''Cotylorhynchus'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of herbivorous caseid

synapsid Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant rept ...

s that lived during the late Lower Permian ( Kungurian) and possibly the early

Middle Permian The Guadalupian is the second and middle series/epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± 0. ...

( Roadian) in what is now

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

and

Oklahoma Oklahoma ( ; Choctaw language, Choctaw: , ) is a landlocked U.S. state, state in the South Central United States, South Central region of the United States. It borders Texas to the south and west, Kansas to the north, Missouri to the northea ...

. The large number of specimens found make it the best-known caseid. Like all large herbivorous caseids, ''Cotylorhynchus'' had a short snout sloping forward and very large external nares. The head was very small compared to the size of the body. The latter was massive, barrel-shaped, and ended with a long tail. The limbs were short and robust. The hands and feet had short, broad fingers with powerful claws. The barrel-shaped body must have housed large intestines, suggesting that the animal had to feed on a large quantity of plants of low nutritional value. Caseids are generally considered to be terrestrial, though a semi-aquatic lifestyle has been proposed by some authors. The genus ''Cotylorhynchus'' is represented by three species, the largest of which could reach more than 6 m in length. However, a study published in 2022 suggests that the genus may be

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

, with two of the three species possibly belonging to separate genera.

Discovery

The genus name ''Cotylorhynchus'' comes from the Greek ''kotyle'', cup, hollow, and ''rhynchos'', beak, or snout. The genus was named so because of 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''. In ''C. romeri'' there are two size groups which presumably represent

sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

. 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''. In 2022, Werneburg and colleagues suggested that the species ''C. hancocki'' and ''C. bransoni'' might not belong to the genus ''Cotylorhynchus''. These authors consider that a detailed revision of these two taxa is necessary to clarify their status.

Description

The

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

of ''Cotylorhynchus'' shows the typical caseid morphology with a forward sloping

snout A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, Rostrum (anatomy), rostrum, beak or proboscis. The wet furless surface around the nostrils of the n ...

, very large nasal opening, a skull roof with numerous small depressions, and a very large pineal

foramen In anatomy and osteology, a foramen (; : foramina, or foramens ; ) is an opening or enclosed gap within the dense connective tissue (bones and deep fasciae) of extant and extinct amniote animals, typically to allow passage of nerves, artery, ...

. The latter is wider than long as in '' Ennatosaurus'' and thus differs from that of '' Euromycter'' which is subcircular. The number of

teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

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 the marginal teeth have their distal end slightly inclined towards the interior of the mouth and the top of their crown each have three small cuspules arranged longitudinally. These teeth also show an enlargement of the central part of the

crown A crown is a traditional form of head adornment, or hat, worn by monarchs as a symbol of their power and dignity. A crown is often, by extension, a symbol of the monarch's government or items endorsed by it. The word itself is used, parti ...

. 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

rib In vertebrate anatomy, ribs () are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the ...

s are very long, heavy and curved to form a bulbous body. Ribs are present on all the pre-sacral

vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...

e and the first caudal vertebrae. The five posterior presacral ribs are fused with the transverse processes of the vertebrae. The

sacrum The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...

contains three vertebrae. The

neural spines Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

of larger specimens become proportionately taller, especially in the

pelvic The pelvis (: pelves or pelvises) is the lower part of an anatomical trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis or pelvic skeleton). ...

region. The limbs are short and strong. The

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

is characterized by its

proximal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

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 An ungual (from Latin ''unguis'', i.e. ''nail'') is a highly modified distal toe bone which ends in a hoof, claw, or nail. Elephants and ungulates have ungual phalanges, as did the sauropod Sauropoda (), whose members are known as sauropods (; ...

phalanges The phalanges (: phalanx ) are digit (anatomy), digital bones in the hands and foot, feet of most vertebrates. In primates, the Thumb, thumbs and Hallux, big toes have two phalanges while the other Digit (anatomy), digits have three phalanges. ...

which must have supported powerful

claw A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or Arthro ...

Muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

and

tendon A tendon or sinew is a tough band of fibrous connective tissue, dense fibrous connective tissue that connects skeletal muscle, muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tensi ...

scars are very developed.

''Cotylorhynchus romeri''

The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

''Cotylorhynchus romeri'' is the best known species of the genus. It was erected in 1937 by J. Willis Stovall from the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

OMNH 00637, consisting of the right side of a skull, an incomplete interclavicle, and the right and left manus, found in the red

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

s of the lower part of the Hennessey Formation, near the locality of Navina,

Logan County Logan County is the name of ten current counties and one former county in the United States: * Logan County, Arkansas * Logan County, Colorado * Logan County, Idaho (1889–1895) * Logan County, Illinois * Logan County, Kansas * Logan County ...

. The name of the species honors the American paleontologist Alfred Sherwood Romer. Shortly after the holotype's discovery, numerous specimens were found in some 20 sites surrounding the town of Norman, Cleveland County, also from the Hennessey Formation. Several fairly complete skeletons and many more fragmentary ones, totalize about 40 individuals. Specimens from the two regions are more or less contemporaneous and are only known within a thick

stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...

interval. In Navina, the holotype comes from a level about above the base of the Hennessey Formation. The numerous specimens from the Norman area have been found in several layers located between above the base of the formation. The holotype of ''C. romeri'' has 20 teeth in upper jaws (3 on the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...

and 17 on the

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

) and 19 teeth in lower jaws. ''C. romeri'' from the Norman region show a lower number of teeth. Four skulls where tooth counting was possible have 15 or 16 teeth in upper jaws. Some authors have thus considered that the holotype of ''C. romeri'' and the referred specimens from Norman represent two different species. However, the lack of specimens in the type locality (the holotype of ''C. romeri'' being the only known fossil there) and the number of teeth being the only difference with the ''Cotylorhynchus'' from Norman, it was decided to keep all these specimens in the same species. ''C. romeri'' is a large species that can exceed in length and in weigh according to Romer and Price, or in length according to Stoval. Robert Reisz and colleagues have identified several cranial autapomorphies in this species. ''Cotylorhynchus romeri'' is distinguished by transversely broad

postparietal Postparietals are cranial bones present in fish and many Tetrapod, tetrapods. Although initially a pair of bones, many lineages possess postparietals which were fused into a single bone. The postparietals were Dermal bone, dermal bones situated alo ...

s that contact the supratemporals laterally, a large supratemporal that restricts contact between the parietal and

postorbital The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ve ...

, a

stapes The ''stapes'' or stirrup is a bone in the middle ear of humans and other tetrapods which is involved in the conduction of sound vibrations to the inner ear. This bone is connected to the oval window by its annular ligament, which allows the f ...

that has a short massive distal shaft and a ventral

process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management * Business process, activities that produce a specific s ...

that is braced against the quadrate ramus of the pterygoid, both

vomer The vomer (; ) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones. The vomer forms ...

s bearing three large teeth along the medial edge of the bone, the presence of teeth on the parasphenoid, and a

surangular The surangular or suprangular is a jaw bone found in most land vertebrates, except mammals. Usually in the back of the jaw, on the upper edge, it is connected to all other jaw bones: dentary, angular bone, angular, splenial and articular. It is o ...

overlapping the posterodorsal tip of the

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

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 The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sep ...

), on parts of the skull still unknown in other species of the genus, thus limiting comparisons. As the other two species of ''Cotylorhynchus'', the dentition consists of tricuspid teeth (except for the most anterior teeth). However, ''C. romeri'' is the species where the cuspules are least developed. According to Olson, the premaxillary teeth had no cuspules. The latter, however, have been reported on the premaxillary teeth by Reisz and colleagues. All marginal teeth have their distal ends curved lingually. Numerous teeth are also present on several bones of the palate. A short row of three large, slightly recurved teeth are present on each vomer. They are taller than all other teeth on the palate. The palatines bear 10 subconical teeth located on a slightly thickened region of bone adjacent to the middle part of the suture shared with the pterygoid. The latter, triangular in shape, has many teeth divided into four distinct groups: a medial row bordering the interpterygoid vacuity, a group of smaller teeth which contributes to the pterygo-palatine tooth cluster, a posterolateral cluster of very small teeth on the transverse flange of the pterygoid, and behind this cluster a row of large teeth that borders the posterior margin of the transverse flange and extends medially to the basicranial region. In summary, the pterygoid bears more, smaller and slender teeth than those present on the pterygoid of ''C. bransoni''. A few teeth are also present on the parasphenoid. Several palatal teeth have well-preserved tips showing the same distal morphology as marginal teeth with three small cuspules. In lower jaws, the dentary has between 16 and 19 teeth, which have the same morphology as the teeth of the upper jaws. In ''C. romeri'', the dental row does not show spaces for replacement teeth which could be related to reduced rates of tooth replacement and increased longevity of functional teeth. The

vertebral column The spinal column, also known as the vertebral column, spine or backbone, is the core part of the axial skeleton in vertebrates. The vertebral column is the defining and eponymous characteristic of the vertebrate. The spinal column is a segmente ...

consists of 25 or 26 presacral vertebrae, 3 sacral vertebrae, and approximately 55 caudal vertebrae. ''C. romeri'' is distinguished by its widely spaced postzygapophyses on the dorsal vertebrae, while in ''C. hancocki'' and ''C. bransoni'' they usually contact along the midline. 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 skeletons from the Norman region show two different size groups within adult specimens. One of these groups is composed of individuals about 20% smaller than those in the other group. This size difference was interpreted as possible specific differentiation or more likely as the expression of

''Cotylorhynchus hancocki''

''Cotylorhynchus hancocki'' was named in 1953 by Everett Claire Olson and James R. Beerbower, from a right

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

and a proximal end of a

tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

(constituting the holotype FMNH UR 154) found in the upper part of the San Angelo Formation, near the Pease River, in Hardeman County,

. The species is named after J. Hancock, who made it possible to explore much of the locality of Pease River. Subsequently, more than sixty specimens, ranging from isolated bone to nearly complete skeleton, were discovered in several localities in Knox County, the majority however coming from the Kahn quarry. This site has yielded the most complete specimens of the species such as FMNH UR 581, an almost complete skeleton missing only the skull, some cervical vertebrae, a scapulocoracoid and some limb bones; FMNH UR 622, a partial skeleton including part of the skull and

, various vertebrae, ribs, limb bones,

clavicle The clavicle, collarbone, or keybone is a slender, S-shaped long bone approximately long that serves as a strut between the scapula, shoulder blade and the sternum (breastbone). There are two clavicles, one on each side of the body. The clavic ...

, and bones of the foot; and FMNH UR 703, part of the skeleton of a very large individual including dorsal, lumbar, sacral, and caudal vertebrae, pelvis, femur,

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

, and ribs. Other notable specimens include several isolated cranial bones. All of the skull bones known in this species come from the Kahn quarry. With a size of up to in length and a weight of over , ''C. hancocki'' is by far the largest species of the genus, and is one of the largest known caseids along with the genus '' Alierasaurus''. Its dimensions also make it one of the largest non-

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

ian

s. 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''. The postcranial skeleton is distinguished by the morphology and proportions of limbs, vertebrae, and pelvis. The scapulocoracoid is characterized by the presence of a supraglenoid

on the

scapula The scapula (: scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either side ...

r blade. Such a foramen is absent in the other two species of ''Cotylorhynchus'' and in caseids in general but is present in the genus '' Lalieudorhynchus''. The scapula has a process-like bulged anteromedial margin as in ''Lalieudorhynchus''. The humerus has a flat, very broad and thin

epicondyle An epicondyle () is a rounded eminence on a bone that lies upon a condyle ('' epi-'', "upon" + ''condyle'', from a root meaning "knuckle" or "rounded articular area"). There are various epicondyles in the human skeleton The human skeleton is ...

, and a completely closed

entepicondylar foramen The entepicondylar foramen is an opening in the distal (far) end of the humerus (upper arm bone) present in some mammals. It is often present in primitive placentals, such as the enigmatic Madagascan '' Plesiorycteropus''. In most Neotominae and a ...

. The most complete vertebral column is that of specimen FMNH UR 581 in which there are seventeen presacral vertebrae and thirty-nine caudal vertebrae in articulation. A characteristic related to the very large size of this species is the presence of a prominent '' hyposphene'' on the postzygapophyses of the dorsal vertebrae, a character shared with ''Lalieudorhynchus''. This supplementary intervertebral joint strengthened and stabilized the vertebral column to support the weight of the animal. The neural spine of the first caudal and sacral vertebra is very elongated dorsally as in ''Lalieudorhynchus''. The limb bones are very strong. The femur in particular is very massive with a relatively short shaft and a very developed internal trochanter, another character shared with ''Lalieudorhynchus''. The bone as a whole is proportionately shorter and wider than that of the other two species of ''Cotylorhynchus''. The pelvis is characterized by a distinctly larger anterolateral projection of the pubis than in ''C. romeri'', and a sacrum with a very large anterior sacral rib, while the second and third sacral ribs are small and less specialized. An incomplete foot is preserved in FMNH UR 581. The

astragalus Astragalus may refer to: * ''Astragalus'' (plant), a large genus of herbs and small shrubs *Astragalus (bone) The talus (; Latin for ankle or ankle bone; : tali), talus bone, astragalus (), or ankle bone is one of the group of foot bones known ...

of ''C. hancocki'' differs from that of the other two species of ''Cotylorhynchus'' and resembles that of ''Lalieudorhynchus'' in being nearly as broad as long. The digit IV is complete and has three elements. The positions of the preserved elements of the digits II and III suggest a phalangeal formula of ? -2-2-3-?.

''Cotylorhynchus bransoni''

''Cotylorhynchus bransoni'' was named in 1962 by Everett C. Olson and Herbert Barghusen from numerous bones found in the

Omega Omega (, ; uppercase Ω, lowercase ω; Ancient Greek ὦ, later ὦ μέγα, Modern Greek ωμέγα) is the twenty-fourth and last letter in the Greek alphabet. In the Greek numerals, Greek numeric system/isopsephy (gematria), it has a value ...

Quarry in Kingfisher County,

. Its remains were originally described as coming from the central part of the Flowerpot Formation. Olson later corrected this attribution by specifying that these remains belong to a tongue of the Chickasha Formation ( El Reno

Group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...

) whose deposits interfinger in places with those of the Flowerpot, Blaine, and Dog Creek formations. 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 The fibula (: fibulae or fibulas) or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. ...

, tarsus bones, metatarsals, and phalanges except unguals; FMNH UR 837, a left radius and ulna, and part of the

carpal bones The carpal bones are the eight small bones that make up the wrist (carpus) that connects the hand to the forearm. The terms "carpus" and "carpal" are derived from the Latin wikt:carpus#Latin, carpus and the Greek language, Greek wikt:καρπός ...

; FMNH UR 838, a flattened left

; 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

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 The glenoid fossa of the scapula or the glenoid cavity is a bone part of the shoulder. The word ''glenoid'' is pronounced or (both are common) and is from , "socket", reflecting the shoulder joint's ball-and-socket form. It is a shallow, pyri ...

is somewhat longer in proportion to its width than in the other two species, and the anterior part of the

coracoid A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is n ...

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 acetabulum (; : acetabula), also called the cotyloid cavity, is a wikt:concave, concave surface of the pelvis. The femur head, head of the femur meets with the pelvis at the acetabulum, forming the Hip#Articulation, hip joint. Structure The ...

. The femur is gracile with a slender shaft and a fourth trochanter lying far down the shaft. The

distal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provi ...

condyle A condyle (;Entry "condyle"
in

s are widely spaced. The astragalus is characterized by the presence of a very large

, 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 In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

studies of caseids consider ''Cotylorhynchus'' to be a

taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

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 In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

of ''Angelosaurus dolani''. Below is the first caseid cladogram published by Maddin et al. in 2008. Another phylogenetic analysis performed in 2012 by Benson identifies ''Cotylorhynchus romeri'' as the sister group of the two species ''C. Hancocki'' and ''C. bransoni''. Below is the caseasaurs cladogram released by Benson in 2012. In 2015, Romano and Nicosia published the first

cladistic Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...

study including almost all caseids, except the very fragmentary taxa such as '' Alierasaurus ronchii'' and '' Angelosaurus greeni''. In this analysis, the three species of ''Cotylorhynchus'' form a clade with the genus '' Ruthenosaurus'', and this clade is the sister group of a clade containing the genera ''Angelosaurus'' and ''Ennatosaurus''. Below is the caseid cladogram published by Romano and Nicosia in 2015. In 2020, two

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

s published by Berman and colleagues also recover ''Cotylorhynchus'' as one of the most derived caseids. In the first cladogram, the three species of ''Cotylorhynchus'' together with ''Angelosaurus'' and ''Alierasaurus'' form an unresolved polytomy. In the second cladogram, ''Cotylorhynchus hancocki'' and ''C. bransoni'' are sister taxa and form a polytomy with ''Cotylorhynchus romeri'' and ''Alierasaurus''. 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 The rib cage or thoracic cage is an endoskeletal enclosure in the thorax of most vertebrates that comprises the ribs, vertebral column and sternum, which protect the vital organs of the thoracic cavity, such as the heart, lungs and great ve ...

indicates the presence of a massive

digestive system The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller compone ...

suitable for ingesting large amounts of low-nutrient

plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...

s. 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 The tongue is a Muscle, muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for chewing and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper s ...

which must have worked in concert with the palatal teeth during

swallowing Swallowing, also called deglutition or inglutition in scientific and medical contexts, is a physical process of an animal's digestive tract (e.g. that of a human body) that allows for an ingested substance (typically food) to pass from the mou ...

. 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. The low number of cuspules (three) on the teeth of ''Cotylorhynchus'' indicates that this genus was adapted to a different fodder (or range of fodder) than other herbivorous caseids having a greater number of cuspules ('' Angelosaurus'', '' Euromycter'' and '' Ennatosaurus'' having respectively 5, 5 to 8, and 5 to 7 cuspules).

Terrestrial vs semiaquatic lifestyle

''Cotylorhynchus'' and caseids in general are usually considered primarily terrestrial animals. Everett C. Olson in particular considered that the degree of ossification of the skeleton, the relatively short feet and hands, the massive claws, the limbs with very powerful extensor muscles, and the strong sacrum, strongly suggested a terrestrial lifestyle. Olson did not rule out that caseids spent some time in water, but he considered locomotion on land to be an important aspect of their lifestyle. It has been suggested that the very powerful forelimbs, with strong and very tendinous extensor muscles, as well as very massive claws, could be used to dig up roots or tubers. However, the very short

neck The neck is the part of the body in many vertebrates that connects the head to the torso. It supports the weight of the head and protects the nerves that transmit sensory and motor information between the brain and the rest of the body. Addition ...

implied a low amplitude of vertical movements of the head which precluded the large species from feeding at ground level. 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. Other hypotheses suggest that some caseids such as ''Cotylorhynchus'' used their limbs with powerful claws to defend themselves against predators, or during intraspecific activities linked in particular to

reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. There are two forms of reproduction: Asexual reproduction, asexual and Sexual ...

. According to Olson, an interesting thing about this, is that almost all known specimens of the species ''Cotylorhynchus hancocki'' have one to ten ribs broken and healed during life. Finally, for some authors, the large derived caseids would have been

semiaquatic In biology, being semi-aquatic refers to various macroorganisms that live regularly in both aquatic and terrestrial environments. When referring to animals, the term describes those that actively spend part of their daily time in water (in ...

animals that used their hands with large claws like

paddle A paddle is a handheld tool with an elongated handle and a flat, widened end (the ''blade'') used as a lever to apply force onto the bladed end. It most commonly describes a completely handheld tool used to propel a human-powered watercraft by p ...

s, which could also be used to manipulate the plants on which they fed. Cotylorhynchus romeri resting

Indeed, in 2016, Lambertz and colleagues questioned the terrestrial lifestyle of large caseids such as ''Cotylorhynchus''. These authors showed that the bone microstructure of the humerus, femur, and ribs of adult and immature ''Cotylorhynchus'' specimens resembled that of aquatic animals rather than terrestrial animals, with a very spongy bone structure, with an extremely thin

cortex Cortex or cortical may refer to: Biology * Cortex (anatomy), the outermost layer of an organ ** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain'' *** Motor cortex, the regions of the cerebral cortex i ...

, and the absence of distinct medullary cavities. This low bone density would have been a handicap for animals weighing several hundred kilograms, and with a strictly terrestrial lifestyle. Lambertz et al. also found that the joints between the vertebrae and the dorsal ribs only allowed small ranges of motion of the rib cage, thus limiting rib ventilation. To overcome this, they proposed that a proto- diaphragm was present to facilitate breathing, especially in aquatic environment. These authors also argued that the arid paleoclimates to which the caseid localities correspond are not incompatible with a semiaquatic lifestyle of these animals. These paleoenvironments included a significant number of aquatic habitats (rivers, lakes and lagoons). The arid conditions could have been the reason that the animals would sometimes have gathered and eventually died. In addition, arid environments have a low density of plants, which would require even more locomotor effort to find foods. For Lambertz et al., large caseids such as ''Cotylorhynchus'' were mainly aquatic animals that only came on dry land for the purposes of reproduction or

thermoregulation Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...

. This hypothesis is however disputed by Kenneth Angielczyk and Christian Kammerer as well as by Robert Reisz and colleagues based on

paleontological Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

and taphonomic data combined with the absence in these large caseids of morphological adaptations to an aquatic lifestyle. According to Angielczyk and Kammerer, the low bone density of caseids identified by Lambertz et al. does not resemble that of semiaquatic animals, which tend to have a more strongly ossified skeleton to provide passive

buoyancy Buoyancy (), or upthrust, is the force exerted by a fluid opposing the weight of a partially or fully immersed object (which may be also be a parcel of fluid). In a column of fluid, pressure increases with depth as a result of the weight of t ...

control and increased stability against current and wave action. ''Cotylorhynchus'' bone microstructure is more similar to what is seen in animals living in the open ocean, such as

cetacea Cetacea (; , ) is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively c ...

ns and

pinniped Pinnipeds (pronounced ), commonly known as seals, are a widely range (biology), distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant taxon, extant families Odobenidae (whose onl ...

s, which emphasize high maneuverability, rapid acceleration and hydrodynamic control of buoyancy. However, the caseid morphology was totally incompatible with a

pelagic The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...

lifestyle. Thus, due to these unusual data, Angielczyk and Kammerer consider that the available evidence is still insufficient to question the more widely assumed terrestrial lifestyle of caseids. 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 A hippo or hippopotamus is either of two species of large African mammal which live mainly in and near water: * Hippopotamus * Pygmy hippopotamus Hippo or Hippos may also refer to: Toponymy * The ancient city of Hippo Regius (modern Annaba, Alg ...

, passing part of their time in the water (being underwater walkers rather than swimming animals) but coming on land for food.

Stratigraphic distribution

radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to Chronological dating, date materials such as Rock (geology), rocks or carbon, in which trace radioactive impurity, impurities were selectively incorporat ...

is available for the

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

s 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 In geology and related fields, a stratum (: strata) is a layer of Rock (geology), rock or sediment characterized by certain Lithology, lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by v ...

present at the base and top of the Clear Fork Group indicate that the three formations that compose it ( Arroyo,

Vale A vale is a type of valley. Vale may also refer to: Places Georgia * Vale, Georgia, a town in the Samtskhe-Javakheti region Norway * Våle, a historic municipality Portugal * Vale (Santa Maria da Feira), a former civil parish in the municip ...

, 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 The Cisuralian, also known as the Early Permian, is the first series/epoch of the Permian. The Cisuralian was preceded by the Pennsylvanian and followed by the Guadalupian. The Cisuralian Epoch is named after the western slopes of the Ural Mou ...

( Kungurian) and/or basal

Guadalupian The Guadalupian is the second and middle Series (stratigraphy), series/Epoch (geology), epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico an ...

( 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 Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...

biozone In biostratigraphy, biostratigraphic units or biozones are intervals of geological strata that are defined on the basis of their characteristic fossil taxon, taxa, as opposed to a Lithostratigraphy, lithostratigraphic unit which is defined by the ...

s. 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,

Michel Laurin Michel Laurin is a Canadian-born French vertebrate paleontologist whose specialities include the emergence of a land-based lifestyle among vertebrates, the evolution of body size and the origin and phylogeny of lissamphibians. He has also made impo ...

and Robert W. Hook argued that the fusuline marine intercalation cited above does not belong to the San Angelo Formation in which it was mistakenly included, and cannot be used to date the latter. The name San Angelo Formation has been incorrectly applied to a wide variety of rocks in various

sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock They form when long-term subsidence ...

s located in western Texas, whereas the San Angelo Formation is restricted to the eastern shelf and is exclusively continental and devoid of marine fossils. On the other hand, the taxonomic revision of the ammonoids from the base of the Blaine Formation indicates a Roadian age rather than a Kungurian age and the San Angelo formation yielded a fossil flora dominated by voltzian

conifer Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...

s, an assemblage rather characteristic of the

and the

Lopingian The Lopingian is the uppermost series/last epoch of the Permian. It is the last epoch of the Paleozoic. The Lopingian was preceded by the Guadalupian and followed by the Early Triassic. The Lopingian is often synonymous with the informal te ...

. Thus, according to Laurin and Hook, the San Angelo Formation could date from latest Kungurian or earliest Roadian, or more likely could straddle the Kungurian/Roadian boundary. ''Cotylorhynchus bransoni'' is the youngest species of the genus and comes from the Chickasha Formation in Oklahoma. This formation was long considered contemporary with the San Angelo Formation. However, Laurin and Hook demonstrated that the Chickasha Formation is slightly younger because it is intercalated within the central part of the Flowerpot Formation, which overlies the Duncan Sandstone Formation, the latter being in fact the lateral equivalent of the San Angelo Formation in Oklahoma. Magnetostratigraphic data suggest that the Chickasha Formation probably dates from the early Roadian. A Roadian age was also suggested based on the presence in the Chickasha fauna of the nycteroleterid

parareptile Parareptilia ("near-reptiles") is an extinct group of Basal (phylogenetics), basal Sauropsida, sauropsids ("Reptile, reptiles"), traditionally considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds ...

'' Macroleter'', a genus that was only known from the Middle Permian of

European Russia European Russia is the western and most populated part of the Russia, Russian Federation. It is geographically situated in Europe, as opposed to the country's sparsely populated and vastly larger eastern part, Siberia, which is situated in Asia ...

. However, Sigi Maho and colleagues have pointed out that several genera of Permian

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

s had a wide temporal distribution, such as ''

Dimetrodon ''Dimetrodon'' ( or ; ) is an extinct genus of sphenacodontid synapsid that lived during the Cisuralian (Early Permian) Epoch (geology), epoch of the Permian period, around 295–272 million years ago. With most species measuring long and ...

'' 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). Additionally, probable nycteroleterid footprints, named ''Pachypes ollieri'', from Cisuralian rocks of Europe and North America and from the Guadalupian of Europe, show that the stratigraphic distribution of Nycteroleteridae was not restricted to the middle and late Permian but also included the early Permian. Cisuralian occurrences of ''P. ollieri'' come from the

Hermit A hermit, also known as an eremite (adjectival form: hermitic or eremitic) or solitary, is a person who lives in seclusion. Eremitism plays a role in a variety of religions. Description In Christianity, the term was originally applied to a Chr ...

(

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

), Rabéjac (

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

) and Peranera (

Spain Spain, or the Kingdom of Spain, is a country in Southern Europe, Southern and Western Europe with territories in North Africa. Featuring the Punta de Tarifa, southernmost point of continental Europe, it is the largest country in Southern Eur ...

) 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 North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

Paleoenvironments

In the Permian, most of the landmasses were united in a single supercontinent,

Pangea Pangaea or Pangea ( ) was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia (continent), Siberia during the Carboniferous period ...

. It was then roughly C-shaped: its northern (

Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...

) and southern (

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

) parts were connected to the west but separated to the east by the

Tethys Ocean The Tethys Ocean ( ; ), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean during much of the Mesozoic Era and early-mid Cenozoic Era. It was the predecessor to the modern Indian Ocean, the Mediterranean Sea, and the Eurasia ...

. 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 A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

and aeolian

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s deposited in a vast deltaic

plain In geography, a plain, commonly known as flatland, is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and ...

dotted with

lake A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...

s and

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...

s. This

coastal plain A coastal plain (also coastal plains, coastal lowland, coastal lowlands) is an area of flat, low-lying land adjacent to a sea coast. A fall line commonly marks the border between a coastal plain and an upland area. Formation Coastal plains can f ...

was bordered to the west by a sea that occupied what is today the

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

and the southernmost part of

. 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 A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in Atmosphere of Earth, atmospheric circulation and precipitation associated with annu ...

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

evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...

s indicates significant aridity interrupted by seasonal flooding.

Hennessey Formation

Everett C. Olson thought that the Hennessey Formation was represented by several sedimentary facies corresponding to several types of environments. According to him, part of the formation would have been deposited in a marine environment while other parts would represent coastal and continental deposits. The continental facies is mostly composed of red

s, locally accompanied by

lenses A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...

and beds of

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

s and

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

s interpreted as fluvial and floodplain deposits. However, detailed facies analyses later revealed that these rocks were more likely of aeolian origin, corresponding to

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

s, and

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

s deposited as

loess A loess (, ; from ) is a clastic rock, clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of Earth's land area is covered by loesses or similar deposition (geology), deposits. A loess ...

and sometimes trapped in mud flat, shallow salt lakes or wadi-type ephemeral streams. The fossils of ''Cotylorhynchus romeri'' are only found in red mudstones. This species occurs partly in the form of almost complete skeletons but also in the form of dislocated skeletons and articulated segments of skeletons. Based on the position of the articulated skeletons, Stovall and colleagues estimated that the animals were probably stuck in

marsh In ecology, a marsh is a wetland that is dominated by herbaceous plants rather than by woody plants.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p More in genera ...

es or

swamp A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...

s where they were buried. The dislocated or partially articulated skeletons also indicate that other specimens have undergone some transport prior to burial. According to Lambertz and colleagues, it is also possible that the animals became bogged down when the waterhole in which they lived dried up, in the hypothesis of a semiaquatic lifestyle in ''Cotylorhynchus''. Apart from ''C. romeri'', other known vertebrates in the Hennessey Formation are the

Captorhinidae Captorhinidae is an extinct family of tetrapods, traditionally considered primitive Reptile, reptiles, known from the late Carboniferous to the Late Permian. They had a cosmopolitan distribution across Pangea. Description Captorhinids are a cl ...

'' Captorhinikos chozaensis'' and '' Rhodotheratus parvus'', the

lungfish Lungfish are freshwater vertebrates belonging to the class Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, inc ...

'' Gnathorhiza'', and the

amphibian Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...

s '' Diplocaulus'', '' Brachydectes'', '' Rhynchonkos'', '' Aletrimyti'', and '' Dvellacanus''. ''Gnathorhiza'' and ''Brachydectes'' were able to aestivate in burrows during prolonged periods of aridity. Rare vertebrate tracks have been attributed to the ichnogenera '' Amphisauropus'' and '' Dromopus'', considered to be seymouriamorph amphibian and araeoscelid reptile footprints respectively. ''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

s and fine conglomerates. The central part of the formation consists mainly of red mudstones corresponding to

ey and

mud Mud (, or Middle Dutch) is loam, silt or clay mixed with water. Mud is usually formed after rainfall or near water sources. Ancient mud deposits hardened over geological time to form sedimentary rock such as shale or mudstone (generally cal ...

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 An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

s, and very shallow

sea A sea is a large body of salt water. There are particular seas and the sea. The sea commonly refers to the ocean, the interconnected body of seawaters that spans most of Earth. Particular seas are either marginal seas, second-order section ...

s 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

river A river is a natural stream of fresh water that flows on land or inside Subterranean river, caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of ...

s than those of the central part of the formation. However, in

, 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 Matrix (: matrices or matrixes) or MATRIX may refer to: Science and mathematics * Matrix (mathematics), a rectangular array of numbers, symbols or expressions * Matrix (logic), part of a formula in prenex normal form * Matrix (biology), the m ...

. Several bones indicate that some carcasses were partially devoured. The

taphonomy Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek language, Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientis ...

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. The fauna of the upper San Angelo Formation includes, among others, the caseid '' Caseopsis agilis'' and '' Angelosaurus greeni'', the sphenacodontid '' Dimetrodon angelensis'', the

captorhinids Captorhinidae is an extinct family of tetrapods, traditionally considered primitive reptiles, known from the late Carboniferous to the Late Permian. They had a cosmopolitan distribution across Pangea. Description Captorhinids are a clade of sm ...

'' Rothianiscus multidonta'', and '' Kahneria seltina'', and the tupilakosaurid dvinosaur '' Slaugenhopia''. A few tetrapod tracks also indicate the presence of a nycteroleterid pareiasauromorpha (

ichnotaxon An ichnotaxon (plural ichnotaxa) is "a taxon based on the fossilized work of an organism", i.e. the non-human equivalent of an artifact. ''Ichnotaxon'' comes from the Ancient Greek (''íchnos'') meaning "track" and English , itself derived from ...

''Pachypes ollieri''), a partial skeleton of which is known from slightly younger deposits of the Chickasha Formation. Unusual flora has been found in the channels of the upper San Angelo formation. It is dominated by

gymnosperm The gymnosperms ( ; ) are a group of woody, perennial Seed plant, seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include Pinophyta, conifers, cycads, Ginkgo, and gnetoph ...

s and is remarkable for its unique composition including both typical Lower Permian taxa such as ''

Walchia ''Walchia'' is a primitive fossil conifer found in upper Pennsylvanian (geology), Pennsylvanian (Carboniferous) and lower Permian (about 310-290 Mya (unit), Mya) rocks of Europe and North America. A forest of In situ, in-situ Walchia tree-stumps ...

'' or '' Culmitzschia'' but also forms that were previously known only in middle or late Permian rocks as various species of '' Ulmannia'', '' Pseudovoltzia liebeana'', and the taxon of uncertain affinity '' Taeniopteris eckardtii'', or in

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

strata such as the bennettitale '' Podozamites'' and the putative Cycadidae '' Dioonitocarpidium''. The rest of the flora is represented by the ginkgoale '' Dicranophyllum'', the cordaitale '' Cordaites'', and the equisetale cf. '' Neocalamites''.

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

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...

s 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''. Elsewhere in this formation are known the xenacanth '' Orthacanthus'', the Nectridea '' Diplocaulus'', the dissorophid

temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') or temnospondyls is a diverse ancient order (biology), order of small to giant tetrapods—often considered Labyrinth ...

'' Nooxobeia'', the nycteroleterid '' Macroleter'' and the

varanopids Varanopidae is an extinct family of amniotes known from the Late Carboniferous to Middle Permian that resembled monitor lizards (with the name of the group deriving from the monitor lizard genus ''Varanus'') and may have filled a similar niche. T ...

'' Varanodon'' and '' Watongia ''.