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  1. Mikrogeophagus

    Squalicorax falcatus, Atco

    From the album: Austin Chalk

    Squalicorax falcatus, DFW Coniacian, Cretaceous Feb, 2023 The biggest squali in my collection so far!
  2. The weather's finally warming up here in DFW, and with that, it's time to move on from the comforts of dry land and return to the ways of creek stomping. These past few months, I've been mostly hanging around cuts and construction sites within the Washita Group, and to be honest, I've gotten a little sick of it. During that period, I steadily accrued a sizable list of potential Eagle Ford and Atco locations within the metroplex, and I was itching for the opportunity to finally go and check them out. Yesterday, I circled a few spots on the map and hit the road. Well, the first couple of sites were more or less complete duds. Stop 1 was situated in the Turner Park Member of the Britton. Lots of cool stuff can be found here and it's one of the more prettier formations, but I'm still trying to figure it out. I only spent about 30 minutes there, and nothing really impressed me. Nevertheless, I was at least rewarded with my first ptychodus from DFW (yeah it took awhile). Stop 2 was a famous site within the Camp Wisdom Member of the Britton. There were some interesting cephalopod specimens to be had, but nothing worth taking home. I did not lose hope, though. I knew that my third site was the most promising of the bunch and I accordingly saved most of the day for it. Stop 1 in the Turner Park, and my first ptychodus from DFW (P. anonymous) The Atco lies just above the Arcadia Park Formation of the Eagle Ford Group in DFW. It's famous for being densely packed with a diverse array of vertebrate material dating to the Coniacian, mostly concentrated within a thin layer dubbed the "Fish Bed Conglomerate" just at the contact of the Eagle Ford and Austin groups. The key to finding this layer is to look for matrix that is highly concentrated in phosphatic pebbles and fossils. Down in Austin, I think it gets a bit overshadowed by the Eagle Ford. In DFW, however, I would say the Atco reigns supreme. After a decent drive and trek, I stepped into the creek and began my descent through the Austin Chalk in search of this coveted conglomerate. It was difficult to tell where exactly I was stratigraphically since the Arcadia Park seems to be a bit calcareous whereas the Austin Chalk can be a bit marly. Where the calcareous marl ends and marly chalk begins is tougher to differentiate in practice, especially for someone less experienced like me. I eventually reached a large gravel bar and decided to pause the walking and have a look for any clues. I didn't find anything out of the ordinary in my initial scan, and almost picked up my backpack to move on. However, I took a moment to take a closer look at what I had first subconsciously written off as concrete. In this chunk of rock, I saw hundreds of tiny rounded phosphatic pebbles. Once my eyes reached the edge of the block, I spotted the unmistakable serrated blade of a Squalicorax falcatus tooth. There was no doubt, this was Atco matrix! The material was noticeably greyer than I had expected. Down in Central TX, the Atco is about as white as the rest of the overlying chalk. With all of the odd bits and bobs intermingling with the grey rock, it really does look like something manmade. I pulled out the rock hammer and began searching the bar for more chunks of fish bed conglomerate. It's amazing the things your eyes can miss when you unknowingly tune things out. There were very obvious shark teeth encased in many of the rocks I had walked by earlier. I collected several larger pieces and sat down to begin extracting teeth. Found my nicest shark vert yet. Unfortunately, it was super fragile and lots of it broke apart in cleaning. My first oddball tooth from the Atco. It has the shape of Cretalamna appendiculata (in the strict sense), but the presence of labial striations pushes me towards a posterior tooth of Cretodus crassidens. It also notably has doubled cusplets on one side. That same tooth post extraction. It broke in half by the time it got home, so I'll be doing a bit of consolidating. Funky little guy. There were some very large slabs of Atco conglomerate washed out atop the gravel bar. I did some hammering to break them into more manageable chunks so I could rinse them in the flowing creek. As I split one of the large slabs in half, I let out an annoyed sigh as I saw a decent Cretalamna appendiculata tooth crumble from the point my hammer had hit the stone. I tried to push that misfortune out of my mind as I perused across the newly exposed surface for any other teeth. I quickly spotted some fine serrations poking out of a chip of matrix that had just come loose. It was a Squalicorax falcatus doing its best chameleon impression. Please don't break please don't break Voila! By far the largest Squalicorax in my ever-growing collection! Florida megs better watch out... My constant hunt for micros at home adequately prepared me to keep an eye out in the field. I was able to spot a couple of Ptychotrygon triangularis oral teeth throughout the day. I also managed to find a mediocre Scapanorhynchus raphiodon and my first decent Ptychodus whipplei! Managed not to lose it in the gravel. Ptychotrygon triangularis Lots of beat up Scapanorhynchus raphiodon that day Ptychodus whipplei. The bits and pieces I have from Austin look like they were crapped off a cliff by a coyote as some Texas fossilers like to say. After getting a nice sunburn, I decided to get up and explore more of the area to perhaps find a source for this matrix. I spotted a little tributary that seemed promising and had a gander. Some outcrops have a beauty that only fossil hunters can truly appreciate... You who are reading this, I know your mouth is watering A little ways farther, the source is found. As I walked up the small feeder creek, I periodically inspected the pieces of fish bed conglomerate that were scattered in the way of the flowing water. One ball of matrix had an unsuspecting appearance, but something about it wouldn't let me leave it alone. There was what initially seemed to be some part of a bivalve erupting from it, but the color and texture gave off enamel vibes. After hammering off some chalk, I still couldn't figure it out. I eventually extracted the entire thing. It was extremely smooth and came to an edge at the top. The surface was mostly bluish gray and semi translucent. It took a second for the cogs in my brain to start working and realize I'd seen something very similar before. @Jared C and I have been recently discussing Hadrodus, and, of course, one of his best discoveries is a large fragment of Hadrodus hewletti of which shares many visual characteristics with the object in my hand. I was excited to realize I was holding the tooth to a gargantuan pycnodont fish. Just after extraction Occlusal view and side pics For scale. Stay tuned for the identity of this monster After this discovery, my stomach growled, signaling it was about time to head back. This was only my first excursion in the Atco of North Texas, and it had already proven to be one to remember. For sure, this will be a site to return to. As I walked along the banks towards my exit, my eyes were still honed in on the ground as is the curse set upon every fossil hunter. I usually don't find anything on my return walks, but I was delighted to see the sheen of black enamel poking out of some Atco chalk just several feet above the fish bed conglomerate. I popped it out and quickly identified it as Ptychodus, though the species I was unsure of. At the moment, I think it is P. atcoensis as it seems to be a good match with a specimen in Hamm's paper on the Atco. It's got radiating ridges and a marginal area similar to some P. anonymous. That paper mentions Meyer (1974) suggested that the taxon could be transitional between P. mortoni and P. anonymous and I certainly understand that reasoning. It's a little beat up, but that's a rare species and a special one. In situ Radiating ridges and concentric ridges in the marginal area as expected for P. atcoensis Once I got home, I began researching more on my fish tooth to try and pin an ID. My initial idea was that it could be a Hadrodus incisor like what Jared had in his collection based on size and coloration alone. Jared was quick to point out that the morphology differed greatly between my tooth and most incisors. This was a valid hole in the argument and I went back to the drawing board. The tooth was most certainly pycnodont in origin, but the world of pycnodonts is much deeper than most people realize. When examining the edge of the tooth I noticed a characteristic I couldn't come up with a name for until I saw it in one of the papers on Hadrodus Jared had shared. "Papilla-like tubercles" were the things lining the edge, and thankfully the author of the paper offhandedly brought up another genus of pycnodont that shared this trait: Acrotemnus. After some searching, I found a recently published paper by Shimada on a newly discovered specimen of Acrotemnus streckeri from Big Bend in the Ernst Member of the Boquillas Formation. And wouldn't ya know it, Hamm stated that the Ernst Member can be correlated with the Atco Formation (though I should mention a discrepancy in that Shimada places the Ernst Member in the Turonian and not the Coniacian which Hamm asserts the Atco + Ernst to be). The Acrotemnus paper had some high quality images of the dentition of the specimen, and I found the most similarity in size and morphology with the prearticular teeth of their fish. The Shimada paper mentioned that most pycnodonts are small, only reaching about 25 cm in size. To people who are unfamiliar with pycnodonts, these teeth may not look all that crazy, being measured only as 1-2 centimeters . However, scaling the body with the size of the dentition shows that Acrotemnus streckeri reached lengths of at least 1 - 1.3 meters, making it some of the largest pycnodonts to exist at the time! This definitely shattered my preconceived notions about pycnodont fish. Already, the Atco has proven to be one of the most interesting formations in North Texas. This site is a bit of a laborious drive for me, but I'm certain many future adventures will be had and many more fascinating discoveries with it. Thanks for reading!
  3. Mikrogeophagus

    Squalicorax falcatus, Bouldin Flags

    From the album: Eagle Ford Group

    Squalicorax falcatus, Travis Co. Cenomanian, Cretaceous Oct, 2022
  4. A couple of weeks ago, @Jackito, his son, and I took a trip out to one of his favorite Eagle Ford sites. For those of you who are familiar with Carter's posts, this was once the famed location of the so-called "giving rock", so the bar was set high for the day. I've come across some of Austin's eagle ford material in the past, but it was always only the leftovers of what had been washed through miles of rushing creek water. This was my first time getting to poke through the source material, so I was eager to see what could be found. The water was low and the temperature mild. I was thankful I wouldn't have to suffer trudging around in soggy shoes. As we walked beside the creek, Carter explained the various layers and where the best stuff could be found. He pointed out the notable spots where things like pseudomegachasma and pliosaur teeth had been dug up. I knew to not get my hopes THAT high up, but it was certainly a good motivator to stay attentive and expect the unexpectable. It took me a while to get the hang of pinpointing which slabs were best to open and how. Carter was nice enough to share some of his finds, and I must admit, not everything pictured below was necessarily first spotted by me . I was quickly surprised by the sheer number of shark teeth we started finding. Being the completionist that I am, I would immediately try to excavate every tooth I found. Carter advised me that simply bringing the matrix home and processing it there would be the most efficient use of time which I have come to agree with. Every tooth had fantastic preservation and would often pop right out of the shale (though not necessarily in one piece). The Ptychodus teeth were the most mesmerizing. They basically broke off without a speck of matrix still attached and had a beautiful shine. Thankfully, they were also robust and rarely fell apart. A decently sized Ptychodus still in matrix The amount of Cretoxyrhina to be found was also staggering. Unfortunately, they required a little bit more delicate prep than what I had to offer in the field, so my ratio of broken to unbroken teeth was higher than I'd like to admit. In my defense, I managed to lower that ratio as the day progressed. Squalicorax was also a common sight along with various fish teeth. Carter's son managed to find some turtle material... that was still alive and may or may not have come from out of the stream . For most of the hunt, Carter and I had some nice discussions on things to be found here in Austin along with various chats about life. The hours seemed to fly by so fast, it wasn't long until Carter and Jack had to head on out. They'd been wanting to find some mosasaur material for a while, so I sent info on one of my favorite sites (the place where I came out with 4 mosasaur verts in a day). Hopefully we'll get to hunt together over there some time in the near future. I stuck around as I had a couple hours to kill before needing to drive to a friend's birthday. The rest of the time was spent doing more of the same. I managed to come across a huge Cretodus tooth, but the root was unfortunately nowhere to be found. I also started gathering some of the leftover matrix for later processing for microfossils. The layer was just so rich, how could there not be something cool to find? I filled up a couple Ziploc bags with the stuff and made my way out, thinking of ways I could clean this while residing in a college dorm. The richness of fossils in the matrix. This piece was a little too stony to break down though. Might try vinegar. Suffice it to say, I figured out a way to clean it without clogging the communal sinks, but it's a slow process. Though, I must admit, it's nice to come home each day to a cup's worth of dried micro matrix ready for screening. In only my first batch, I found something I think is pretty amazing. What was at first just a shiny little speck, upon closer analyzing, may, in fact, be a tiny coniasaur tooth! It has that characteristic bulging crown that is instantly recognizable. Hopefully I'm not jumping the gun on this one. A couple rounds later, and many many puny Ptychodus teeth, I managed to spot what appeared to be the tooth plate to a Pycnodont fish or something similar. After some delicate cleaning and lots of paraloid, it's still a little bit scuffed, but there are definitely some little round bulbous teeth in close association. The tooth plate before and after cleaning. Can anyone confirm if it's Pycnodont? There was plenty bony fish and shark material. Interspersed within them were some that eluded my identification (including mayyybe Paraisurus?). I've got plenty of matrix to still go through, so I will post updates if anything cool is found. For now, here are some pictures summarizing the finds: Please excuse the hand pics. It's just that the details come out better on a slightly darker surface as opposed to white paper. Closeups of Coniasaur(?) Tooth L to R: Bony bits, "Coniasaur" tooth, and "Pycnodont" tooth plate The best of the Ptychodus and a close up of the smallest one. The bottom left is smoothed over. Is this maybe feeding damage? Also, any ID for species is much appreciated : Cretoxyrhina mantelli. My favorite is the fat one on the left Best of the Squalicorax falcatus. Right two are a little strange. Possibly symphyseal? Best of Scapanorhynchus and huge rootless Cretodus (hard to see in pic, but its got the wrinkling): Paraisurus? I saw that genus mentioned in a Shawn Hamm publication on the Atco and thought it could be a match. The roots are very skinny on both specimens and the teeth seem vertically stretched. The larger tooth on the left initially appears to be missing half the root, but it is actually nearly complete. The only break is a tiny portion of the root at the very top. The right specimen is very fragmented. No signs of cusps nor nutrient groove on either one. Cantioscyllium orals and Sawfish Rostral Teeth: L to R: Enchodus, Protosphyraena, and Pachyrhizodus Some oddballs. The left is a fragment of some sort of multi-cusped shark tooth. The middle is a a segment of some barbed material that seems similar in appearance to the fishy bits found in the matrix. The right specimen is a shiny crescent shaped thing that I have found in other micro matrixes from Moss Creek and POC. Never kept them, but now I'm curious after finding them again: Thanks for reading!
  5. X-fish

    Squalicorax falcatus

    From the album: Kansas Cretaceous

    20mm on the slant Collected in the Smoky Hill Chalk in Northeast Lane Co. KS

    © Isaac Fox

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