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Hey everyone! Towards the end of my time down in Austin, I collected a dozen or so bags of matrix across three sites that covered the Bouldin Flags (Cenomanian), South Bosque (Turonian), and basal Atco (Coniacian) of Central Texas. Over the course of the last 6 months, I have processed and tried to identify everything that my sieve caught in order to complete this project of mine. I’m sure there are plenty of errors within this amateur study, but I hope that the overall information it provides will at least be of some use to my fellow hunters who are looking for a centralized place to figure out just what kind of tooth they stumbled upon in their local creek. I know that, especially in my first year of fossil hunting, the seemingly endless list of shark names looked like a mountain too tall to overcome. Perhaps this report might just help to demystify that obstacle. There were many expected finds and some total surprises. I learned a lot myself from this whole endeavor and am excited to share what I found. Special shoutout to @Jackito and @LSCHNELLE for so kindfully sharing their fantastic sites as well as their expertise. This could not have been done without their help! Also, if you have found a species of shark not mentioned in this report from the Bouldin Flags, South Bosque, or Atco of Central Texas, feel free to leave a reply with a photo and some info on your specimen! Enjoy! Abundant (), Common (), Uncommon (), Rare () Bouldin Flags (Cenomanian) The Bouldin Flags represents the end of the Cenomanian stage of the WIS in Central Texas. It carries much of the typical “Woodbinian fauna” that is often associated with Cenomanian sites from across the continent. The formation is “flaggy”, tending to split into layers. Much of the formation can be devoid of vertebrate life, but now and then, extremely rich layers may crop up and yield an extensive diversity of sharks, bony fish, and even reptiles to collect from. Processing the matrix can be difficult. I tried to process only the softest material I could find from productive layers as the harder parts were sometimes almost solid pyrite or totally cemented into an unbreakable stone. Even the parts that are soft tend to carry lots of grit that are rough on the hands and fossils. Nevertheless, the Bouldin Flags has some of the most diverse shark and reptile fauna as well as the richest layers, making it well worth the effort of locating. The majority of the collecting for this formation was done in the Lower Bouldin Flags, however, specimens that also occurred in the limited Upper Bouldin Flags sampling will be marked with an asterisk (*=Upper BF) Lamniformes *Carcharias saskatchewanensis Together with Cenocarcharias tenuiplicatus, these species make up the two most abundant sharks teeth to be found in the Bouldin Flags. They are typically only millimeters in size and tend to separate well from the matrix without breaking. C. saskatchewanensis can be easily differentiated from C. tenuiplicatus by its absence of fine striations on the labial faces of the cusps and cusplets. C. saskatchewanensis and C. tenuiplicatus are distinguished from Haimirichia amonensis by their significantly smaller size. I have also seen this species referred to as Microcarcharias saskatchewanensis. *Cenocarcharias tenuiplicatus A common tiny tooth found in the Bouldin Flags. They are easily identified by the presence of fine striations on the labial faces of their cusps/cusplets. Now and then, they may have an extra pair of cusplets. Cretalamna catoxodon Surprisingly rare given how abundant this genus usually is in other similarly aged strata of Texas. From the entirety of my material, I only came across one identifiable specimen in the final batch. Unlike mature Cretoxyrhina agassizensis, these teeth have a single pair of pointed cusplets and are usually more gracile. Unlike Cretodus semiplicatus, these teeth are more gracile and lack wrinkling on the base of the crown and cusplets. C. catoxodon is a relatively newly defined species within the genus Cretalamna and, to my knowledge, the only one documented from the Cenomanian. Cretodus semiplicatus One of the most coveted shark fossils of the Eagle Ford is the fearsome Cretodus. These are some of the biggest and most robust teeth to be found and can be spotted quickly by their size and diagnostic wrinkled crown bases on both the labial and lingual faces. To my knowledge, C. crassidens does not appear until the Turonian. C. semiplicatus, unlike Cretodus houghtonorum, typically exhibits a U-shaped basal concavity and U-shaped crown base border whereas C. houghtonorum is more of a V-shape in both departments. Both typically have gracile cusps. In my hunting at the Bouldin Flags site, I found one perfect tooth and a single, large broken off cusp to another tooth. Cretomanta canadensis This is one of the most interesting teeth to be had in the Bouldin Flags. Cretomanta has been interpreted as a planktivorous filter feeder. These teeth are sometimes confused with rostral denticles of Ptychotrygon triangularis, however the oral teeth of P. triangularis were not found at all in the Bouldin Flags Site. In contrast, the Atco Site (more on this later) did produce many of these oral teeth. I believe this suggests P. triangularis is likely not the culprit for the pictured specimens. Additionally, Cretomanta canadensis is commonly listed in faunas of other Cenomanian sites. Fairly recently in Northern Mexico, an amazingly preserved ray-like filter-feeding shark was discovered and named Aquilolamna milarcae. Sadly, no teeth were preserved, making it impossible to confirm synonymy between Aquilolamna and Cretomanta, but nevertheless there is a suspected connection between the two which future discoveries may one day prove. *Cretoxyrhina agassizensis On the right are the juvenile C. agassizensis ("Telodontaspis agassizensis") Cretoxyrhina are always a welcome sight and not all that rare for the Bouldin Flags. These are some of the larger teeth to be had and are generally well preserved. They typically do not have cusplets, however some specimens may have poorly developed ones as Cenomanian Cretoxyrhina were still in the process of diminishing them. C. agassizensis is a chronospecies of the genus Cretoxyrhina, representing the time period of the Late Middle Cenomanian to the Early Middle Turonian. Throughout the sifting process, I came across small, thinly cusped and distally curved teeth that somewhat resembled the larger Cretoxyrhina teeth I had as well. In researching possible IDs for these teeth, I came across the species Telodontaspis agassizensis which seemed like a decent match. However, Siversson makes the point that this taxon seems to appear only in places where larger, more typical Cretoxyrhina specimens also occur. It would seem that the two genera are synonymous and these smaller teeth instead belong to juvenile C. agassizensis. *Haimirichia amonensis Medium-sized teeth that are extremely abundant in the Bouldin Flags as well as many other Cenomanian deposits of Texas. A decent degree of heterodonty exists and lateral teeth may have many pairs of cusplets. This species was previously known as Carcharias amonensis, however the discovery of a new and well preserved specimen showed that it possessed enough morphological differences to warrant the creation of the family Haimirichiidae. I originally misidentified these teeth as Scapanorhynchus raphiodon which appears to not exist in the Bouldin Flags. *Squalicorax sp. Squalicorax is one of the most abundant teeth present. They are easily identified by their unique shape that highlights their generalist diet. There is currently much work to be done in properly separating the species of this genus across the Mesozoic, so I will simply refer to all teeth found as Squalicorax sp. Ptychodontiformes *Ptychodus anonymous The most common Ptychodus teeth found in both the Bouldin Flags and South Bosque. P. anonymous can be distinguished from other co-occurring Ptychodus teeth most easily on the basis of having a defined marginal area where the transverse ridges will merge instead of bifurcating and running all the way to the end of the crown. P. anonymous is known to have two distinct morphotypes (Cenomanian vs. Turonian), both of which are represented in this post. The Cenomanian morphotype is common in the Bouldin Flags and are typically smaller and more robust than their Turonian counterparts (however my Turonian specimens are just as small as my Cenomanian ones). Another key difference in the morphotypes is that Turonian teeth have an apparent concentric ornamentation of the marginal area whereas Cenomanian teeth have no such feature. It is possible, in the future, these differences may lead to the creation of a new species between the morphotypes. *Ptychodus decurrens This larger specimen in the lower 3 photos was misidentified. I now believe it to be a P. decurrens from the Upper Bouldin Flags. Ptychodus decurrens is a low crowned tooth that is also numerous in this formation. Like Ptychodus occidentalis, the transverse ridging gradually bifurcates to the edges of the crown as opposed to terminating at a distinct marginal area. These teeth are often broad and have the ability to get quite large in size. The bottom specimen shown was originally misidentified as P. marginalis. I have taken another look and now realize P. decurrens is a stronger ID. Despite it being a fragment, I do not think the tooth shows signs of a concentric orientation of transverse ridges and instead seems to follow the hooked on one side and straight on the other ridge pattern more typical of larger P. decurrens. Also, I initially misidentified the formation the tooth came from as being South Bosque based on visuals alone. After getting the chance to process the matrix for micros, it shares much of the same microfauna with the Lower Bouldin Flags and has little faunal overlap with the South Bosque outcrop. I now believe the location to be Upper Bouldin Flags. Ptychodus occidentalis Ptychodus occidentalis is rarer in the Bouldin Flags than the other Ptychodus. They can be identified by the bifurcating nature of their ridges as they travel through the marginal area of the tooth to the edge of the crown. The crown height tends to be higher than that of Ptychodus decurrens. In comparison to P. anonymous, P. occidentalis generally possesses finer and more numerous transverse ridges. This species is also capable of producing some very large teeth. Ptychodus rhombodus is a smaller-toothed species that commonly occurs in the Cenomanian WIS that also shares bifurcating ridge features. It has been suggested, however, that these may represent a juvenile form of P. occidentalis. Orectolobiformes *Cantioscyllium decipiens Common little teeth that belonged to a Mesozoic nurse shark. The teeth look similar to Chiloscyllium, but have striations present on the labial face. Sclerorhynchiformes *Onchopristis dunklei Although not the rarest to find, Onchopristis dunklei represents an order of sharks that hardly seems to be found in the Bouldin Flags. This species tends to preserve both oral teeth and rostral teeth. The rostral teeth are quite iconic, being best known for the multiple barbs decorating its edge. These teeth are fragile and rarely collected in one piece. From the Lower Bouldin Flags, I collected a handful of oral teeth and broken rostral specimens. In my small sample of Upper Bouldin Flags material, I only collected one O. Dunklei rostral and it happened to be the single complete one in the collection. Hybodontiformes Indet. Hybodontiformes Only a singular specimen of a Hybodontiformes tooth fragment was recovered. I don’t believe enough is present to make a confident determination as to whether it belongs to Meristodonoides or some other genera. It has striations on both sides of the tooth and a slight curvature. Other Fauna Amiid? A single, tiny arrow shaped fish tooth was collected. It is difficult to confidently lay down an identification, but Amiid is a candidate for this morphology. Coniasaurus crassidens Coniasaurus crassidens may be found in the Bouldin Flags on rare occasion. Most commonly, teeth, jaw fragments, and vertebrae are found disarticulated amongst shark teeth and shells. Because of their position within the order Squamata, Coniasaurus vertebrae share many visual similarities with larger mosasaur vertebrae from younger strata such as the Ozan. Although Coniasaurus teeth exhibit heterodonty, most of their teeth have a characteristically bulbous shape that distinguishes them from all co-occurring sharks and fish (though anterior-most maxillary teeth may be quite gracile in contrast). While Coniasaurus seems to be restricted to the Cenomanian in England, American specimens cross the Cenomanian-Turonian oceanic anoxic event (OAE 2) and reach the Middle Turonian with some reports even further beyond. Enchodus sp. Typical of just about every Cretaceous exposure in Texas is the saber-toothed Enchodus. The Bouldin Flags is absolutely filled with them. The teeth are generally quite small and vary in shape. Most commonly, they are flattened and take on a recurved shape. Sometimes they may be conical and completely straight. They may be smooth or have striations. Pachyrhizodus minimus These are very small and resemble miniature mosasaur teeth. They are smooth around their circumference and have a strong distal curvature. Pachyrhizodus is a genus known for having relatively large heads, similar to modern Grouper fish. Protosphyraena sp. Protosphyraena was a genus of fish that heavily resembled modern swordfish. Their teeth are common finds all over Texas. They generally take on a flattened shape and bear two cutting edges. They can sometimes have a slight curvature or stay completely straight. The ones I collected were among the larger fish teeth found. Known but missing sharks Pseudomegachasma comanchensis Despite not having personally collected one, Pseudomegachasma comanchensis is known from the Bouldin Flags. Similar to Cretomanta, these sharks are suspected to have been the oldest elasmobranch planktivorous filter feeders. The lingual protuberances on these teeth are so large, they almost look like backwards root lobes. Ptychodus marginalis Ptychodus marginalis is better known from the South Bosque, but has been previously found in the Bouldin Flags, though it is on the rarer end as far as Ptychodus go. They can get large, sometimes to the size of a golf ball. P. marginalis is distinct from other Texan species of the genera in that its ridges go on to form concentric rings as they travel towards the edges of the crown.