Cotylorhynchus

The genus name Cotylorhynchus comes from the Greek kotyle, cup, hollow, and rhynchos, beak, or snout. The genus was named after the nasal opening, which is surrounded by a depressed, cup-shaped bony surface. The genus Cotylorhynchus contains three species which differ in size and proportion: C. romeri (the type species), C. hancocki, and C. bransoni. There are two size groups in C. romeri, which presumably represents sexual dimorphism. There is no size overlap between adults of C. romeri and C. hancocki, but larger specimens of C. bransoni have roughly the same dimensions as smaller specimens of C. romeri. ==Description==

of C. romeri The skull of Cotylorhynchus exhibits the typical caseid morphology, with a forward sloping snout, very large nasal opening, a skull roof with numerous small depressions, and a very large pineal foramen. The latter is more wide than long, as in Ennatosaurus, and thus differs from that of Euromycter, which is subcircular. The number of teeth in the upper and lower jaws ranges from 16 to 20. In the upper jaw, the anterior teeth are long and slender, while those behind decrease in size posteriorly and are slightly spatulate. All of the marginal teeth have their distal end slightly inclined towards the interior of the mouth, and the top of their crowns each have three small cuspules arranged longitudinally. These teeth also show an enlargement of the central part of the crown. In the lower jaw, the anterior teeth, not denticulate according to Olson, are shorter and tilt slightly forward. Other lower teeth are similar to those in the upper jaw. The postcranial skeleton is massive. The ribs are very long, heavy and curved to form a bulbous body. Ribs are present on all the presacral vertebrae and the first caudal vertebrae. The five posterior presacral ribs are fused with the transverse processes of the vertebrae. The sacrum contains three vertebrae. The neural spines of larger specimens become proportionately taller, especially in the pelvic region. The limbs are short and strong. The femur is characterized by its proximal end having a broad shelf marked by a margin slightly overhanging the dorsal surface of the femur. The pes and manus are broad and short, and terminate in strong, sharp, and curved ungual phalanges which must have supported powerful claws. Muscle and tendon scars are very developed. or in length according to Stovall. Robert Reisz and colleagues have identified several cranial autapomorphies in this species. Cotylorhynchus romeri is distinguished by transversely broad postparietals that contact the supratemporals laterally, a large supratemporal that restricts contact between the parietal and postorbital, a stapes that has a short massive distal shaft and a ventral process that is braced against the quadrate ramus of the pterygoid, both vomers bearing three large teeth along the medial edge of the bone, the presence of teeth on the parasphenoid, and a surangular overlapping the posterodorsal tip of the dentary and excluding it from the coronoid eminence. However, Reisz and colleagues emphasize the fact that these autapomorphies are ambiguous because they are identified, with a few exceptions (a few bones of the palate), on parts of the skull still unknown in other species of the genus, thus limiting comparisons. The relatively short limbs were more robust than those of C. bransoni but less massive than those of C. hancoki. The manus and the pes show a phalangeal formula of 2-2-3-3-2. The species is named after J. Hancock, who made it possible to explore much of the locality of Pease River. Its dimensions also make it one of the largest non-mammalian synapsids. No complete skull of C. hancocki is known. The various known elements (maxilla, dentaries, braincase, palate bones), indicate a skull similar to that of C. romeri but slightly larger. The upper teeth are not fully known. Several isolated mandibles show that the lower dentition had up to 18 slightly spatulate and tricuspid teeth. The cuspules of the upper teeth are weaker than those of the lower teeth. In addition, cuspules of C. hancocki are more pronounced than those of C. romeri, but less developed than those of C. bransoni. Cotylorhynchus bransoni Cotylorhynchus bransoni was named in 1962 by Everett C. Olson and Herbert Barghusen from numerous bones found in the Omega Quarry in Kingfisher County, Oklahoma. Its remains were originally described as coming from the central part of the Flowerpot Formation. The species name honors Dr. Carl C. Branson who, at the time of the species description, was the director of the Oklahoma Geological Survey, and who supported the paleontological research of the Chickasha Formation. The holotype FMNH UR 835, consists of the left side of the pelvis, a left femur, and several partial sacral ribs. Other specimens are represented by FMNH UR 836, a right tibia and fibula, tarsus bones, metatarsals, and phalanges except unguals; FMNH UR 837, a left radius and ulna, and part of the carpal bones; FMNH UR 838, a flattened left astragalus; FMNH UR 839, an immature left tibia; FMNH UR 840, a poorly preserved left fibula from an immature individual; FMNH UR 841, a fragment of the left maxilla with two teeth; FMNH UR 842, two fragments of ungual phalanges; and FMNH UR 843, an ungual phalanx. Further excavations in the Omega quarry have uncovered many additional bones, including several previously unknown skeletal elements. This additional material includes FMNH UR 905, a partial foot; FMNH UR 910, cervical ribs; FMNH UR 912, a clavicle; FMNH UR 913, a chevron; FMNH UR 915, a series of vertebrae; FMNH UR 918 and 919, two scapulo-coracoids; FMNH UR 923, sacral vertebrae; FMNH UR 929, a pterygoid; and FMNH UR 937, caudal vertebrae. Finally, three sites in the Hitchcock area of Blaine County provided specimens UR 972, caudal vertebrae; UR 982, 4 dorsal vertebrae; UR 983, dorsal vertebrae; UR 984, an incomplete humerus; and UR 988, part of the pelvis and a complete articulated foot still associated with part of the tibia and fibula. C. bransoni is the smallest known species of the genus Cotylorhynchus, with its largest representatives comparable in size to the smallest individuals of C. romeri. The skull is poorly known and is only represented by two dentigerous bones: a fragment of a maxilla and a pterygoid. The teeth present on these elements distinguish C. bransoni from the other two species of the genus. The two tricuspid teeth preserved on the maxilla show more developed cuspules than those observed in C. romeri and C. hancocki. The pterygoid has fewer, larger and more robust teeth than those present in the pterygoid of C. romeri. The scapulocoracoid has a proportionally narrower scapular blade than in the other two species. The glenoid cavity is somewhat longer in proportion to its width than in the other two species, and the anterior part of the coracoid plate is less extended anteriorly. The radius and ulna are relatively thin and short. The pelvis is characterized by the strong development of the ilium, which rises like a lamina above the acetabulum. The femur is gracile with a slender shaft and a fourth trochanter lying far down the shaft. The distal condyles are widely spaced. The astragalus is characterized by the presence of a very large foramen, a feature not present in the other two species. Olson and Barghusen thought that the phalangeal formula of the foot in C. bransoni was 2-2-2-3-2, a smaller formula than that of the two other species of Cotylorhynchus. However, Romano and Nicosia showed in 2015 that digit III had three phalanges and not two. Thus, the phalangeal formula of the foot of C. bransoni was 2-2-3-3-2 as in C. romeri and probably also in C. hancocki. ==Phylogeny==

All phylogenetics studies of caseids consider Cotylorhynchus to be a taxon close to the genera Ennatosaurus and Angelosaurus. In the first phylogenetic analysis of caseids published in 2008, the species Cotylorhynchus romeri is recovered as the sister group of Angelosaurus dolani. Below is the first caseid cladogram published by Maddin et al. in 2008. Below is the caseasaurs cladogram released by Benson in 2012. Below are the two caseids cladograms published by Berman and colleagues in 2020. }} }} A phylogenetic analysis published in 2022 by Werneburg and colleagues suggests that the genus Cotylorhynchus would be paraphyletic. According to these authors, the species Cotylorhynchus hancocki and C. bransoni would not belong to this genus and would require a detailed revision to clarify their status, these taxa not having been studied since the 1960s. In this analysis, the type species C. romeri is positioned just above the genus Angelosaurus, and forms a polytomy with a clade containing Ruthenosaurus and Caseopsis and another clade containing Alierasaurus, the other two species of Cotylorhynchus, and Lalieudorhynchus. Within the latter clade, Alierasaurus is the sister group of "Cotylorhynchus" bransoni and a more derived clade including Lalieudorhynchus and "Cotylorhynchus" hancocki. Below is the cladogram published by Werneburg and colleagues in 2022. }} == Paleobiology ==

Diet The highly developed, barrel-shaped rib cage indicates the presence of a massive digestive system suitable for ingesting large amounts of low-nutrient plants. The dentition of Cotylorhynchus also shows that it was clearly herbivorous. The front teeth, longer and slightly curved, probably served to gather vegetation in the mouth. The tricuspid marginal teeth were well suited for slicing and cutting vegetation. The hyoid apparatus preserved in some caseids (Euromycter and Ennatosaurus), indicates the existence of a relatively mobile massive tongue which must have worked in concert with the palatal teeth during swallowing. The tongue had to press the plant pieces against the palate in order to puncture the food with the large palatal teeth, an action which may have served to enhance the cellulolytic fermentation of food in the intestine. Another hypothesis suggests that the caseids could have used their powerful forelimbs to fold large plants towards them, which they would have torn off with their powerful claws. According to Reisz and colleagues the presence of numerous skeletons of the amphibian Brachydectes preserved in estivation and of the lungfish Gnathorhiza, another well-known aestivator, combined with the absence of obligate aquatic vertebrates strongly suggests that the Hennessey fauna lived in a dry habitat periodically punctuated by monsoons. Combined with the fact that Cotylorhynchus shows no morphological adaptations to an aquatic lifestyle, these authors consider it as a terrestrial animal that had to endure monsoon rains, with some individuals occasionally succumbing to major floods. In 2022, Werneburg and colleagues proposed a somewhat different semiaquatic lifestyle, in which large caseids like Lalieudorhynchus (whose bone texture is even more osteoporotic than that of Cotylorhynchus) would be ecological equivalents of modern hippos, passing part of their time in the water (being underwater walkers rather than swimming animals) but coming on land for food. == Stratigraphic distribution ==

foramen) and ventral views. No radiometric dating is available for the geological formations containing Cotylorhynchus fossils. The oldest species is C. romeri from the Hennessey Formation in Oklahoma. This formation is considered contemporary with the upper part of the Clear Fork Group (Choza Formation) of Texas. Ammonoid faunas found in marine strata present at the base and top of the Clear Fork Group indicate that the three formations that compose it (Arroyo, Vale, and Choza) are entirely included in the Kungurian. The other two species of Cotylorhynchus are younger and come from the San Angelo and Chickasha formations. The estimation of the geological age of these two formations has been the subject of many interpretations, these alternatively assigning them a late Cisuralian (Kungurian) and/or basal Guadalupian (Roadian) age. In Texas, the species Cotylorhynchus hancocki comes from the San Angelo Formation. This formation overlies the Clear Fork Group and is overlain by the Blaine Formation. According to Spencer G. Lucas and colleagues, fusulins found in a marine intercalation of the San Angelo Formation, as well as ammonoids present at the base of the overlying Blaine Formation, indicated a Kungurian age. Moreover, according to these authors, the base of the San Andres Formation, located further west and considered a lateral equivalent of the Blaine Formation, is in the Neostreptognathodus prayi conodont zone, the second of the three Kungurian conodont biozones. The base of the Blaine Formation would therefore belong to this Kungurian biozone, suggesting that the underlying San Angelo Formation and C. hancocki would be slightly older than the N. prayi conodont zone with a lower Kungurian age. However, Sigi Maho and colleagues have pointed out that several genera of Permian tetrapods had a wide temporal distribution, such as Dimetrodon and Diplocaulus, and that the presence of the genus Macroleter in both Russia and Oklahoma (represented by two different species) is not an evidence of a middle Permian age for the Chickasha Formation. The same authors also point to the example of the varanopid Mesenosaurus, which is present both in the Middle Permian of European Russia and by a separate species in Oklahoma, in a locality radiometrically dated to the early Permian (Artinskian). Cisuralian occurrences of P. ollieri come from the Hermit (Arizona), Rabéjac (France) and Peranera (Spain) formations, all of Artinskian age, and also from the San Angelo Formation. Thus, in the current state of knowledge, the age of the Chickasha Formation can hardly be assessed from its fauna. However, the stratigraphic position of the Chickasha Formation compared to that of the San Angelo Formation, and its probable early Roadian age inferred by magnetostratigraphy, indicate that the Chickasha fauna represents the most recent Permian faunal assemblage of North America. == Paleoenvironments ==

In the Permian, most of the landmasses were united in a single supercontinent, Pangea. It was then roughly C-shaped: its northern (Laurasia) and southern (Gondwana) parts were connected to the west but separated to the east by the Tethys Ocean. A long string of microcontinents, grouped under the name of Cimmeria, divided the Tethys in two : the Paleo-Tethys in the north, and the Neo-Tethys in the south. The Hennessey, San Angelo, and Chickasha formations correspond mainly to fluvial and aeolian sediments deposited in a vast deltaic plain dotted with lakes and lagoons. This coastal plain was bordered to the west by a sea that occupied what is today the Gulf of Mexico and the southernmost part of North America. The rivers ending in the delta came from modest reliefs located further east and corresponding to the ancestral uplifts of the Ouachita, Arbuckle and Wichita mountains. The climate was subtropical with moderate and seasonal rains. There was a summer monsoon as well as a dry winter season. The monsoon was relatively weak, due to the limited size of the sea and the small differential between summer and winter temperatures. The presence of evaporites indicates significant aridity interrupted by seasonal flooding. and Rhodotheratus parvus, the lungfish Gnathorhiza, Rhynchonkos, Aletrimyti, and Dvellacanus. Gnathorhiza and Brachydectes were able to aestivate in burrows during prolonged periods of aridity. Amphisauropus tracks from the Hennessey Formation have however been reclassified in the ichnogenus Hyloidichnus, which corresponds to footprints of captorhinid eureptiles. San Angelo Formation The San Angelo Formation is composed at its base of unfossiliferous hard, green, gray and brown sandstones and fine conglomerates. The central part of the formation consists mainly of red mudstones corresponding to clayey and silty mud deposited in coastal plains during periodic flooding episodes. These red mudstones are interspersed with a thin level of green sandstone, sandy shales, and evaporites. These correspond to a minor and ephemeral encroachment of estuaries, lagoons, and very shallow seas on the terrestrial part of the delta. The caseids Angelosaurus dolani and Caseoides sanangeloensis are present in the red mudstones of this part of the formation. The upper part of the San Angelo Formation is characterized by the preponderance of coarse sediments such as sandstones and conglomerates, but also including at its base sandy mudstones and at its top pure red mudstones. According to Olson, these sediments were deposited by wider and more powerful rivers than those of the central part of the formation. However, in Oklahoma, strata equivalent to the San Angelo Formation, which were also considered fluvio-deltaic and coastal deposits, have been reinterpreted as being of aeolian origin. This level is characterized by the absence of the genus Angelosaurus and by the abundance of Cotylorhynchus hanckoki. The latter is most often represented by a single individual in each locality, with the exception of the Kahn quarry. This site has yielded many specimens distributed in several stratigraphic levels. The richest level, consisting of green, sometimes brown, sandy mudstones has provided the remains of at least 15 individuals. Several are partially articulated while others are represented by isolated bones. After being transported to the site, some bones remained exposed on the surface for some time, as indicated by the presence, on some of them, of a thin silt layer very different from the rest of the matrix. Several bones indicate that some carcasses were partially devoured. The taphonomy of the site therefore indicates that the corpses of C. hancocki were transported during a flooding episode, deposited as the waters receded, subjected to the action of predators and scavengers, and then buried later may be during a new flood. A process that would have been repeated several times. Large masses of vegetation have also been transported and have been found in direct association with vertebrates. Chickasha Formation The Chickasha Formation corresponds to the central part of the Flowerpot Formation in which it is locally inserted. The sediments that compose it are varied and include red shales, sandstones, mudstones, conglomerates, and evaporites, deposited in floodplains and channels bordering the sea and coastal lagoons. In the Omega quarry, all the fossils come from sandstones, mudstones and hard, siliceous conglomerates, arranged in lenses. They correspond to channel deposits where the skeletons of Cotylorhynchus bransoni have accumulated, but also those of a second caseid, Angelosaurus romeri, and those of the captorhinid Rothianiscus robustus. the nycteroleterid Macroleter and the varanopids Varanodon and Watongia . == Notes ==