Caseasauria

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Caseasaurs
Temporal range: Early Permian - Middle Permian
Cotylorhynchus romeri.jpg
Fossil skeleton of Cotylorhynchus romeri
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Clade: Caseasauria
Genera and Families

Caseidae
Eothyrididae
?Phreatophasma

Caseasauria is one of the two main clades of early synapsids, the other being the Eupelycosauria. Caseasaurs are currently known only from the Permian, and include two superficially different families, the small insectivorous or carnivorous Eothyrididae, and the large herbivorous Caseidae. These two groups share a number of specialised features associated with the morphology of the snout and external naris.

The ancestor of caseasaurs can be traced back to an insect eating or an omnivorous reptile-like synapsid from the Pennsylvanian time of the Carboniferous, possibly resembling Archaeothyris, the earliest known synapsid. The caseasaurs were abundant during the later part of the Early Permian, but by the Middle Permian caseasaur diversity declined because the group was outcompeted by the more successful therapsids. The last caseasaurs became extinct at the end of the Guadelupian (Middle Permian).[1]

Phylogeny[edit]

Most uncertainty in the phylogeny of synapsids lies among the earliest members of the group, including forms traditionally placed within Pelycosauria. As one of the earliest phylogenetic analyses, Brinkman & Eberth (1983) placed the family Varanopidae with Caseasauria as the most basal ofshoot of the synapsid lineage. Reisz (1986) removed Varanopidae from Caseasauria, placing it in a more derived position on the stem. While most analyses find Caseasauria to be the most basal synapsid clade, the analysis of Benson (2012) placed a clade containing Ophiacodontidae and Varanopidae as the most basal synapsids, with Caseasauria occupying a more derived position. Benson attributed this revised phylogeny to the inclusion of postcranial characteristics, or features of the skeleton other than the skull, in his analysis. When only cranial or skull features were included, Caseasauria remained the most basal synapsid clade. Below is a cladogram modified from the analysis of Benson (2012):[2]



Tseajaia campi



Limnoscelis paludis


Amniota


Captorhinus spp.



Protorothyris archeri



Synapsida


Ophiacodontidae



Varanopidae




Eupelycosauria

Ianthodon schultzei




Edaphosauridae


Sphenacodontia

Haptodus garnettensis




Pantelosaurus saxonicus




Therapsida



Sphenacodontidae







Caseasauria
Eothyrididae

Eothyris parkeyi



Oedaleops campi



Caseidae

Oromycter dolesorum




Casea broilii




Trichasaurus texensis




Euromycter rutenus (="Casea" rutena)




Ennatosaurus tecton




Angelosaurus romeri




Cotylorhynchus romeri




Cotylorhynchus bransoni



Cotylorhynchus hancocki















See also[edit]

References[edit]

  1. ^ Maddin, H.C., Sidor, C.A. & Reisz, R.R. 2008. Cranial anatomy of Ennatosaurus tecton (Synapsida: Caseidae) from the Middle Permian of Russia and the evolutionary relationships of Caseidae. Journal of Vertebrate Paleontology (28): 160-180
  2. ^ Benson, R.J. (2012). "Interrelationships of basal synapsids: cranial and postcranial morphological partitions suggest different topologies". Journal of Systematic Paleontology. in press. doi:10.1080/14772019.2011.631042. 

External links[edit]