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Fox Hills Formation of North Dakota


Thomas.Dodson

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Thomas.Dodson

I've been posting Fox Hills Formation fossils from a recent trip but I feel that those are a poor representation of the often spectacular preservation and diversity of the Fox Hills Formation. Because of that I've decided to post some of my better Fox Hills specimens from North Dakota.

 

We'll start with some lovely ammonites. Jeletzkytes nebrascensis is common throughout the Fox Hills Formation in the Timber Lake Member (perhaps a bit less so in North Dakota) and is a typical flagship species for the formation. This microconch from Emmons County is the largest complete J. nebrascensis I've collected. The slash mark is an unfortunate result of removing an ammonite from directly atop this one before I was aware of this one. I think it turned out well despite that.

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Thomas.Dodson

Hoploscaphites sp. are also common in the Fox Hills. This Hoploscaphites nicolletii is the largest I've collected and was compressed/smashed after burial. The infill sediment makes it an interesting specimen.

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Some smaller Hoploscaphites nicolletii from the same site.

 

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A mostly complete Hoploscaphites comprimus from the same Timber Lake exposure as the Jeletzkytes. I'm going to call this "Timber Lake Exposure 1" since many great specimens come from the site and I'll be posting a lot of them.

 

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Thomas.Dodson

Discoscaphites conradi microconch.

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Discoscaphites conradi macroconch.

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A Discoscaphites gulosus and a juvenile scaphitidae ammonite from Timber Lake Exposure 1.

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Thomas.Dodson

More H. comprimus from Timber Lake Exposure 1.

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Sphenodiscus lenticularis is one of my favorite ammonites. For those who haven't seen these they are crazy thin. Think coin thickness. This specimen has the complete living chamber which is rather rare in specimens I've collected. A sliver between the living chamber and the phragmocone has detached on the negative side showing how thin and fragile they are.

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These are more typical of Sphenodiscus I collect in North Dakota.

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To be continued.

 

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Beautiful ammonites. :b_love1:

I love the colours present in these specimens and know that the camera doesn't properly capture the full effect. 

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Uncle Siphuncle

Texas has some coterminous occurrences of several of these genera, preservation just not as sexy.

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Beautiful little Spheno.   Ive found a lot of these in years past, but never with a complete living chamber.  Nice find that one!

 

RB

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Wonderful fossils. :) 

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I haven't been up there in nearly a decade. I think I know where my day three stop is going to be for my 2021 excursion. When I was with the ACoE, I never got enough spare time to hunt the sites.

 

Thanks for sharing such wonderful specimens and reminding me of a spot to put on the excursion list.

 

I've said it before and will say it again, ammos are my favorite extinct invert.

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thelivingdead531

Absolutely beautiful! The colors are magnificent on those ammonites! 

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Thomas.Dodson

Jeletzkytes spedeni from the Trail City Member is something of a chase species for me as I've only found this single small microconch and pieces of the living chambers. The Trail City is poorly exposed in North Dakota which contributes.

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Immature Scaphitidae make up a very large portion of the concretions of Timber Lake exposure 1. Think 50-70 complete individuals in a football sized concretion.

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Thomas.Dodson

Pereiopod elements from decapods are one of the fossils that make Timber Lake exposure 1 my favorite site. I haven't found them elsewhere yet in the Fox Hills. These likely belong to Raninella oaheensis based partly on the identification of an elongate dorsal carapace from the site. I apologize for the lack of scale, I find it difficult to focus on these smaller specimens. Specimen one is about 12 mm, specimen 2 is about 11 mm, and the dorsal carapace is about 22 mm.

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Crassostrea glabra is the most common oyster of the Fox Hills in North Dakota although pellucida and subtrigonalis are also present. In times past these were said to "festoon the surface of pasture lands". They are still commonly found on roadcut surfaces, land, and any areas of erosion.

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Gervillia recta is very abundant in the Trail City Member. You don't even time to prepare all of them. The spent concretion pieces make a nice and attractive gravel/weed cover.

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Gervillia/Pseudoptera subtortuosa is less common but just as beautiful.

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Thomas.Dodson

The decapod trace burrows of Ophiomorpha sp. are by far the most common fossil of the Fox Hills Formation in North Dakota. Some of these form massive networks in bedrock cuts. Many of the fossils are straight fragments. This is my most complex one.

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Dentalium sp. are common in the Fox Hills of North Dakota but are generally very small. This specimen comes from a site I like to call "The Land of Giants" because of the large sizes of specimens that are generally much smaller elsewhere in the formation.

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This Oligoptycha concina absolutely dwarfs specimens from other sites that are typically a fraction of the size. I could hardly believe they were Oligoptycha concina when I found them.

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My larger specimens of Cucullaea shumardi also come from this site but they are giants to begin with.

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Thomas.Dodson

Ammonite aptychus, often paired, make up another large portion of the concretions at Timber Lake exposure 1. The aptychus here tend to shine a little like the ammonites.

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Vertebrate material usually consists of scales in the Fox Hills.

Ctenoid scales of this type are the most common at Timber Lake Exposure 1.

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Occasionally other vertebrate material is found. I don't have much hope of identifying this beyond the broad scope but it's a nice Fox Hills addition nevertheless. Eventually something more substantial might show up. I can't really complain with the Fox Hills material I've collected.

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Feldman (1967) did a good job documenting the Bivalvia of the Fox Hills Formation in North Dakota. There are still multiple rare specimens he described that I hope to one day come across. In the meantime, here's something that was never reported from the Fox Hills of North Dakota at all, one of two Cuspidaria sp. Timber Lake exposure 1 once again demonstrating what a cool site it is. This one came from the overlying sandstone layers. The other specimen came from the concretions.

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Thomas.Dodson

Tellinimera scitula is a common bivalve in the Fox Hills Formation but one of my favorites. Even among the great preservation in the Fox Hills Formation some stand out with fantastic colors and even show the color bands and rays like in modern Tellinids.

 

 

 

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Thomas.Dodson
18 hours ago, jpc said:

These have been some great fossils.

Thanks, the Fox Hills Formation has always been one of my favorites, in part because it was one of the first formations I began to collect in when I was a kid. I've got lots more really nice specimens but a lot of them get smaller so I'm working on improving my macro photography before I try posting them.

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  • 3 weeks later...
Thomas.Dodson

I've been meaning to continue this and have photographed multiple more Fox Hills stuff but I frequently find I don't capture the small fossils well on camera, discard the photos, and try again later. I figured I'd post some in this round.

 

Corals are poorly represented in North American Cretaceous deposits and the only one I've found in the Fox Hills of North Dakota is a Micrabacia sp. These tiny corals are also rare here and I've only found them at "Timber Lake Exposure 1".

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Grammatodon (Cosmetodon, Nemodon) sulcatinus is a small bivalve rarely found in the state and recorded from only a single locality where the Trail City outcrops. I've collected a couple adult specimens from this site but the pictured specimen below is a tiny individual that came from the Timber Lake Exposure 1. Nevertheless, there is nothing else similar from the Fox Hills of North Dakota so it was easily recognizable. 

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The gastropod Graphidula culbertsoni has been the most common high-spired gastropod found in the Fox Hills of ND for me. Large individuals like the one pictured are quite rare but smaller adults between ~2-3 cm are common. Taxonomy of these is confusing, partly because of juvenile characteristics that only appear on immature specimens such as ribbons crossing the fine spiral lines that are lost at maturity. Inconsistent numbers of columnellar plaits are also confusing among species of Graphidula and the closely related Piestochilus species also found in the Fox Hills. I prefer to separate them by apical angle and whorl convexity as Erickson (1974) attempted. Frankly these need a taxonomic overall based on a large sample size.

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Outer shell pattern of a mature individual.

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Thomas.Dodson

Piestochilus have more flattened whorls and a distinctly different apical angle like in these Piestochilus scarboroughi from another Timber Lake site. Still, there's some intergrade and there are multiple species of both Piestochilus and Graphidula present in the Fox Hills.

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The common gastropod Drepanochilus evansi has interesting extensions of the outer lip. These frequently break off before fossilization. drepano.png.d355bd8b3bc48c676bfc4bbf4a67a6b0.png

Here is one with good outer shell preservation but is missing the extended outer lip.

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This tiny incomplete gastropod might be what was reported by Erickson as Amuletum minor.

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Speaking of small gastropods, I have a lot of trouble photographing the lovely patterns on the common Cylichna scitula.

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Thomas.Dodson

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The tiny Corbulamella inornata is most common at the Trail City exposures.

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Crenella elegantula is a species I rarely come across. This specimen came from the Trail City Member.

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Nucula sp. are my favorite bivalves in the Fox Hills. The outer shell rarely remains on the shell, instead sticking to the concretion. Because of this the nacreous layer is readily exposed on most specimens.

A large Nucula planomarginata from the Trail City Member.

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The outer shell layer and nacreous layer of a Nucula planomarginata from Timber Lake Exposure 1 adhered to a concretion.

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Thomas.Dodson

A small Nucula planomarginata that has most of the outer shell. 5fe3ba08be48f_Nuculapl.png.4e9e11b47af8d61688b62616d2c21572.png

A small Nucula cancellata showing off the lovely teeth.

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I've only found Rhombopsis subturritus at Timber Lake Exposure 1.

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This appears to be the same as the single specimen assigned to Cryptorhytis flexicosta? by Erickson. Also found at Timber Lake Exposure 1. Attempting to show the 2 broad collumnar plaits in the second pic, one of the diagnostic characteristics.

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A "normal" shaped Pteria linguaeformis. These take on odd shapes a lot of the time.

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The gastropod Semitriton buccinoides, only found in the Trail City Member and Limopsis striatopunctatus. Limopsis is very common in the Trail City Member and is best distinguished from the similar Protocardia subquadrata by it's punctate surface and lack of scalloped margins.

 

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A worn Protocardia subquadrata showing the characteristic scalloped margin and Ellipsoscapha cf. E. minor.

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The gastropods Spironema tenuilineata and Vanikoropsis nebrascensis from the Trail City Member. These similar species are thought to be possible synonyms.

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Indeterminate Margaritidae snails are common at some sites in the Fox Hills. Erickson never assigned his specimens to a genus citing lack of umbilical detail on his specimens. Some of mine do have well defined umbilical detail and are probably either Atira or Margarita.

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Species of the genus Euspira are cool and common in the Fox Hills. I most often collect Euspira rectilabrum and Euspira obliquata (pictured) and occasionally Euspira dakotensis (only Trail City). There's a Euspira subcrassa reported which I haven't yet found. Apparently these are sexually dimorphic with differences in spire height.

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The apparently very rare Serrifusus dakotensis from a recent trip is one of my favorite gastropods. A complete shelled specimen would be nice considering its rarity it is still great.

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  • 4 weeks later...
Thomas.Dodson

A little stir crazy from the snow I have been looking for fossils to work with in my collection. Most have been prepped already but there was one partial concretion piece that was adorning my yard sizeable enough to work down some more. It was clearly from my Trail City site and I wasn't expecting much since it wasn't a sizeable piece. I was surprised to find 3 nice ammonites clumped together in it, especially since ammonites are rarer from this locality. Because of the variety and close positioning of them I decided to do things a little differently and prepare them in the display orientation they were in the concretion. In retrospect I should have taken more pictures, especially before starting the preparation.

 

I had to stabilize the outer shell layers which were rather powdery as they sometimes are from this site. Most of the shell took on a yellowy finish after the paraloid but it's better than all the shell sloughing off.

 

This is a picture of the "main" part of the concretion I decided to use as a stand. In this pic I already prepared the ammonites from this half and then reoriented them as they were in the concretion. The larger one fits into the negative like a key because of the perfect fitting umbilical matrix stuck to the negative. For the smaller one I used a little CA glue to mount it back in position. Note the part of shell from the third ammonite.

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Here's a picture of the third ammonite before being prepared. I did this one a day later than the first two which is why I ended up taking a pre-prep picture. At least I got one pre-prep picture.

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