Cotylorhynchus

Cotylorhynchus Temporal range: Kungurian, 279.5–272 Ma PreЄ Є O S D C P T J K Pg N
Mounted skeleton of C. romeri
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Clade:	†Caseasauria
Family:	†Caseidae
Genus:	†Cotylorhynchus Stovall, 1937
Type species
†Cotylorhynchus romeri Stovall, 1937
Species
C. romeri Stovall, 1937 C. hancocki Olson & Beerbower, 1953 C. bransoni Olson & Barghusen, 1962

Cotylorhynchus was a very large synapsid that lived in the southern part of what is now North America during the Early Permian period.^[1] It is the best known member of the synapsid clade Caseidae, usually considered the largest terrestrial vertebrates of the Early Permian,^[2] though they were possibly aquatic.^[3]

Life reconstruction of Cotylorhynchus romeri

Description

Size

Cotylorhynchus was a heavily built animal with a disproportionately small head and a huge barrel-shaped body. Adults of the species C. romeri were about 3 m (9.8 ft)^[4] while those of the younger C. hancocki were around 20-25% larger in linear measurements,^[5] making it one of the largest synapsids of the early Permian.

Skull

Their skulls are distinctive in the presence of large temporal openings and very large nostril openings, which could have been utilized for better breathing or may have housed some sort of sensory or moisture conserving organ. Also they featured large pineal openings and a snout or upper jaw that overhangs the row of teeth to form a projecting rostrum. Rounded deep pits and possibly large depressions were present on the outer surface of the skull. Their teeth were very similar to those of iguanas with posterior marginal teeth that bore a longitudinal row of cusps.

Restoration of Cotylorhynchus

Limbs

Their skeletal features included a massive scapulocoracoid, humeri with large flared ends, stout forearm bones and broad, robust hands that had large claws. Certain features of their hands indicate that they were paddle-like in shape and structure, being used to swim in a manner much similar to that of modern turtles.^[6]

Their digits were believed to have a considerable range of motion and large retractor processes on the ventral surfaces of the unguals allowed them to flex their claws with powerful motions. Also, the articulatory surfaces of their phalanges were oblique to the bone's long axis rather than perpendicular to it. This allowed for much more surface area for the flexor muscles.

Diaphragm

Cotylorhynchus shows evidence indicative of a diaphragm. Unlike that of modern mammals it was probably weak and necessitating support from other muscle groups, a deficiency exacerbated by it's aquatic habits.^[6]

Discovery

C. romeri fossil

Cotylorhynchus were considered a part of the first wave of amniote diversity. There have been three species of Cotylorhynchus discovered: C. hancocki, C. romeri^[7] and C. bransoni. C. hancocki is believed to be a descendent of the slightly smaller C. romeri.

• Various skeletal parts of C. romeri have been found around central Oklahoma^[4] in parts of Cleveland County.
• Parts of C. hancocki have been found in northern Texas in Hardeman and Knox counties.
• C. bransoni specimens have been uncovered in Kingfisher and Blaine Counties of central-northwest Oklahoma.

Classification

Cotylorhynchus belongs to the family Caseidae, a family of massively built synapsids with small heads and barrel-like bodies. It was a derived member of Caseidae. It is a sister taxon of Angelosaurus.

Below is a cladogram by Maddin et al. in 2008.^[8]

Caseasauria	Eothyris  Caseidae  Oromycter  Casea  Ennatosaurus  Cotylorhynchus  Angelosaurus

See also

• List of synapsids

References

1. Maddin, Hillary C.; Sidor, Christian A.; Reisz, Robert R. (2008). "Cranial Anatomy of Ennatosaurus tecton (Synapsid: Caseidae) From the Middle Permian of Russia and the Evolutionary Relationships of Caseidae". Journal of Vertebrate Paleontology. 28 (1): 161. doi:10.1671/0272-4634(2008)28[160:CAOETS]2.0.CO;2.
2. "Caseasauria". Retrieved 27 August 2012.
3. Lambertz, M.; Shelton, C.D.; Spindler, F.; Perry, S.F. (2016). "A caseian point for the evolution of a diaphragm homologue among the earliest synapsids". Annals of the New York Academy of Sciences. doi:10.1111/nyas.13264.
4. "Fossil Evidence Permian". Smithsonian National Museum of Natural History. Retrieved 27 August 2012.
5. Olson, Everett C. (1962). "Late Permian Terrestrial Vertebrates, U. S. A. and U. S. S. R". Transactions of the American Philosophical Society. 52 (2). JSTOR 1005904.
6. Markus Lambertz et al, A caseian point for the evolution of a diaphragm homologue among the earliest synapsids, Annals of the New York Academy of Sciences (2016). DOI: 10.1111/nyas.13264
7. Stovall, J. Willis; Price, Llewellyn; Romer, Alfred (1966). "The Postcranial Skeleton of the Giant Permian Pelycosaur Cotylorhynchus romeri" (PDF). Bulletin of the Museum of Comparative Zoology. 135 (1). Retrieved 27 August 2012.
8. Maddin; et al. (2008). "Cranial anatomy of "Ennatosaurus tecton" (Synapsida: Caseidae) from the middle permian of russia and the evolutionary relationships of Caseidae" (PDF): 173. Retrieved 26 November 2013.