Gomphodontia

Gomphodontia Temporal range: Early Triassic - Early Jurassic
Skull of the gomphodont Diademodon tetragonus
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Order:	Therapsida
Suborder:	Cynodontia
(unranked):	†Cynognathia
Stem group:	†Gomphodontia Seeley, 1895

Gomphodontia is a clade of cynognathian cynodonts that includes the families Diademodontidae, Trirachodontidae, and Traversodontidae. Gomphodonts are distinguished by wide and closely spaced molar-like postcanine teeth, which are convergent with those of mammals. Other distinguishing characteristics of gomphodonts include deep zygomatic arches, upper postcanines with three or more cusps spanning their widths and lower postcanines with two cusps spanning their widths.^[1] Gomphodonts first appeared in the Early Triassic and became extinct in the Jurassic. Fossils are known from southern Africa, Argentina and southern Brazil (Paleorrota geopark), eastern North America, Europe, China, and Antarctica.

Gomphodontia was first named by paleontologist Harry Seeley in 1895.^[2] He considered it an order of wide-toothed therapsids (then called anomodonts) from South Africa, distinct from Cynodontia. By the 1930s Gomphodontia was considered a suborder of Cynodontia and included the families Diademodontidae, Trirachodontidae, Traversodontidae, and Tritylodontidae.^[3] These four families have also been grouped in the superfamily Traversodontoidea, named by paleontologist Edward Drinker Cope in 1884. Tritylodontoidea has occasionally replaced Gomphodontia in various cynodont taxonomies. In 2001 Gomphodontia was defined as a stem-based clade including all cynodonts more closely related to Exaeretodon than to Cynognathus.^[4] This placed it within the larger clade Cynognathia, one of the two main groups of eucynodonts (the other being Probainognathia). Since then most studies have removed Tritylodontidae from Gomphodontia and reclassified it within Probainognathia as a group more closely related to mammals than are the convergently similar gomphodonts. Tritylodontoidea has fallen into disuse while Gomphodontia continues to be used in many studies.

Cladogram

Below is a cladogram from Ruta, Botha-Brink, Mitchell and Benton (2013) showing one hypothesis of cynodont relationships:^[5]

Cynodontia	Charassognathus Dvinia Procynosuchus  Epicynodontia  Cynosaurus Galesaurus Progalesaurus Nanictosaurus Thrinaxodon Platycraniellus  Eucynodontia  Cynognathia → Probainognathia →

→ Cynognathia

Cynognathus  Gomphodontia  Diademodon  Trirachodontidae  Beishanodon Sinognathus Trirachodon Cricodon Langbergia  Traversodontidae  Andescynodon Pascualgnathus Scalenodon Luangwa Traversodon "Scalenodon" attridgei Mandagomphodon Nanogomphodon Arctotraversodon Boreogomphodon  Massetognathinae  Massetognathus Dadadon Santacruzodon  Gomphodontosuchinae  Menadon Gomphodontosuchus Protuberum Exaeretodon Scalenodontoides

→ Probainognathia	Lumkuia Ecteninion Aleodon Chiniquodon Probainognathus Trucidocynodon Therioherpeton  Tritheledontidae  Riograndia Chaliminia Elliotherium Diarthrognathus Pachygenelus  Brasilodontidae  Brasilitherium Brasilodon  Tritylodontidae  Oligokyphus Kayentatherium Tritylodon Beinotherium  Mammaliaformes  Sinoconodon Morganucodon

References

1. Sues, H. D.; Hopson, J. A. (2010). "Anatomy and phylogenetic relationships ofBoreogomphodon jeffersoni(Cynodontia: Gomphodontia) from the Upper Triassic of Virginia". Journal of Vertebrate Paleontology. 30 (4): 1202. doi:10.1080/02724634.2010.483545.
2. Seeley, H. G. (1895). "Researches on the Structure, Organization, and Classification of the Fossil Reptilia. Part IX., Section 4. On the Gomphodontia". Philosophical Transactions of the Royal Society of London. B. 186: 1–57. JSTOR 91793.
3. Parrington, F.R. (1936). "On the Tooth-Replacement in Theriodont Reptiles". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 226 (532): 121–142. doi:10.1098/rstb.1936.0005. JSTOR 92294.
4. Hopson, J.A.; Kitching, J.W. (2001). "A probainognathian cynodont from South Africa and the phylogeny of nonmammalian cynodonts". Bulletin of the Museum of Comparative Zoology. 156 (1): 5–35.
5. Ruta, M.; Botha-Brink, J.; Mitchell, S. A.; Benton, M. J. (2013). "The radiation of cynodonts and the ground plan of mammalian morphological diversity". Proceedings of the Royal Society B: Biological Sciences. 280 (1769): 20131865. doi:10.1098/rspb.2013.1865.