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Took a short visit today to my Basal Atco site for the third time. Seems like every visit yields something new and totally unexpected (first visit = Acrotemnus prearticular tooth, second visit = huge assoc. fish verts, and now these). I'm fairly confident both of these are reptilian, but unfortunately I don't know much about identifying tetrapods. The first specimen I found is now my only non-Campanian mosasaur tooth. It's quite small (1 cm tall) and broke into 3 pieces, but the b72 seems to have done the job in making it presentable. Not amazing quality as expected for the Basal Atco, where much of the material is reworked. I'm not completely familiar with the genera present in the earliest Coniacian. I have read about a chunk of Tylosaurinae maxilla being found near if not in the Basal Atco of Grayson county and the subfamily is thought to have started in the Lower Coniacian altogether. I want to say Russellosaurus made it to the Atco although I believe my tooth is a little large for this ID. I think Clidastes was also around in the Coniacian, although not sure how early. And there's a lot of genera I am not mentioning, so hopefully someone in the know can fill in. The tooth itself seems to have both a mesial and distal non-serrated carina. The enamel isn't faceted as far as I can tell. I know it's not much to go off of and a precise ID is unlikely, but my hope is to at least cross off some of the genera that don't fit the description with yall's help. Mosasaur tooth (1 cm tall) Going from a relatively old mosasaur, the second specimen is a surprisingly young Coniasaurus (or so I think). This might be surprising to some, but Conisaurus is found beyond the Cenomanian. It actually has been documented to extend through the Coniacian all the way into the Middle Santonian (though the documentation is few and far between I must admit)! In other words this is a rare sort of find, but not necessarily unheard of. I don't believe any species have been named extending past the Turonian, so this may be an undescribed species. My specimen has that classic bulbous shape as well as textured enamel. It sure pays to look closely at every chunk of matrix. Coniasaurus sp.? (3 mm tall) One thing I would like to note is that I have since found a paper that helped to clarify the geology of this site which was a point of confusion in my previous trip reports. I made the mistake of referring to this place as the "Fish Bed Conglomerate" when it turns out that title has been used for at least a couple different layers, namely the base of the Austin Chalk and a phosphatic pebble bed that exists a short ways below the base documented by Taff and Leverett way back in 1893. This mixup has caused some confusion it seems in old academia. Anyways the stratigraphic chart (Fig. 2) in the source below shows these two phosphatic layers and some info on them. I kinda had a mind blown moment as I have actually visited both of these layers while looking for the Basal Atco at a couple of locations. The site where these teeth were found along with all my other written Atco adventures did actually in fact occur in the Atco or earliest Coniacian. However, the "second location" noted in the report I've linked below was actually at this Arcadia Park phosphatic pebble bed. These two layers are quite distinct and my "Atco" site definitely better fits the base. The sea levels paper specifically notes the layer as being ripple bedded which I coincidentally took a picture of in my old report! So satisfying when everything clicks into place... Hancock, Jake M., and Ireneusz Walaszczyk. “Mid-Turonian to Coniacian Changes of Sea Level around Dallas, Texas.” Cretaceous Research 25.4 (2004): 459–471. Web. As a bonus for reading through this, here are a couple of nice sharks teeth I found from the same layer. They are my first larger complete Cretalamna from the location and a new species on top of that. They compare best with Cretalamna ewelli which Siversson notes as being present in the Late Coniacian. I have some less impressive Cretalamna from the location that I previously identified as C. gertericorum, but I may have to double check those since it would be weird for two species to show up on top of one another in my opinion. They are very similar-looking species so I wouldn't be surprised if I was mistaken before. Cretalamna ewelli with beautifully splayed cusplets Looking forward to hearing yall's opinions! Thanks

Hey everyone, Just a quick ID post for help in pinning down what exactly these couple of teeth are. Up first is a broken crown to a tooth I found while processing South Bosque material from Central TX for a pet project of mine. It's Turonian in age and looks similar to some small Carchariniformes teeth I've found at the Whiskey Bridge. Note that when I found this tooth, I had not yet visited the Whiskey Bridge, so I am certain this is not a product of cross contamination. Anyways, it's unlike the other specimens I have from the South Bosque and I am struggling to find a genus that matches its shape other than Galeorhinus. Carchariniformes were present in the Mesozoic and Galeorhinus is known all the way back into the Cenomanian, but ones this old are very rare so I am hesitant. I am wondering if any knows another more likely genus for this Turonian tooth? The second tooth is definitely Cretodus, but I am trying to pin down a species. It came from the Atco (Coniacian) which is known to produce Cretodus crassidens, but I have recently learned of another species, Cretodus houghtonorum, that is also in the area and a candidate. Unfortunately, I do not have access to the paper describing C. houghtonorum so it is difficult for me to figure out how to differentiate the two, but just off of secondhand knowledge I believe this one may be C. houghtonorum because of its more gracile non-ovular cusp. The wrinkling on the labial face is very pronounced and travels farther up the cusp than on my C. semiplicatus specimen from the Cenomanian. On the lingual side, the wrinkling is very short whereas they travel much farther on the C. semiplicatus. The root on the suspected C. houghtonorum is extremely pronounced and almost hangs over the cusp and cusplets. Wish I had a C. crassidens to compare to, but the C. semiplicatus is all I've got for now. Luckily they are very similar in mouth position so it's easy to spot differences. Left is tooth in question; Right is C. semiplicatus specimen Tooth in question C. semiplicatus @ThePhysicist @Al Dente @MarcoSr If you know any other shark experts who could help, feel free to ping them in the replies Thanks!

Disclaimer: I'm still not 100% sure if the layer I'm hunting in is the basal Atco, but I am under the impression that it is for now. Hopefully I'll be able to do a hunt at Midlothian with the DPS some time soon to get a reference for what the Atco is really supposed to look like. In the past month, I've taken another visit to my little Atco spot to try and learn the place a bit better. I scouted farther upstream and downstream as well as another creek not so far out. There were some pretty cool finds, but I'll keep the story short since I've already covered this locality in a previous report. After a bit of creek walking, I was relieved to see that the latest storm had washed out some fresh conglomerate for me to start splitting at the main gravel bar. Most of the teeth present in the matrix are extremely weathered from reworking, but now and then, a pristine specimen can be revealed and carefully extracted. The first of these discoveries came from just the second rock I had picked up. Some of you may relate to that moment of disbelief when you open the two slabs and realize you are face to face with a huge tooth in mint condition. I hate having to glue broken teeth together, so I proceeded with extreme caution. Still not totally sure if this is Cretodus houghtonorum or Cretodus crassidens, but for now I am tentatively calling it C. houghtonorum since its cusp is more gracile and seems to lack the ovular shape of C. crassidens. One interesting feature of the tooth is the presence of a an extra little cusplet which can be seen in the labial views between the central cusp and distal cusplet. Whatever species it may be, it is a first in my collection, so I am am pretty content. I traveled a little ways up a feeder creek and came across the root of a decently sized Cretalamna gertericorum. The matrix was hard, so I ended up having to clean it at home. Sadly the central cusp was really banged up. Tough to spot, but the root of C. gertericorum Cretalamna gertericorum. On the left is the new specimen and on the right is one from my first visit to the site after recent repairs. At a later gravel bar, I finally found something sticking out of the matrix that I had been really hoping to find. Some of you may remember that my last trip to this spot had yielded a prearticular tooth to a meter long pycnodont fish called Acrotemnus streckeri. These fish are also documented as having pharyngeal teeth. I managed to finally pocket one at this site and one at the later site I'll soon cover. I can't say for sure these are from A. streckeri, but their large size does make it a candidate. Pycnodont pharyngeal in situ A couple of pharyngeal teeth I will tentatively assign to Acrotemnus streckeri. It's kinda neat these teeth share the bluish grey color of the prearticular tooth. Before I show off the final find from the main Atco site, I'll quickly go over the second location I visited. The plan was to locate the Atco there as well, but with all of the modifications made to the creek, I wasn't able to find the source of the Atco rubble I found scattered along the stream. Nothing remarkable was found, but that isn't too say I didn't come out with at least a dozen small teeth. Here a couple pictures of some interesting geologic formations. Huge ripples were found on a lot of the washed out matrix. Located in the uppermost Arcadia Park was this limy layer that was rich in vertebrate material and gastropods. I came across this giant concretion that really stood out. I wonder if anything's inside it. And here is an overview of the smaller finds from the trips: Top L to R: Squalicorax falcatus, Cretodus houghtonorum, and Cretalamna gertericorum Bot L to R: Xiphactinus sp., Acrotemnus streckeri, and various ptychodus Back to the main site, as I was wrapping up the day, I came across some hardened material on the shale bottom of the creek bed above the conglomerate layer. Usually these sort of things are only broken oyster bits, but the shape and density of this one seemed odd so I went in for a closer look before noticing how dark the object was underneath the algal growths. It soon became clear that this was a string of 5 very large fish vertebrae and I begun working around the fossil to pop it out whole. Thankfully, I was able to do just that and the sight as I flipped it over sent me jumping up and down. I scoured the surrounding area, but did not locate any more of the fish. Makes me imagine one day 90ish million years ago this chunk of fish was all that was left after a shark attack or maybe something of the like. After bringing it home, I was able to scrub off the larger chunks of algae, but a hard "calcareous" layer remained attached directly to the bone. I tried soaking it over multiple nights in a bleach water solution and slowly worked off pieces with a dental pick during the day. The plan was to use the other side as display, so I wasn't too concerned with abusing the algal side, but of course I would have liked to have as little damage done as possible. One of the verts was offset, so it quickly broke off from the stress of picking at it. Later another vert came off, but this wasn't an issue as I could easily glue them back later. The work was tedious and took time. On the display side, I worked off the shale with a needle and frequent brushing. Slowly the form become more and more apparent. Soon enough, I decided it was time to get the paraloid out. On a site with so many professional preppers, I'm sure this doesn't look all that impressive, but I am suuuper happy to have this on display and proud of the work. It's fun to hold and imagine the sheer size of the beast these bones once belonged to. I hope you all enjoy it as well. Thanks for reading

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!

I have been hunting the Basal Atco member of the Austin group in Central Texas for about 7 years. Others say that it is the uppermost part of the Eagle Ford. I don't doubt that it is some type of erosional zone involving the two. I have found hundreds of fossils in it. Most of them are beautiful reddish brown color. Most of them have been damaged somewhat by paleo-erosion before they were left in their final state. Many Basal Atco fossils are very interesting to me, because I can't find them anywhere else. My first area to hunt back in 2015 was a lot of fun. An exposed bluff where a giant chunk of the overhanging bedrock limestone had fallen down into the creek. I'm glad I wasn't under that whenever it fell. But, it left behind a nice exposure of what I came to think represented the Basal Atco. Boy was I wrong. Over 100 Ptychodus and other shark's teeth from the same area within a 1 ft thickness of conglomerate like material. Since then I have been at multiple locations of the same Basal Atco with many different expressions of what that might look like from a soft shaley mudstone to a hard rock-like conglomerate to primarily white thin sandy limestone seams with only occasional fossils in the middle of the bedrock. Most of these Basal Atco exposures have no fossils WHATSOEVER! I have found only half again as many Ptychodus fossils in all the other Basal Atco sites combined. Maybe I'd have better luck hunting the gravel banks - which is not my forte. I found a new location that I was not aware of early this summer. It was kind of fun hunting it because it was different than all the rest. I pulled out a partial ammonite and knew that I was in the Basal Atco formation and that there might be more fossils in there. It was obvious that other people had probably been hunting it some before I had been there. I came a second time and walked the football field length of the seam. If you've ever hunted the Basal Atco, then you know you might find yourself under an overhang of a large bluff that could collapse on you at any moment. This one was not that bad! I have generally avoided the areas with the most extreme overhangs. Those where you feel like you have entered a cave-like area (like Mesa Verde) where the rock acts like a huge roof over your head - that (in my overly cautious mind) could fall at any moment. So my goal was to hopefully find a Ptychodus martini. I have developed long-term inflammation in my wrists and hands. So hammering with a big 3 lb hammer or geologic hammer to break open limestone rock is no longer a pleasant thing. In fact, it can be downright debilitating for the next few days. But I did it this one time and was rewarded with a few Ptychodus teeth out of a 7 ft length x 1ft wide triangular seam of sandy limestone. The largest Ptychodus was 18 mm wide and it initially appeared to be what I was seeking. But, upon further evaluation it was instead a nice Ptychodus latissimus. The latter species is perhaps my favorite from the Atco. Under the light it has a little bit of a rainbow sheen which doesn't come out in the photos. I don't know that it has pyrite as part of the preservation. I've seen and found Ptychodus that were completely pyritized from South Dakota and this was not like them. The first photo is initial shot of the Ptychodus latissimus in the rock. The second is of a similar limestone flaggy rock to the one I found these fossils in. The third is a shot of it in my display area partially still in the rock. The final picture is a shot of one found in North Dakota that is a Ptychodus marginalis that was completely pyritized. Mine is a little smaller. The last photo is a side view of the Ptychodus latissimus. It comes out of the rock but still has the root. You can see how low the crown is. My wife and I have continued our monthly fossil forays (her Christmas gift to me) finding at least one nice Ptychodus fossil on each outing. On the above featured hunt, she and one of my adult daughters were at home with a very unkind version of COVID19. So, my wife kindly invited me to "get some fresh air" and leave the house for a while. So I took her up on it and hunted several places on that hot day. Cheers!

Hello all! I got some fun Post Oak Creek Matrix and am finding all kinds of odd things!! I am not too familiar with the stuff that comes out of POC aside from the shark teeth and crabby stuff (found a couple of nice claws!) so these things have me wondering what they are! Any help is appreciated! 1.First is this little thing: 4 mm 2. Then this weird thing 6 mm (the backside makes me think denticle but the front.....I don't know) 3. Have found quite a few of these - .I think they are some kind of dermal plates? All are aprox 3 mm 4. Another type of dermal plate? 4 mm 5. Perhaps a worn fragment of a vertebra? 4 mm But it is not the same color or texture as any of the other verts I've found in the matrix; 6 An odd bone bit. It has a concave circle on the small end. Perhaps a tail vert? 5 mm 7. Is this perhaps a plesiosar tooth fragment? 4 mm 8. And finally, not sure what tooth this might be. It's curved, but not rounded. It has ridges unlike a shark tooth blade, but is flat like a shark tooth blade. 6mm

Found in Atco formation in Texas, Coniacian age. Looking in my Welton Farish book and I can’t find anything similar. Maybe spines of some sort? Kind of looks like teeth and kind of not. Lost on this one. Scale is in mm.