in size; I have to sieve about 30 lbs of sediment to find one, and get very excited when I do! Galagadon was only recently described, and yes was named for its similarity to the ships in Galaga.

 

Identification: Both sharks are similar with a single pointed cusp. The root is bilobate and the lobes have been described as heart-shaped in basal view. The genera differ in part by ridges on the labial face of the crown.

 

A handful of Galagadon teeth, each about ~ 1 mm in size. They’re about the size they can get stuck in the voids of the foam in gem jars

 

Gates, Terry A., Eric Gorscak, and Peter J. Makovicky. "New Sharks and Other Chondrichthyans from the Latest Maastrichtian (Late Cretaceous) of North America." Journal of Paleontology 93.3 (2019): 512-30. 

 

A few sharks of the HCF; these were the most difficult to photograph with their small sizes. A) Galagadon nordquistae; B ) Restesia americana; C) Lonchidion selachos with feeding wear.

 

Terry et al. 2019

 

Reconstruction of Galagadon, by Velizar Simeonovski.

 

 

Edited May 26 by ThePhysicist

[ThePhysicist]

Lissamphibia (amphibians)

 

Amphibians really help flesh out our picture of this ecosystem, fairly conclusively supporting it being freshwater with little to no marine influence. Cullen et al. 2016 note the utility of amphibians and sharks as environmental indicators; with the prevalence of amphibians and scarcity of hybodonts or other typically marine animals, we can fairly confidently call this a freshwater ecosystem. It must have also been sufficiently humid to keep their skin hydrated. There must also have been suitably still water around to lay their eggs (for the species that lay them in water). For frogs to live here, there must have been a decent population of insects to feed on.

 

Cullen, TM., Fanti, F., Capobianco, C., Ryan, MJ., and Evans, DC. (2016). A vertebrate microsite from a marine-terrestrial transition in the Foremost Formation (Campanian) of Alberta, Canada, and the use of faunal assemblage data as a palaeoenvironmental indicator. Palaeogeography, Palaeoclimatology, Palaeoecology 444: 101-114. doi:10.1016/j.palaeo.2015.12.015

 

 

Anura (frogs)

 

There seems to be a preservation bias in the HCF that favors large animals, so small frogs with fragile skeletons will not be easy to find and identify. Like most other Late Cretaceous deposits, anurans are only known from isolated, fragmentary remains, so not much can be said other than the fact there were frogs present. It’s fun to imagine that perhaps they along with insects dominated the night soundscape. I’ve so far only found a couple of jaw fragments.

 

Identification: Jaw fragments are easily distinguished from salamanders/lizards by bumps on the labial surface, and a very short tooth shelf. Other parts are also identifiable, but I don’t know them well enough yet to have ID’d them in my collection. I’m currently studying Roček et al. 2010 which has dozens of high-quality images of Cretaceous anuran elements.

 

Frog jaw fragments

 

DeMar, D.G. “An Illustrated Guide to latest Cretaceous Vertebrate Microfossils of the Hell Creek Formation of northeastern Montana.” Unpublished. https://naturalhistory.si.edu/sites/default/files/media/file/fossil-id-guide062812-accessible.pdf

 

Peng, J. & Russell, A.P. & Brinkman, D.B. (2001). “Vertebrate microsite assemblages (exclusive of mammals) from the Foremost and Oldman formations of the Judith River group (Campanian) of Southeastern Alberta : an illustrated guide.” Provincial Museum of Alberta Natural History, Occassional Paper No. 25

Roček, Z., Eaton, J.G., Gardner, J. et al. Evolution of anuran assemblages in the Late Cretaceous of Utah, USA. Palaeobio Palaeoenv 90, 341–393 (2010). https://doi.org/10.1007/s12549-010-0040-2

 

Urodela (salamanders)

 

Like swamps and temperate forests of today, the HCF was populated with salamanders. I’ve only been able to identify vertebrae and dentary fragments. I’m wary of identifying these more precisely, but common genera include Scapherpeton and Habrosaurus.

 

Identification: jaw fragments have a largely featureless (smooth) outer surface, the teeth have the pleurodont style attachment but they are rarely intact. Vertebrae are amphicoelous (concave on both sides). They have a narrow anterior-distal ridge on the ventral side.

 

Salamander jaw fragments. A) premaxilla; B) dentary fragments (Scapherpeton?); C) jaw fragment with intact teeth (Habrosaurus?). 

 

Salamander vertebrae. A) atlantes; B) anterior/distal views of trunk vertebrae; C) dorsal view of trunk vertebra; D) caudal vertebra; E) lateral view of trunk vertebra; F) ventral view of a large trunk vertebra.

 

From DeMar’s micro guide

 

Likely a salamander jaw fragment still in the matrix

 

Reconstruction of Habrosaurus by Liam Elward.

 

DeMar, D.G. “An Illustrated Guide to latest Cretaceous Vertebrate Microfossils of the Hell Creek Formation of northeastern Montana.” Unpublished. https://naturalhistory.si.edu/sites/default/files/media/file/fossil-id-guide062812-accessible.pdf

 

Estes, R., 1964. Fossil vertebrates from the Cretaceous Lance Formation, eastern Wyoming. University of California Publications in Geological Sciences 49. University of California Press, Berkeley. 

 

Gardner, J.D. (2003), Revision of Habrosaurus Gilmore (Caudata; Sirenidae) and relationships among sirenid salamanders. Palaeontology, 46: 1089-1122. https://doi.org/10.1046/j.0031-0239.2003.00335.x

 

Peng, J. & Russell, A.P. & Brinkman, D.B. (2001). “Vertebrate microsite assemblages (exclusive of mammals) from the Foremost and Oldman formations of the Judith River group (Campanian) of Southeastern Alberta : an illustrated guide.” Provincial Museum of Alberta Natural History, Occassional Paper No. 25

 

Edited May 26 by ThePhysicist

[ThePhysicist]

Crocodyliformes (crocodiles)

 

Just like you may find in the south of the USA today, the rivers and swamps of the HCF played host to these persevering aquatic predators. The two most common genera were Brachychampsa and Borealosuchus, both of which survived the K-Pg extinction event. 

 

Crocodyliformes indet.

 

Unfortunately most microfossils of Brachychampsa and Borealosuchus are indistinguishable. The most common distinctive fossils are teeth and osteoderms which were bone plates that studded their backs. 

 

Identification: teeth are conical, erect, and carinated. They may have smooth enamel or striations. Osteoderms are marked by large, deep rounded pits on the dorsal surface with a central antero-distal ridge, the ventral surface is flat and smooth.

 

Bennett, GE. (2012) Community structure and paleoecology of crocodyliforms from the upper Hell Creek Formation (Maastrichtian), eastern Montana, based on shed teeth. Jeffersoniana. 2012;28:1–15.

 

DeMar, D.G. “An Illustrated Guide to latest Cretaceous Vertebrate Microfossils of the Hell Creek Formation of northeastern Montana.” Unpublished. https://naturalhistory.si.edu/sites/default/files/media/file/fossil-id-guide062812-accessible.pdf

 

Brachychampsa montana

This is an early “alligator”, and is commonly reported from the HCF. They notably possessed blunt, bulbous teeth in the back of the mouth that many suppose would’ve been especially good for predating on turtles.

 

Identification: Their only distinctive microfossils are posterior teeth, which are bulbous and blunt with basal constriction, sometimes likened to “acorns.” Many show signs of feeding wear.

 

DeMar, D.G. “An Illustrated Guide to latest Cretaceous Vertebrate Microfossils of the Hell Creek Formation of northeastern Montana.” Unpublished. https://naturalhistory.si.edu/sites/default/files/media/file/fossil-id-guide062812-accessible.pdf

 

Crocodyliform fossils. A) partial osteoderm; B) crocodyliform teeth; C) enlarged view of small Brachychampsa posterior teeth.

 

More crocodyliform osteoderms

 

Reconstruction of Brachychampsa by Liam Elward.

 

Nota bene: Recently, many teeth previously considered to be avian are now recognized to likely belong to juvenile crocodyliforms. Below are two examples I found whose morphologies have previously been reported as avian.

 

 

Identified morphologies previously referred to Avialae. Morphology M10 were determined by the authors to most likely to indeed be avian. (Acorn & Currie 2023)

 

Mohr SR, Acorn JH, Currie PJ (2023) Putative avian teeth from the Late Cretaceous of Alberta, Canada, are more likely from crocodilians. PLOS ONE 18(3): e0283581. https://doi.org/10.1371/journal.pone.0283581

 

 

Champsosaurus sp.

 

This aquatic reptile looks a lot like a crocodile, but it’s simply a result of convergence. It’s extinct today, but it did outlive the non-avian dinosaurs and survived the K-Pg extinction event. Champsosaurus had a long snout with narrow teeth good for grasping slippery fish, much like modern gharials.

 

Identification: their teeth are fairly common, they are mostly tall and narrow cones with opposed carinae that proceed half if not most the length of the crown. At the base are striations that quickly diminish towards the tip, “apically.” Teeth further back in the mouth are more stout. I’ve seen many Melvius (bowfin) teeth misidentified as “Champsosaurus” and many Champsosaurus misidentified as lepisosteid.

 

Typical Champsosaurus teeth, highlighting distinguishing features. 

 

A Champsosaurus tooth still in the matrix.

 

A Champsosaurus nabs a gar fish, art by Beth Zaiken.

 

DeMar, D.G. “An Illustrated Guide to latest Cretaceous Vertebrate Microfossils of the Hell Creek Formation of northeastern Montana.” Unpublished. https://naturalhistory.si.edu/sites/default/files/media/file/fossil-id-guide062812-accessible.pdf

 

Peng, J. & Russell, A.P. & Brinkman, D.B. (2001). “Vertebrate microsite assemblages (exclusive of mammals) from the Foremost and Oldman formations of the Judith River group (Campanian) of Southeastern Alberta : an illustrated guide.” Provincial Museum of Alberta Natural History, Occassional Paper No. 25

 

Testundines (turtles)

 

Turtles make an appearance in this deposit, mostly as distinctive shell fragments with pitted surfaces. The patterning of the pitting in the shell is useful for identification.

 

Trionychidae (softshsell turtles)

 

The most common turtles were softshells. The family is still around today, so we have a good understanding of what they looked like and how they behaved. They have a leathery smooth outer shell that allows them to move very quickly in the water and bury themselves in seconds. They like to hide in the sand and ambush passing fish. These guys also had to watch out for the shell-crunching teeth of Brachychampsa!

 

Identification: The carapace’s external surface is pocked by circular pits that near the shell’s margins merge to form channels. Carapace fragments are flat on both sides and have roughly uniform thickness. 

Basilemys sp.

 

An extinct, large land-dwelling turtle that would’ve functioned similar to modern tortoises, feeding on low plants and mosying around. I found it to be less common than softshell turtles, which makes sense, since they didn’t necessarily spend a lot of time near the river.

 

Identification: The carapace surface texture is formed from low semi-triangular pits, the ridges take on a chain link appearance. The carapace is typically thicker than that of trionychids.

 

Sample softshell turtle carapace fragments.

 

More turtle carapace fragments. A) Basilemys sp.; the rest are trionychid

 

Trionychid turtles in their natural habitat, art by Sergey Krasovskiy.

 

DeMar, D.G. “An Illustrated Guide to latest Cretaceous Vertebrate Microfossils of the Hell Creek Formation of northeastern Montana.” Unpublished. https://naturalhistory.si.edu/sites/default/files/media/file/fossil-id-guide062812-accessible.pdf

 

Jordan C. Mallon & Donald B. Brinkman (2018) “Basilemys morrinensis, a new species of nanhsiungchelyid turtle from the Horseshoe Canyon Formation (Upper Cretaceous) of Alberta, Canada,” Journal of Vertebrate Paleontology, 38:2, DOI: 10.1080/02724634.2018.1431922

 

 

Squamata (Lizards)

 

Squamates also include snakes, but I’ve yet to find a definitive snake fossil. I have however found several lizards, mostly jaw fragments, but a couple of vertebrae as well. 

 

Polyglyphanodontia

 

These are an extinct clade of lizards that were dominant in North America during the Late Cretaceous. They may have resembled the modern tegu lizards and probably fed on a number of small animals and plants. There are several lizards described from the HCF, and to my unlearned eyes, all look very similar so I’m hesitant to even hazard a more precise ID on any of these. Leptochamops is apparently a common genus, and the larger dentary I found looks similar.

 

Identification: jaws are similar to those of salamanders, but are generally more slender, possess multiple foramina on the labial surface, and their teeth are more commonly intact, with pointed tips, ornamentation, and sometimes multiple cusps. Gao 1996 is a great reference.

 

Lizard jaw fragments. 

 

Gao 1996

 

Reconstruction of Chamops, a polyglyphanodontian lizard. Art by Liam Elward.

 

Gao, K., and Fox, R. C., 1996, Taxonomy and evolution of Late Cretaceous lizards (Reptilia: Squamata) from Western Canada: Bulletin of Carnegie Museum of Natural History, no. 33, p. 1-107. 

 

Longrich, N. R., Bhullar, B. A. S. & Gauthier, J. A. (2012). Mass extinction of lizards and snakes at the Cretaceous–Paleogene boundary. Proceedings of the National Academy of Sciences, USA 109, 21396–21401.

 

Varanoidea

 

These large lizards are kin to modern monitors like the Komodo dragon. They possess sharp, finely serrated teeth and long claws good for climbing and digging. They likely preyed on smaller animals like other lizards and mammals, and may have been the bane of parent dinosaurs as some paleontologists have suggested they could raid dinosaur nests.

 

Identification: teeth are blade-like with extremely fine serrations on both carinae. In basal view, the profile is oval with the mesial carina projecting like a wing - they are not compressed as in theropods, and the serrations are much finer than even Richardoestesia (see below). The vertebrae are opisthocoelous and have a distinct antero-distal groove on the ventral surface.

 

Varanoid “monitor lizard” fossils. A) trunk vertebra, missing a good portion of the process; B) tooth showing basal cross section silhouette and closeup of serrations.

 

Gao 1996

 

A large varanoid resists the approach of a young tyrannosaurid. Art by Julio Lacerda.

 

Estes, R., 1964. Fossil vertebrates from the Cretaceous Lance Formation, eastern Wyoming. University of California Publications in Geological Sciences 49. University of California Press, Berkeley. 

 

Gao, K., and Fox, R. C., 1996, Taxonomy and evolution of Late Cretaceous lizards (Reptilia: Squamata) from Western Canada: Bulletin of Carnegie Museum of Natural History, no. 33, p. 1-107. 

Edited May 26 by ThePhysicist

[ThePhysicist]

Mammalia (mammals)

 

Our closest cousins in this time were small animals that didn’t get much larger than a house cat. They were still very diverse but didn’t occupy the upper echelons of the food web that they do today. It would take an imminent catastrophe for them to occupy a fuller range of niches. Most mammal fossil I’ve identified are teeth and jaw fragments. Mammals have notoriously complex teeth and are quite the challenge to identify precisely, even with the aid of Bill Clemens’ books.

 

Metatheria (“Marsupials”)

 

The most common mammals I found were marsupials, they would have resembled something like an opossum. Their teeth look so similar that I again don’t yet dare ID them more precisely (a challenge for a separate thread perhaps). Remarkably I found jaw fragments, one even has teeth! Many of the isolated teeth also retained their delicate roots; it still amazes me that they survived the river and millions of years of geology. Unlike most animals here, mammals only produce two sets of teeth throughout their lives, so it’s more common for them to be found rooted or partially rooted. Common metatherians in HCF include Alphadon and Didelphodon.

 

Identification: Mammal teeth are quite complex and vary quite a lot throughout a single dentition, but are also superficially very similar to related species. Mesozoic mammal identification really requires an entire separate topic. To oversimplify, metatherian/eutherian teeth have many tall sharp cusps, compared to multituberculates. 

 

Quoting the simplified description from Dave DeMar’s micro guide:

“The upper molars of metatherians and eutherians are triangular shaped with three major cusps or bumps on the occlusal surface of the crown. The main differences between metatherian and eutherian upper molars are that metatherians have more small cusps on the outer side (labial) of the occlusal surface of the tooth and have a front to back (mesiodistal) longer tooth (Fig. 37 uppers). The lower molars are more complex and can be divided into two major parts: a triangular-shaped trigonid and a circular or oval talonid. In metatherians the talonid is more round and the cusps are less evenly spaced on the top of the crown (Fig. 37 lowers).”

 

From DeMar’s micro guide.

 

Sample metatherian teeth. A) lower molars; B) lower molar in occlusal view showing cusp pattern; C) upper molars; D) premolars

 

Restoration of Alphadon, a small insectivorous metatherian. Art by Misaki Ouchida

 

Lillegraven, Jason A.. “Latest Cretaceous mammals of upper part of Edmonton Formation of Alberta, Canada, and review of marsupial-placental dichotomy in mammalian evolution.” (1969).

 

Clemens, William A. Fossil Mammals of the Type Lance Formation Wyoming: Marsupalia. Part II. University of California Press, 1963.

 

Multituberculata

 

Multituberculates are an extinct, but very successful group of small mammals that existed for 130 million years before disappearing in the Eocene. Ecologically they likely were similar to rodents and may have competed with them. They are so-named for their multi-cusped molars that can resemble legos (thanks to Steve Brusatte for the analogy). Another distinctive tooth form are the lower 4th premolars (p4), they take on a “buzzsaw” shape, illustrated below. I’ve only found a few broken examples, and hope I can find more complete ones in the future, particularly p4’s.

 

Identification: molars have two or three rows of many tubercles, whose size, shape and quantity vary by position and species. Upper premolars are small with three to four cusps and long roots. The fourth lower premolar is blade like with a jagged cutting edge, resembling a buzzsaw, with ridges that proceed across the face of the crown on both sides. Incisors are elongate and have a flattened mesial face, there is of course variation among species with additional features like accessory cusps.

 

Sample multituberculate teeth. A) large multituberculate upper incisor, likely Meniscoessus robustus; B) multituberculate molar; C) Cimolodon sp. right m2 in occlusal and lateral views; D) multituberculate P1-3’s.; E) Mesodma sp. right p4, drawing copied from Clemens (1964).

 

Mammal jaw fragments. A) multituberculate with p4 intact; B) metatherian left dentary; C) metatherian right dentary with intact teeth.

 

Mesodma parent with their young, by Andrey Atuchin.

 

Clemens, William A. Fossil Mammals of the Type Lance Formation Wyoming: Introduction and Multituberculata. Part I. University of California Press, 1963.

 

Lillegraven, Jason A.. “Latest Cretaceous mammals of upper part of Edmonton Formation of Alberta, Canada, and review of marsupial-placental dichotomy in mammalian evolution.” (1969).

 

Eutheria (Placental Mammals)

 

Back in the Maastrichtian, us eutherian mammals were not as plentiful as we are today. At the time, there was no indicator that this minority group of mammals would come to dominate the planet. I was simply astonished that I found one.

 

Gypsonictops sp.

 

A eutherian-grade mammal with a poorly understood phylogeny. Of the mammals presented in this collection, this one is most closely related to us.

 

Identification: this is an odd tooth, with only two cusps on the trigonid (anterior portion of the tooth) - recall the norm is three. It took several weeks for me to figure the ID out, but it’s a dead ringer for the 4th lower premolar of Gypsonictops. I quietly hoped it was a novel species to donate, but alas, the professionals beat me to the discovery by 50+ years.

 

4th lower premolar (p4) of the eutherian, Gypsonictops

 

Gypsonictops dentary in multiple views, p4 circled in red. (Lillegraven 1969)

 

Lillegraven, Jason A.. “Latest Cretaceous mammals of upper part of Edmonton Formation of Alberta, Canada, and review of marsupial-placental dichotomy in mammalian evolution.” (1969).

Edited May 26 by ThePhysicist

[ThePhysicist]

Dinosaurs

 

At last, the terrible lizards. As marvelous as all the other animals are, it’s hard to resist my affinity for dinosaurs. These in particular are significant for being among the last of the non-avian dinosaurs to exist. In a larger evolutionary context, many of the HCF dinosaurs were exceptional for being the largest (or nearly) of their respective clades. It must have been a truly rich environment to support these numerous, impressive animals. I have specimens from most of the major players in the ecosystem, and for some taxa I have specimens that span their ontogeny. In microsites, they are mostly represented by teeth, which is fine by me since teeth are usually distinctive and very informative.

 

Ornithischia

 

Thescelosaurus sp.

 

Thescelosaurus was a small bipedal herbivore (though some suggest it’s omnivorous) that possibly burrowed. It is well-represented in the deposit by several teeth, though most are heavily worn. It was probably a very common dinosaur in the HCF ecosystem. 

 

Identification: Thescelosaurus had a heterodont dentition (retaining the basal condition in ornithischians) so there are a couple of tooth forms which can be separated into medial “cheek” teeth and premaxillary “front” teeth. The medial teeth are philodont/fan-shaped with many apicobasal ridges that extend across the whole crown. Unlike the similar teeth of pachycephalosaurids, there is no prominent cingulum or median ridge. The premaxillary teeth are conical and bulbous at the base. Unlike the premaxillary teeth of pachycephalosaurids, there is no fluting or distal serrations.

 

Thescelosaurus teeth, from both anterior and medial “cheek” positions. Many are heavily tumbled and worn, leaving them with minimal to no enamel.

 

Skull of Thescelosaurus neglectus, highlighting its heterodont dentition. (Hudgins et al. 2022)

 

A family of burrowing Thescelosaurus. Art by Anthony Hutchings.

 

Hudgins, Michael Naylor, Philip J. Currie, and Corwin Sullivan. "Dental assessment of Stegoceras validum (Ornithischia: Pachycephalosauridae) and Thescelosaurus neglectus (Ornithischia: Thescelosauridae): paleoecological inferences." Cretaceous Research 130 (2022): 105058.

 

Leptoceratops sp.

 

This was a small cousin of the more famous Triceratops. They closely resemble more “primitive” (basal), earlier members of Ceratopsia. They lacked horns, but still had a large beak and small frill. Some researchers have suggested they too were burrowing animals. I’ve so far mostly found tooth chunks, but also a couple of small rooted teeth from young animals (since they’re rooted, it unfortunately means those individuals didn’t survive to adulthood).

 

Identification: leptoceratopsid teeth are similar to those of their cousins the ceratopsids, the most obvious difference is the root, which is single and smoothly textured in leptoceratopsids, and double in ceratopsids. Leptoceratopsids have a pronounced cingulum, which forms a shelf at the base of the crown.

 

A small, rooted Leptoceratops tooth

 

Another small, rooted Leptoceratops tooth. I’d like to find rooted teeth of more species, but guess I can’t complain.

 

Ryan et al. 2012

 

Ryan, Michael & Evans, David & Currie, Philip & Brown, Caleb & Brinkman, Donald. (2012). New leptoceratopsids from the Upper Cretaceous of Alberta, Canada. Cretaceous Research. 35. 69-80. 10.1016/j.cretres.2011.11.018. 

 

Ceratopsidae / Triceratops sp.

 

Triceratops was one of the last and largest of the ceratopsids. Ceratopsids coevolved with their primary predators the tyrannosaurids in an escalating arms race, each arguably reaching their zenith with Triceratops and Tyrannosaurus, respectively. Triceratops had hundreds of teeth in their mouth at a time, and like sharks, regularly and continually shed and replaced them as they were ground down. Ceratopsid shed “spit” teeth are fairly common, usually with some evidence of river-tumbling and loss of enamel. Given how overwhelmingly abundant Triceratops is within the HCF (compared to Torosaurus), these are most likely to be from Triceratops.

 

Identification: Unworn teeth are leaf-like in shape with an apicobasal ridge which is offset towards the mesial edge. The enamel is rugose, especially on the margins (see B below). Shed teeth are more commonly found, which can be more difficult to identify since they often are worn and weathered into a number of different forms.  

 

Typical ceratopsid shed teeth, showing a variation in shapes from wear - note the flattened top surfaces

 

Ceratopsid teeth, unfortunately none are complete. A) shed teeth “spitters”; B) fragments showing preserved rugose enamel; C) occlusal surfaces on shed teeth showing feeding wear (scale = 15 mm).

 

Unworn ceratopsid teeth (Mallon & Anderson 2014)

 

A group of Triceratops fends off a gang of small tyrannosaurs. Art by Anthony Hutchings.

 

Mallon JC, Anderson JS (2014) The Functional and Palaeoecological Implications of Tooth Morphology and Wear for the Megaherbivorous Dinosaurs from the Dinosaur Park Formation (Upper Campanian) of Alberta, Canada. PLoS ONE 9(6): e98605. doi:10.1371/journal.pone.0098605

 

Gregory M. Erickson et al. ,Wear biomechanics in the slicing dentition of the giant horned dinosaur Triceratops. Sci. Adv.1,e1500055(2015).DOI:10.1126/sciadv.1500055

 

Edmontosaurus annectens

 

Hadrosaurs “duckbills” were one of the most successful and interesting dinosaurs in the Cretaceous. Edmontosaurus was a large hadrosaur, comparable to Triceratops in its abundance. They could grow to the size of T. rex and could’ve lived in large herds hundreds strong, as indicated by massive bone beds. They were absolute eating machines with highly sophisticated teeth rivaling the tissue complexity of mammals, and mobile skulls allowing for a range of chewing motions. Some of the most common dinosaur fossils in the HCF are their teeth; they possessed hundreds of teeth in their mouths at a time, constantly grinding them down root and all.

Identification: Their teeth are generally lanceolate or diamond-like in shape, with a central apicobasal ridge. They are usually very symmetric about the long axis of the tooth. There is no cingulum and they have smoother enamel than ceratopsids. Shed teeth have a “squashed square” shape in occlusal view (see A below) and may have a 4-way branching pattern on the occlusal surface.

 

Edmontosaurus teeth, straddling its ontogeny. A) young juvenile teeth; B) maxillary tooth; C) large adult dentary tooth

 

Edmontosaurus shed/“spitter” teeth, most show significant river tumbling and feeding wear. A) occlusal view showing cross section and wear surface details

 

An Edmontosaurus wanders to the river for a drink. Art by Alain Bénéteau. 

 

A note on “shed teeth” (prompted by a question from @Mikrogeophagus): 

 

It's said in LeBlanc et al. 2016, "...unlike most vertebrates, hadrosaurids did not shed their teeth..." The teeth aren't shed as in the fashion of sharks etc., but are continuously ground down root and all. They seem to have been connected and advanced by ligaments. Of the millions "nub" teeth found, I think they were indeed lost/shed. My guess would be that there's not much left at that point holding them in, so occasionally they fell out. This would perhaps explain why they are vastly more common than more complete teeth. After all, they make up a small fraction of the number of teeth in the mouth at a given time, and you can certainly only find complete/semi-complete teeth from a dead animal.

 

Mallon & Anderson 2014

 

Gregory M. Erickson et al., Complex Dental Structure and Wear Biomechanics in Hadrosaurid Dinosaurs. Science 338, 98-101 (2012). DOI:10.1126/science.1224495

 

Mallon JC, Anderson JS (2014) The Functional and Palaeoecological Implications of Tooth Morphology and Wear for the Megaherbivorous Dinosaurs from the Dinosaur Park Formation (Upper Campanian) of Alberta, Canada. PLoS ONE 9(6): e98605. doi:10.1371/journal.pone.0098605

 

LeBlanc, A.R.H., Reisz, R.R., Evans, D.C. et al. Ontogeny reveals function and evolution of the hadrosaurid dinosaur dental battery. BMC Evol Biol 16, 152 (2016). https://doi.org/10.1186/s12862-016-0721-1

 

 

Ornithischia indet.

 

Commonly found are ossified tendons. These are tendons infiltrated by osteocytes and were essentially turned to bone. Both Triceratops and Edmontosaurus had a weave of tendons along their back that stiffened and supported their tails. Online you commonly see these uniquely referred to hadrosaurids (Edmontosaurus), but I don’t see what precludes them from being from ceratopsids.

 

Identification: Tendons are long and cylindrical with circular or sub-circular cross sections. They are not hollow, don’t have spongey trabecular bone, and the outer surface is often marked by grooves that are directed along the length of the tendon.

 

Sections of ossified tendons. Especially in an energetic channel environment, these fragile structures are broken into pieces. 

 

Nodosauridae cf. Denversaurus sp.

 

Nodosaurids are close cousins of the better known club-tailed ankylosaurids (they are both included in the clade Ankylosauria). They were large armored dinosaurs that would have been off the menu for most carnivores. They were low browsers eating things like ferns with comparably small leaf-shaped “philodont” teeth. Their remains aren’t very commonly preserved - some paleontologists have proffered that this apparent paucity is due to their preferred habitat being in the highlands, away from the plentiful sedimentation in the floodplains that most favorably preserved fossils. I’ve so far only found one tooth, making it one of the rarer fossils I’ve yet found in the deposit.

 

Identification: their teeth are leaf-shaped with splaying denticles on the mesial/distal edges. The labial face is recessed with a prominent cingulum, giving it a “baseball mitt” shape. The root is cylindrical and hollowed out. Compared to ankylosaurids, nodosaurid teeth are less conical and more labio-lingually flattened like a fan.

 

A worn nodosaurid tooth. All of the enamel is worn away unfortunately; this tooth may have experienced extended river transport.

 

A Tyrannosaurus encounters a nodosaurid. Art by Andrey Atuchin.

 

Mallon JC, Anderson JS (2014) The Functional and Palaeoecological Implications of Tooth Morphology and Wear for the Megaherbivorous Dinosaurs from the Dinosaur Park Formation (Upper Campanian) of Alberta, Canada. PLoS ONE 9(6): e98605. doi:10.1371/journal.pone.0098605

 

Ankylosauria indet.

 

Ankylosaurs were protected by bones in their skin, “osteoderms”, that formed a chainmail-like defense against blunt trauma from intraspecific altercations, and against penetrating bites from e.g. tyrannosaurs . One may not expect to find much more than teeth from these guys in microsites. However, these osteoderms ranged widely in size, from the size of dinner plates to small cm-scale “ossicles” which filled in the spaces between the larger plates. I believe I potentially found an ankylosaur ossicle.

 

Identification: the smallest osteoderms, “ossicles”, are cm-scale in size. Morphologically, they vary from round to oval (or irregular) in shape, and are solid bone. The candidate I found is oval in shape (not broken), solid, and has a rugose texture on one side, and  is smooth, slightly concave on the other surface.  

 

Possible ankylosaurian interstitial ossicle

 

Isolated ankylosaurian ossicles of the Oldman Fm., MT (largest ~ 1 cm in size); photo from Denver Fowler

 

Kirkland JI, Alcalá L, Loewen MA, Espílez E, Mampel L, et al. (2013) The Basal Nodosaurid Ankylosaur Europelta carbonensis n. gen., n. sp. from the Lower Cretaceous (Lower Albian) Escucha Formation of Northeastern Spain. PLOS ONE 8(12): e80405. https://doi.org/10.1371/journal.pone.0080405

 

Peng, J. & Russell, A.P. & Brinkman, D.B. (2001). “Vertebrate microsite assemblages (exclusive of mammals) from the Foremost and Oldman formations of the Judith River group (Campanian) of Southeastern Alberta : an illustrated guide.” Provincial Museum of Alberta Natural History, Occassional Paper No. 25

 

Pachycephalosauridae

 

The well-known dome-headed dinosaurs were also present in the HCF. They were relatively small ornithischians with a potentially omnivorous diet. Their fossils seem to be uncommon in the deposit, as I’ve only found a couple of candidate teeth, all significantly river-worn.

 

Identification: They had a dentition infamously similar to that of Thescelosaurus, down to bulbous, fang-like anterior premaxillary teeth. For the medial positions, the crown shape is more triangular (“spade-shaped”), with a strong median ridge flanked by denticles/ridges down the sides of each mesial/distal edge. They also have a bulbous rim at the base of the crown - a cingulum - which separates it from the root. Premaxillary teeth are more easily distinguished from those of Thescelosaurus by the presence of serrations on the distal edge.

 

A worn pachycephalosaurid medial (cheek) tooth. Illustration adapted from Fanti & Miyashita (2009).

 

Pachycephalosaurus, as depicted in Apple TV’s “Prehistoric Planet”

 

Fanti, Federico and Miyashita, Tetsuto. “A high latitude vertebrate fossil assemblage from the Late Cretaceous of west-central Alberta, Canada: evidence for dinosaur nesting and vertebrate latitudinal gradient.” Palaeogeography, Palaeoclimatology, Palaeoecology 275 (2009): 37-53.

Edited May 26 by ThePhysicist

[ThePhysicist]

Saurischia (Theropoda)

 

I begin the theropods with several “tooth taxa” that are known largely or entirely from teeth. Not much otherwise known about them, and their names and attributions can easily change as (hopefully) more substantial remains are discovered and described. Case in point is Zapsalis, which I’ll cover since I occasionally see it referred to by collectors or in slightly older publications.

 

Richardoestesia isosceles / R. gilmorei

 

Richardoestesia is a genus of enigmatic theropod known largely from its teeth. Unfortunately, that means very little is known about the animal, and all I can talk about is the tooth morphology. 

 

Intriguingly, former forum member @Troodon had a jaw that has both R. isosceles and Paronychodon morphotypes, suggesting they come from the same animal with a strongly heterodont dentition. The classification remains uncertain, but in any case, these two morphs will be synonymized in the future. Likely more material is needed before any conclusions can be drawn with confidence. 

 

Identification: Both species of Richardoestesia match the classical theropod tooth form in being “ziphodont” (labio-lingually compressed and serrated), and are characterized by very fine serrations on both carinae (~8-10 / mm). R. isosceles as its specific name suggests generally take the shape of an isosceles triangle and are much taller than they are wide. R. gilmorei teeth are usually very small, and the anterior serrations are smaller than the distal ones or not present. I tentatively refer tooth ‘E’ below to R. gilmorei, but you’ll notice the mesial denticles are comparable in size to the distal ones, so it may belong to a different taxon. 

 

Notable features of R. isosceles teeth

 

Longrich, Nick. "Small theropod teeth from the Lance Formation of Wyoming, USA." Vertebrate microfossil assemblages: Their role in paleoecology and paleobiogeography (2008): 135-158.

 

Larson DW, Currie PJ (2013) Multivariate Analyses of Small Theropod Dinosaur Teeth and Implications for Paleoecological Turnover through Time. PLoS ONE 8(1): e54329. doi:10.1371/journal.pone.0054329 

 

Paronychodon sp.

 

Another enigmatic and potential dubious genus of theropod only known from teeth. 

 

Identification: their teeth are compressed and possess several prominent longitudinal ridges on both lingual and labial faces. They are superficially similar to Zapsalis, but do not have serrations.

 

Longrich, Nick. "Small theropod teeth from the Lance Formation of Wyoming, USA." Vertebrate microfossil assemblages: Their role in paleoecology and paleobiogeography (2008): 135-158.

 

Zapsalis abradens (=Dromaeosauridae)

 

This tooth taxon is very similar to Paronychodon, and in light of recent discoveries is now known to represent premaxillary teeth of dromaeosaurids. Researchers have hypothesized that these specialized teeth may have been useful for preening feathers.

 

Identification: similar to Paronychodon, they have longitudinal ridges, but they also have serrations, larger on the distal edge (they may be absent on the mesial edge). The lingual face is flattened, the labial face is convex, giving it a ‘D’-shaped cross section. 

 

Currie, Philip J, and David C Evans. “Cranial Anatomy of New Specimens of Saurornitholestes langstoni (Dinosauria, Theropoda, Dromaeosauridae) from the Dinosaur Park Formation (Campanian) of Alberta.” Anatomical record (Hoboken, N.J. : 2007) vol. 303,4 (2020): 691-715. doi:10.1002/ar.24241

 

Ornithomimidae?

 

A family of “ostrich dinosaurs.” They had long legs and arms equipped with straight claws. Unlike many theropods that come to mind, they were toothless and may have been primarily herbivorous. 

 

Identification: There are very few identifiable remains small enough to be found in my channel matrix. I do believe however that I’ve found part of a small vertebra. It is very laterally compressed, and  lacks ventral or lateral processes. 

 

Sues, Hans-Dieter and Averianov, Alexander. 2016. "Ornithomimidae (Dinosauria: Theropoda) from the Bissekty Formation (Upper Cretaceous: Turonian) of Uzbekistan." Cretaceous Research, 57 90–110. https://doi.org/10.1016/j.cretres.2015.07.012.

 

Miscellaneous theropods, including enigmatic tooth morphologies (B-E). A) ornithomimid? vertebra (scale = 5 mm); B ) Paronychodon sp. tooth (scale = 10 mm); C) Richardoestesia isosceles teeth (scale = 10 mm); D) Zapsalis abradens (=Dromaeosauridae) tooth  (scale = 10 mm);  E) ?Richardoestesia gilmorei tooth (scale = 2.5 mm).

 

Acheroraptor temertyorum / Dromaeosauridae 

 

Dromaeosaurids / “raptors” are small, feathered dinosaurs that likely preyed on lizards, mammals, and other smaller dinosaurs. Two dromaeosaurids are currently described from the HCF, Acheroraptor and Dakotaraptor. Like other small theropods, their most common remains are teeth lost during feeding, “shed” teeth. Most teeth show signs of feeding wear at their apices.

 

Identification: All of the teeth show the classical dromaeosaurid characters of being ziphodont (compressed, serrated), recurved distally, and possessing a larger mesial serration density than distal. Acheroraptor is known for ridges that run up the length of the tooth on both sides; without that ornamentation, any other dromaeosaurid teeth are strictly indeterminate. I don’t bother with Dakotaraptor since the only teeth described in literature are the two holotype teeth and they are apparently consistent with juvenile tyrannosaurids, but I digress. 

 

Dromaeosaurid teeth showing range of morphology (which may or may not represent distinct taxa). A) indeterminate dromaeosaurid with a spalled tip; B ) indeterminate domaeosaurid with a mesial carina that twists onto the lingual side, dromaeosaurine?; C) Acheroraptor temertyorum; D) dromaeosaurid premaxillary tooth (likely A. temertyrorum); E) indeterminate dromaeosaurid, anterior tooth?

 

Note on mesial position:

 

D) above is a curious tooth, a narrow crown with an unserrated mesial carina displaced lingually. It matches “morphotype B” in Averianov et al. 2019, which the authors conclude represent mesial positions of a juvenile dromeosaurid. This also matches the conclusion of Phil Currie, given to a similar tooth in the collection of @JoeS. 

 

Juvenile dromaeosaurid anterior

 

Acheroraptor; “dromie” teeth usually aren’t all that large.

 

Feeding damage, note the rounded edges of the broken surface - indicating it continued to be used for a while before it was shed. 

 

Evans, D.C., Larson, D.W. & Currie, P.J. A new dromaeosaurid (Dinosauria: Theropoda) with Asian affinities from the latest Cretaceous of North America. Naturwissenschaften 100, 1041–1049 (2013). https://doi.org/10.1007/s00114-013-1107-5

 

Longrich, Nick. "Small theropod teeth from the Lance Formation of Wyoming, USA." Vertebrate microfossil assemblages: Their role in paleoecology and paleobiogeography (2008): 135-158.

 

Averianov, Alexander O. et al. “Theropod teeth from the Lower Cretaceous Ilek Formation of Western Siberia, Russia.” Proceedings of the Zoological Institute RAS (2019): n. pag.

 

Pectinodon bakkeri

 

Pectinodon were small theropods that were closely related to dromaeosaurs and to birds. Pectinodon is currently only known from its teeth, but its larger family, troodontids, are known much more completely. Despite their wicked-looking teeth with large serrations, there are multiple lines of evidence from morphology and stable isotope analysis of their enamel that troodontids were omnivorous. They would’ve preferred small prey like mammals and lizards, as finite element analysis suggests their teeth weren’t built as robustly as dromaeosaurs and tyrannosaurs. This is probably my holy grail of microfossils and quickly became my favorite to find. Troodontids are generally very rare fossils wherever you’re searching, so I consider myself very lucky to have found a few very nice ones.

 

Identification: These are hard to find, but easy to identify. They are ziphodont and have a strongly denticulated distal carina with triangular denticles oriented apically (towards the tip). The largest tooth here is an anterior dentary position and probably approaches the maximum size for the species (comparing it to data in the literature and TFF member collections).

 

Exquisite troodontid teeth in lingual/labial views. Note the small size and wicked distal serrations. The big one is one of my favorite fossils in my collection.

 

Identifying features of Pectinodon. The illustration is the holotype, adapted from Carpenter 1982 (to scale). These are suspected to be anterior dentary teeth; medial and posterior teeth differ in part by lack of lingual pitting, and may have fine serrations on the basal portion of the mesial carina.

 

spot it?

 

Pectinodon, as depicted in Apple TV’s “Prehistoric Planet.”

 

Carpenter, K. (1982). "Baby dinosaurs from the Late Cretaceous Lance and Hell Creek formations and a description of a new species of theropod". Contributions to Geology, University of Wyoming. 20 (2): 123–134.

 

Larson DW, Currie PJ (2013) Multivariate Analyses of Small Theropod Dinosaur Teeth and Implications for Paleoecological Turnover through Time. PLoS ONE 8(1): e54329. doi:10.1371/journal.pone.0054329 

 

Thomas M. Cullen, Brian L. Cousens; New biogeochemical insights into Mesozoic terrestrial paleoecology and evidence for omnivory in troodontid dinosaurs. GSA Bulletin 2023; doi: https://doi.org/10.1130/B37077.1

 

Tyrannosaurus rex

 

The largest theropod present in the HCF was T. rex. It was a formidable predator that grew up to about 40 ft (12 m) in length, and weighed several tons. It was built for hunting the large herbivores of the HCF like Edmontosaurus and Triceratops, equipped with a powerful bite force and large teeth. I know I won’t find a giant complete tooth, but I occasionally find decent fragments, enough to say it was around. All the pieces here show some degree of river wear on the broken surfaces, indicating they broke apart before their final deposition. 

 

Identification: It’s big. Generally any theropod tooth from the HCF over ~2 cm is tyrannosaurid. They have large, similarly-sized, rectangular/chisel-shaped serrations on both carinae. I found part of a young juvenile premaxillary tooth which has both carinae on the lingual face and a sinusoid profile to them, and a median ridge on the lingual face - it is diagnostically tyrannosauroid.

 

Typical fragments of T. rex teeth. A) my largest fragment thus far, with a portion of the anterior carina and root; B) tip of a large tooth with feeding wear - the bottom exhibits a spiral fracture, perhaps it broke off with a twisting motion; C) premaxillary tooth of a young juvenile tyrannosaurid.

 

A posteriorly-positioned tooth from a juvenile animal. Overall a decent tooth with some evidence of river wear - smoothing at the base (which is softer than the enameled crown), and enamel pitting from corrosion.

 

A larger, serrated tooth fragment. Note the slanted “blood grooves” (interdenticular sulci) at the base of the serrations, and the transverse undulations (these features aren't diagnostic, but may appear on tyrannosaurid teeth).

 

Not sure why, but I could look at serrations all day - little marvels of natural selection. And to imagine 66 million years ago these were cutting through dinosaur muscle fibers!

 

This tooth saw some action - a wear facet (caused by repeated opposing tooth-tooth contact), gouges in the enamel, and completely worn serrations (after the hard enamel wore away, continued use and softer dentine led to depressions where protruding denticles once were).

 

This fun family photo emphasizes how ridiculously outsized T. rex was - the tip of a tooth is larger than entire teeth of contemporaneous theropods! T. rex was a highly unusual animal, especially in the context of its own ecosystem.

Edited May 26 by ThePhysicist

[ThePhysicist]

Miscellaneous and Unknown

 

Unguals (claws)

 

Most amniotes that possess claws construct them in the same way - a bony core sheathed in hard keratin, e.g. as in cats and dogs. Many critters in the HCF had claws that are possible to find (although uncommon) including crocodiles, turtles, mammals, and dinosaurs of course. I’ve been lucky to find a few, but claws are poorly referenced in the literature I found, particularly on the small vertebrates they’re likely from.

 

Identification: although a broad category, many claws share common features. When complete, they will have a concave articular surface on one end where it connected to the digit, a “blood”/lateral groove, and a pointy end. This description doesn’t work for many ornithischian unguals, but to keep things short and relevant to what I’ve found, I won’t say more. Precise identification is going to be difficult for small, incomplete claws.

 

Sample unguals. A) tip of a theropod dinosaur ungual, likely dromaeosaurid or caegnagnathid (I lean towards the latter due to the symmetry), scale = 10 mm; B ) unknown ungual; C) unknown ungual; D) unknown ungual

 

Unknown

 

Despite a century of intensive professional research, and a year of self-study to peruse that research, there are still mysteries. There are some things I found for which I don’t know the ID very precisely which I’m comfortable with, but there are a couple of specimens that I have basically no idea what they’re from.

 

A) a germ/developing tooth? It’s mostly hollowed out and looks like an enamel shell; B ) a tooth of something, it’s carinated, the mesial carina twists onto the lingual surface.

 

The closest match I’ve found to unknown ‘B’ is indeterminate microraptorine teeth. It’s a tantalizing possibility but I might try reaching out to professionals since I don’t know much about microraptors.

 

Teeth referred to Microraptorinae indet. or Troodontidae indet. (Averinov et al. 2019)

 

Averianov, Alexander O. et al. “Theropod teeth from the Lower Cretaceous Ilek Formation of Western Siberia, Russia.” Proceedings of the Zoological Institute RAS (2019): n. pag.

 

“Baby” dinosaurs

 

To wrap this all up, I wanted to highlight a few special fossils that represent the early growth stages of a few of the major dinosaur clades present. Fossils of “baby” dinosaurs are generally uncommon, and I’ve been lucky enough to find a handful of them. After comparing these to a few publications and specimens, I can fairly confidently call these young juveniles (a few years old or less). I’m still on the lookout for more species and better examples.

 

The presence of baby dinosaurs tells us that their nests probably weren’t too far away (i.e. they didn’t migrate far to make nests). The morphology and feeding wear on the herbivores suggests they had a similar diet and/or feeding mechanics as adults. 

 

“Baby” dinosaur fossils, US penny for sense of scale (19.05 mm diameter). A) hadrosaurid (Edmontosaurus) tooth; B ) leptoceratopsid (Leptoceratops) rooted tooth; C) troodontid (Pectinodon) tooth; D) dromaeosaurid (Dromaeosauridae) tooth; E) tyrannosaurid (Tyrannosaurus) premaxillary tooth; F) thescelosaurid (Thescelosaurus) premaxillary teeth.

 

Notes:

• Hadrosaurids: Fanti & Tetsuto justify assignment of small hadrosaurid teeth to “babies”, by citing Horner & Currie 1994, who record the largest teeth of embryonic Hypacrosaurus with widths of 4 mm. Adult Edmontosaurus was at least as large or larger than adult Hypacrosaurus, so it seemed reasonable to assume that their neonates were comparable in size if not larger. All of the teeth presented above have widths of about 4 mm. Clearly the worn ones are not embryonic, but these are all comfortably from very young animals.
• Leptoceratopsid: a few “perinatal” leptoceratopsids were reported from the Prince Creek formation of Alaska. Druckenmiller et al. suggest that this leptoceratopsid was comparable in adult size to Leptoceratops gracilis. The tooth I found is marginally larger than those reported in that paper, so it’s reasonable to call it a young juvenile.
• Troodontid: in the description of Pectinodon bakkeri, included are two minute teeth named the paratypes. Carpenter supposed these were from “babies.” The size is also comparable to a perinatal troodontid tooth from the Prince Creek formation (Druckenmiller et al.)
• thescelosaurid: Druckenmiller et al. also refer a couple of thescelosaurid teeth to perinates based on their relative size to those of adults. These teeth are of a similar relative size.
• Tyrannosaurid: a couple of small tyrannosaurid premaxillary teeth have been reported in the literature as perinatal or young of the year, all from species with smaller adult sizes than T. rex. This tooth is the same size as those reported in e.g. Druckenmiller et al. and Funston et al., and thus is reasonably called  a young juvenile. 

 

Funston et al. 2021

 

Druckenmiller PS, Erickson GM, Brinkman D, Brown CM, Eberle JJ. Nesting at extreme polar latitudes by non-avian dinosaurs. Curr Biol. 2021 Aug 23;31(16):3469-3478.e5. doi: 10.1016/j.cub.2021.05.041. Epub 2021 Jun 24. PMID: 34171301.

 

Fanti, Federico and Miyashita, Tetsuto. “A high latitude vertebrate fossil assemblage from the Late Cretaceous of west-central Alberta, Canada: evidence for dinosaur nesting and vertebrate latitudinal gradient.” Palaeogeography, Palaeoclimatology, Palaeoecology 275 (2009): 37-53.

 

Gregory F. Funston, Mark J. Powers, S. Amber Whitebone, Stephen L. Brusatte, John B. Scannella, John R. Horner, and Philip J. Currie. 2021. Baby tyrannosaurid bones and teeth from the Late Cretaceous of western North America1. Canadian Journal of Earth Sciences. 58(9): 756-777. https://doi.org/10.1139/cjes-2020-0169

 

Dinosaur Eggshells

 

Dinosaur eggshells are uncommon. They are found on occasion in the HCF and we do have a fairly complete egg known. Unfortunately, we haven’t found any associated with or attributable to a particular taxon. Instead, the professionals classify eggshell types with “ootaxa.” Not much else can be said about them other than their morphology. The presence of eggshells and young dinosaur fossils together support that their nests weren’t too far from the site of deposition. I’ve so far only found one flake, and at first thought it could’ve been corroded gar skull bone, but set it aside with a gut feeling until I had time to study it and review literature.

 

Identification: Eggshells have a uniform thickness of about 1 mm or slightly more. The outer surface of some types of shell is ornamented with raised, irregular, well-separated nodes. In-between the nodes are few, indistinct, small pores. The inner surface is smooth. My specimen most closely resembles class B eggshells as described in Sahni 1972. Other kinds of egg-layers in this ecosystem (e.g. crocodiles, turtles) do not produce eggshells like this with nodes.

 

A dinosaurian eggshell. Sand grains have lodged in most of the pores. The inner surface isn’t as interesting or distinctive, so I didn’t include it in the graphic.

 

Class “B” dinosaurian eggshells from the Campanian Judith River Formation of Montana. P,R show the outer surface with nodes and pores, Q,S show the smooth interior surface. Figure from Sahni 1972.

 

Frankie D. Jackson, David J. Varricchio "Fossil Egg and Eggshells from the Upper Cretaceous Hell Creek Formation, Montana," Journal of Vertebrate Paleontology, 36(5), (1 September 2016)

 

Sahni, A. (1972). The vertebrate fauna of the Judith River Formation, Montana. Bulletin of the AMNH; v. 147, article 6.

 

Notes on Imaging

 

Because I’ve gotten questions about this in the past, I’ll mention how I produced these images. I used both my phone camera and a nice camera borrowed from family, a Sony a7R II with a macro lens. For microscopic fossils, I used a binocular microscope and positioned my phone camera by hand to the eyepiece to snap photos. For lighting, I used a $15 ring light which provided even soft lighting with adjustable brightness and color temperature. I used a metric scale and a uniform white background (a sheet of printer paper) which contrasted with the dark fossils (this made it easier to remove in editing). To produce most of the “profile” images, I used the built-in Mac app “pages” to mask out the background, scale the fossils, arrange images, and include text. Previously, I used the art app “Procreate” on my iPad, but to save space on it, I decided to try doing the whole process on my computer. This masking isn’t as nice, but it works well enough for my purposes. I’m by no means a photographer, and I’m sure there are things that can be done to improve the quality (e.g. image stacking), but for me these are sufficiently detailed to be informative and visually pleasant.

 

No, I did not photograph every fossil individually, many I did in group shots. It was a pain to physically arrange many small fossils, and it occasionally compromised the focus, but it was far less work than the alternative.

 

Conclusions

 

This personal project is the result of lots of time and money spent over a year collecting, processing, studying, sorting, documenting, and writing. Before I sieved my first spoonful of sand, my hopes were for fish fossils and maybe a shark tooth, I had no inkling of how productive this endeavor would be. Yes, I have been quite lucky, but I’ve also been extremely scrupulous with hundreds of pounds of material; I pick out every crumb of bone, every strange geologic feature, in case later I learn something. My goals going forward this Summer are to better store and display the higher-quality specimens (I’ve been so busy collecting and documenting, they aren’t stored presentably), and find new things - though there’s not much left. At the top of my “to find” list are more baby dinosaurs, birds, paddlefish, and perhaps snake. At this point I don’t have much hope for marine taxa like sawfish, sadly.

 

I’m sure this writeup is not free of error, but I’ve done my best to make it future-proof in being conservative with my IDs and doing my homework. I hope the references compiled here also prove useful. I have considered reproducing the content of this thread in a more professional pdf document, if there’s sufficient interest. I’ve also created an accompanying album that compactly presents the images herein. I don’t believe anything presented in this collection is scientifically novel or important; many micro-surveys of the HCF have been done, more thoroughly and with far more material. But if I’m wrong I’d be happy to talk with any professionals who may be interested. Thanks for reading this far and I hope this proves useful and/or interesting, I’ve certainly had a blast with this whole experience and look forward to learning all I can about the HCF.

 

Link to TFF album, “Hell Creek Formation Microsite”: https://www.thefossilforum.com/gallery/album/3516-hell-creek-formation-microsite/

 

 

All References

 

All of my references are compiled below, roughly in order of appearance. Happy reading!

 

Fastovsky, David E. and Antoine Bercovici. “The Hell Creek Formation and its contribution to the Cretaceous–Paleogene extinction: A short primer.” Cretaceous Research 57 (2016): 368-390.

 

Rogers, Raymond R., and Mara E. Brady. "Origins of Microfossil Bonebeds: Insights from the Upper Cretaceous Judith River Formation of North-central Montana." Paleobiology 36.1 (2010): 80-112.

 

Scholz, Henning, and Joseph H. Hartman. “Paleoenvironmental Reconstruction of the Upper Cretaceous Hell Creek Formation of the Williston Basin, Montana, USA: Implications from the Quantitative Analysis of Unionoid Bivalve Taxonomic Diversity and Morphologic Disparity.” PALAIOS, vol. 22, no. 1, 2007, pp. 24–34. JSTOR, http://www.jstor.org/stable/27670392. 

 

D.W. Larson, D.B. Brinkman, and P.R. Bell. (2010) “Faunal assemblages from the upper Horseshoe Canyon Formation, an early Maastrichtian cool-climate assemblage from Alberta, with special reference to the Albertosaurus sarcophagus bonebed.” Canadian Journal of Earth Sciences. 47(9): 1159-1181. https://doi.org/10.1139/E10-005

 

Meek, F. B.; Hayden, F. V. (1857). Descriptions of new genera of fossils, collected by Dr. F.V. Hayden, in Nebraska territory, under the direction of Lieut. G.K. Warren, US Topographical Engineer; with some remarks on the Tertiary and Cretaceous formations of the north-west, and parallelism of the latter with those of other portions of the United States and Territories. Proceedings of the Academy of Natural Sciences of Philadelphia. 9: 117–148., available online at https://www.biodiversitylibrary.org/page/6330383

page(s): 137-138

 

DeMar, D.G. “An Illustrated Guide to latest Cretaceous Vertebrate Microfossils of the Hell Creek Formation of northeastern Montana.” Unpublished. https://naturalhistory.si.edu/sites/default/files/media/file/fossil-id-guide062812-accessible.pdf

 

Peng, J. & Russell, A.P. & Brinkman, D.B. (2001). “Vertebrate microsite assemblages (exclusive of mammals) from the Foremost and Oldman formations of the Judith River group (Campanian) of Southeastern Alberta : an illustrated guide.” Provincial Museum of Alberta Natural History, Occassional Paper No. 25

Gaudant, Jean . 1992. "Kindleia" fragosa Jordan and "Stylomyleodon" lacus Russell: two amiid fishes from the Late Cretaceous and the Paleocene of Alberta, Canada. Canadian Journal of Earth Sciences. 29(1): 158-173. https://doi.org/10.1139/e92-015

 

Brinkman, Donald B., Michael G. Newbrey, and Andrew G. Neuman. "Diversity and paleoecology of actinopterygian fish from vertebrate microfossil localities of the Maastrichtian Hell Creek Formation of Montana." Through the end of the Cretaceous in the type locality of the Hell Creek Formation in Montana and adjacent areas 503 (2014): 247.

 

Hilton, Eric J., and Lance Grande. “Review of the Fossil Record of Sturgeons, Family Acipenseridae (Actinopterygii: Acipenseriformes), from North America.” Journal of Paleontology 80.4 (2006): 672–683. Web.

 

Estes, R., 1964. Fossil vertebrates from the Cretaceous Lance Formation, eastern Wyoming. University of California Publications in Geological Sciences 49. University of California Press, Berkeley. 

 

Brian L. Hoffman, Jeffrey S. Jensen, Scott A. Hageman "Dental Structure of the Late Cretaceous (Maastrichtian) Guitarfish (Neoselachii: Batoidea) Myledaphus pustulosus from the Hell Creek Formation of Garfield County, Montana," Transactions of the Kansas Academy of Science, 121(3-4), 279-296, (1 September 2018)

 

Gates, Terry A., Eric Gorscak, and Peter J. Makovicky. "New Sharks and Other Chondrichthyans from the Latest Maastrichtian (Late Cretaceous) of North America." Journal of Paleontology 93.3 (2019): 512-30. 

 

Wynd, B.M. & Demar, D.G. & Wilson, G.P. (2020) “Euselachian diversity through the uppermost Cretaceous Hell Creek Formation of Garfield County, Montana, USA, with implications for the Cretaceous-Paleogene mass extinction in freshwater environments.” Cretaceous Research, 113, Article 104483

DOI: 10.1016/j.cretres.2020.104483

 

Gardner, J.D. (2003), Revision of Habrosaurus Gilmore (Caudata; Sirenidae) and relationships among sirenid salamanders. Palaeontology, 46: 1089-1122. https://doi.org/10.1046/j.0031-0239.2003.00335.x

 

Bennett, GE. (2012) Community structure and paleoecology of crocodyliforms from the upper Hell Creek Formation (Maastrichtian), eastern Montana, based on shed teeth. Jeffersoniana. 2012;28:1–15.

 

Jordan C. Mallon & Donald B. Brinkman (2018) “Basilemys morrinensis, a new species of nanhsiungchelyid turtle from the Horseshoe Canyon Formation (Upper Cretaceous) of Alberta, Canada,” Journal of Vertebrate Paleontology, 38:2, DOI: 10.1080/02724634.2018.1431922

 

Gao, K., and Fox, R. C., 1996, Taxonomy and evolution of Late Cretaceous lizards (Reptilia: Squamata) from Western Canada: Bulletin of Carnegie Museum of Natural History, no. 33, p. 1-107. 

 

Longrich, N. R., Bhullar, B. A. S. & Gauthier, J. A. (2012). Mass extinction of lizards and snakes at the Cretaceous–Paleogene boundary. Proceedings of the National Academy of Sciences, USA 109, 21396–21401.

 

Lillegraven, Jason A.. “Latest Cretaceous mammals of upper part of Edmonton Formation of Alberta, Canada, and review of marsupial-placental dichotomy in mammalian evolution.” (1969).

 

Clemens, William A. Fossil Mammals of the Type Lance Formation Wyoming: Marsupalia. Part II. University of California Press, 1963.

 

Clemens, William A. Fossil Mammals of the Type Lance Formation Wyoming: Introduction and Multituberculata. Part I. University of California Press, 1963.

 

Hudgins, Michael Naylor, Philip J. Currie, and Corwin Sullivan. "Dental assessment of Stegoceras validum (Ornithischia: Pachycephalosauridae) and Thescelosaurus neglectus (Ornithischia: Thescelosauridae): paleoecological inferences." Cretaceous Research 130 (2022): 105058.

 

Gregory M. Erickson et al., Complex Dental Structure and Wear Biomechanics in Hadrosaurid Dinosaurs. Science 338, 98-101 (2012). DOI:10.1126/science.1224495

 

Kirkland JI, Alcalá L, Loewen MA, Espílez E, Mampel L, et al. (2013) The Basal Nodosaurid Ankylosaur Europelta carbonensis n. gen., n. sp. from the Lower Cretaceous (Lower Albian) Escucha Formation of Northeastern Spain. PLOS ONE 8(12): e80405. https://doi.org/10.1371/journal.pone.0080405

 

Longrich, Nick. "Small theropod teeth from the Lance Formation of Wyoming, USA." Vertebrate microfossil assemblages: Their role in paleoecology and paleobiogeography (2008): 135-158.

 

Larson DW, Currie PJ (2013) Multivariate Analyses of Small Theropod Dinosaur Teeth and Implications for Paleoecological Turnover through Time. PLoS ONE 8(1): e54329. doi:10.1371/journal.pone.0054329 

 

Currie, Philip J, and David C Evans. “Cranial Anatomy of New Specimens of Saurornitholestes langstoni (Dinosauria, Theropoda, Dromaeosauridae) from the Dinosaur Park Formation (Campanian) of Alberta.” Anatomical record (Hoboken, N.J. : 2007) vol. 303,4 (2020): 691-715. doi:10.1002/ar.24241

 

Sues, Hans-Dieter and Averianov, Alexander. 2016. "Ornithomimidae (Dinosauria: Theropoda) from the Bissekty Formation (Upper Cretaceous: Turonian) of Uzbekistan." Cretaceous Research, 57 90–110. https://doi.org/10.1016/j.cretres.2015.07.012.

 

Evans, D.C., Larson, D.W. & Currie, P.J. A new dromaeosaurid (Dinosauria: Theropoda) with Asian affinities from the latest Cretaceous of North America. Naturwissenschaften 100, 1041–1049 (2013). https://doi.org/10.1007/s00114-013-1107-5

 

Carpenter, K. (1982). "Baby dinosaurs from the Late Cretaceous Lance and Hell Creek formations and a description of a new species of theropod". Contributions to Geology, University of Wyoming. 20 (2): 123–134.

 

Thomas M. Cullen, Brian L. Cousens; New biogeochemical insights into Mesozoic terrestrial paleoecology and evidence for omnivory in troodontid dinosaurs. GSA Bulletin 2023; doi: https://doi.org/10.1130/B37077.1

 

Druckenmiller PS, Erickson GM, Brinkman D, Brown CM, Eberle JJ. Nesting at extreme polar latitudes by non-avian dinosaurs. Curr Biol. 2021 Aug 23;31(16):3469-3478.e5. doi: 10.1016/j.cub.2021.05.041. Epub 2021 Jun 24. PMID: 34171301.

 

Fanti, Federico and Miyashita, Tetsuto. “A high latitude vertebrate fossil assemblage from the Late Cretaceous of west-central Alberta, Canada: evidence for dinosaur nesting and vertebrate latitudinal gradient.” Palaeogeography, Palaeoclimatology, Palaeoecology 275 (2009): 37-53.

 

Gregory F. Funston, Mark J. Powers, S. Amber Whitebone, Stephen L. Brusatte, John B. Scannella, John R. Horner, and Philip J. Currie. 2021. Baby tyrannosaurid bones and teeth from the Late Cretaceous of western North America1. Canadian Journal of Earth Sciences. 58(9): 756-777. https://doi.org/10.1139/cjes-2020-0169

 

Frankie D. Jackson, David J. Varricchio "Fossil Egg and Eggshells from the Upper Cretaceous Hell Creek Formation, Montana," Journal of Vertebrate Paleontology, 36(5), (1 September 2016)

 

Sahni, A. (1972). The vertebrate fauna of the Judith River Formation, Montana. Bulletin of the AMNH; v. 147, article 6.

Edited May 26 by ThePhysicist

[Mikrogeophagus]

This is awesome!!! Just gotta say congratulations first on the finds and second on the thorough, yet smooth writing. Comprehensive reports like these are a joy to read and really present an understanding of a site like no other methodology. I am sure this will be a useful resource for all hunters, not just searching the Hell Creek, for many many years to come. Thanks!

[ThePhysicist]

2 hours ago, Mikrogeophagus said:

This is awesome!!! Just gotta say congratulations first on the finds and second on the thorough, yet smooth writing. Comprehensive reports like these are a joy to read and really present an understanding of a site like no other methodology. I am sure this will be a useful resource for all hunters, not just searching the Hell Creek, for many many years to come. Thanks!

That's high praise from you, I appreciate it! It's been a long journey producing this but I've enjoyed every step.

[ClearLake]

This is fantastic!!  Well done!!  I can’t wait for more of the pictures to load on my phone with my (apparently) slow connection. I’ve never collected the Hell Creek or really anything similar. This is really outside my wheelhouse, but maybe that’s why it looks so interesting. Thank you and I look forward to reading more of the report. 

[Jared C]

Truly fantastic write up. Saving it to my favorites tab

[jpc]

Holy Guacamole!!!!  

What an excellent report/synopsis/guide.  

This is an amazing almost error-free (I really hard a hard time finding any... see below) well, written, well illustrated, well referenced report.  I give you a gold star on your forehead and suggest to the mods that this be given a pin.  

 

A few quick questions, and maybe the answers are in here and I glossed over them.  Is this material all from one microsite?  And how many bucketfuls/bagfuls/pound/kilos of matrix did you collect?

 

Your results are very similar to mine, but there is variability from one site to another.  For example, here in Wyoming's Lance Fm, rays (Myledaphis) are just a part of the fauna, but in one of my sites in Montana, rays are THE most common fossil by far, which seems to be similar to your results.

 

The one thing that may need re-identifying, may also be a trick of the light. In your soft-shelled turtle pix, the upper left one looks like it is coated with small raised dimples.  Or is that a population of small divots?  If they are raised it will be Basilemys.  Again, lighting... 

 

In your Dromaeosaur illustrations, you've got the same tooth (D in both figures) IDed as two different things Zapsalis and Acheoraptor.  Surely a typo.  

 

I also have one of those lower p4 with only two cusps on the trigonid (raised set of three cusps on a mammal lower molar).  I have also had a heckuva time I had a hell of a time IDing it.  Thanks for the hep in IDing it.

 

I have done a lot of screening of Lance and Hell Creek Fm material and am now looking for good Campanian sites in Wyoming for a slight shift, but also focusing more on some Eocene sites in search of mammals.  Some of the Eocene sites are pretty rich in snake verts, which are a thrill after finding only a few in the Maastrichtian.

  

Thanks for posting this on a holiday (Memorial Day here in the states) so I have to read it.  

 

Again... Excellent work all around.  

 

jpc

 

[ThePhysicist]

23 hours ago, ClearLake said:

This is fantastic!!  Well done!!  I can’t wait for more of the pictures to load on my phone with my (apparently) slow connection. I’ve never collected the Hell Creek or really anything similar. This is really outside my wheelhouse, but maybe that’s why it looks so interesting. Thank you and I look forward to reading more of the report. 

Thank you! I tried to manage the image sizes without compromising resolution, but for something like this any effort only does so much.

 

Sans the dinosaurs, the HCF is very similar to modern ecosystems in the southern US. That for me makes it all the more interesting to see fossils of living animals I grew up around, namely gar fish.

 

21 hours ago, Jared C said:

Truly fantastic write up. Saving it to my favorites tab

Thank you! I'll consider it an honor .

[ThePhysicist]

9 hours ago, jpc said:

Holy Guacamole!!!!  

What an excellent report/synopsis/guide.  

Thank you! It's great to hear that from a professional.

 

9 hours ago, jpc said:

A few quick questions, and maybe the answers are in here and I glossed over them.  Is this material all from one microsite?  And how many bucketfuls/bagfuls/pound/kilos of matrix did you collect?

Yes, it's all from one site. In total, close to 500 lbs, 50 gal by my guess.

 

9 hours ago, jpc said:

The one thing that may need re-identifying, may also be a trick of the light. In your soft-shelled turtle pix, the upper left one looks like it is coated with small raised dimples.  Or is that a population of small divots?  If they are raised it will be Basilemys.  Again, lighting... 

They're dimples which are definitionally depressions in the surface, so I believe my primary ID stands.

 

9 hours ago, jpc said:

In your Dromaeosaur illustrations, you've got the same tooth (D in both figures) IDed as two different things Zapsalis and Acheoraptor.  Surely a typo.  

Not a typo, it's a "Zapsalis-morph", which has recently been shown to be anterior dromaeosaurid teeth (seen in Saurornitholestes). Since Acheroraptor is most recently considered a saurornitholestine, I suggested it's likely Acheroraptor. I note it as Zapsalis in the first image since you see the name come up occasionally even though it's defunct.

 

9 hours ago, jpc said:

also have one of those lower p4 with only two cusps on the trigonid (raised set of three cusps on a mammal lower molar).  I have also had a heckuva time I had a hell of a time IDing it.  Thanks for the hep in IDing it.

Sure thing, it was quite strange!

[old bones]

This is fantastic! I am going to have read it over and over to absorb all the wonderful information and awesome visuals!

[MarcoSr]

Incredible post.  Very informative.  Great specimens and great pictures.  It will take me a good while to absorb the information presented.  Admins, this post should be pinned.

 

Marco Sr.

[ThePhysicist]

On 5/27/2024 at 7:23 PM, old bones said:

This is fantastic! I am going to have read it over and over to absorb all the wonderful information and awesome visuals!

Thank you! I've had to read it over and over in writing it, so that sounds fair haha!

 

On 5/28/2024 at 5:02 AM, MarcoSr said:

Incredible post.  Very informative.  Great specimens and great pictures.  It will take me a good while to absorb the information presented.

Thank you! Knowing your extensive experience with micros that means quite a lot to me.

[tonno.tethys]

wow this is super interesting! too bad I'm so far from hell creek... does anyone know if it is possible and where to buy "raw" sediment to try to find these micro/macro fossils?  

[ThePhysicist]

19 hours ago, tonno.tethys said:

wow this is super interesting! too bad I'm so far from hell creek... does anyone know if it is possible and where to buy "raw" sediment to try to find these micro/macro fossils?  

Glad you enjoyed! Per forum rules, we do not discuss sellers.

[Alex S.]

This is an excellent resource thank you for going through all the work to out it together. I also vote that it be pinned. I love micromatrix I  need to get going through mine although I only have around a gallon and a half.

[ThePhysicist]

On 5/31/2024 at 3:19 PM, Alex S. said:

I love micromatrix I  need to get going through mine although I only have around a gallon and a half.

Depending on the deposit, you might be surprised by how much diversity can be captured even in a small volume. Be thorough.

[Alex S.]

It's Hell Creek mainly mainly from excess matrix from jackets. I have just done some preliminary sieves and kept everything from each stage. I'm mainly waiting on a better scope before I go through it all.