Cotylorhynchus

Cotylorhynchus
Temporal range: Kungurian, 279.5–272 Ma
Mounted skeleton of C. romeri
Scientific classification
Kingdom:Animalia
Phylum:Chordata
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 is an extinct genus of very large synapsids 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]

Description

C. romeri restoration

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.

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.

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.

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 its 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

Restoration of C. hancocki
Size comparison

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

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. 1 2 "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. 1 2 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.
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