Belongs within: Theriodontia.
Contains: Probainognathia.
The clade Cynodontia, incluing modern mammals and a number of related non-mammalian synapsids, was defined by Hopson & Kitching (2001) as the most inclusive clade including Mammalia and excluding Bauria. Though the group was ancestrally carnivorous, herbivory evolved among the cynodonts in the Gomphodontia and the Tritylodontidae (as well as several times within the mammals). Cynodonts are first known from the Late Permian, where they are represented by Dvinia and the Procynosuchidae. The remaining cynodonts form a clade Epicynodontia, defined as all taxa closer to mammals than Procynosuchidae and united by synapomorphies including a dentary-surangular dorsal contact midway between the postorbital bar and jaw joint, a coronoid process on the dentary extending above the middle of the orbit, four upper incisors and three lower incisors (Hopson & Kitching 2001).
Characters (from Hopson & Kitching 2001): Nasal-lacrimal contact present; postfrontal absent; prefrontal-postorbital contact present; ectopterygoid not in contact with maxilla; palatal exposure of maxilla behind canine greater than 20% distance from canine to posterior end of palatine; secondary palatal plate on maxilla and palatine; pterygoid flange without teeth; tabular extending around posttemporal foramen; groove on prootic extending from pterygoparoccipital foramen to trigemimal foramen; trigeminal nerve exiting via foramen between prootic and epipterygoid; posteroventral process on quadrate in posterior notch of squamosal; ascending process of epipterygoid greatly expanded; epipterygoid overlapping prootic; lateral flange present on prootic; epipterygoid in contact with frontal; double occipital condyles; stapedial foramen with dorsoventral orientation; dentary masseteric fossa present high on coronoid region; dentary overlap of surangular long; reflected lamina of angula spoon-shaped plate; incisor cutting margins smoothly ridged; canine serrations absent; postcanines with two or more cusps in line; lower anterior cingulum or cusp present; anterior process of ilium 1.0 to 1.5 times diameter of acetabulum; pubis between 1.5 and 1.0 times acetabular diameter.
Cynodontia
| i. s.: Chronoperates paradoxus Fox, Youzwyshyn & Krause 1992SFY02
|--Dvinia [Dviniidae]HK01
| `--D. prima Amalitzky 1922B93
`--+--ProcynosuchidaeTT05
| |--Uralocynodon tverdochlebovae (Tatarinov 1987)TT05
| `--Procynosuchus Broom 1931MH06, D07
| |--P. delaharpeae Broom 1937B93
| `--P. rubidgeiD07
`--EpicynodontiaHK01
|--GalesauridaeCE57
| |--Galesaurus planiceps Owen 1859HK01, B93
| |--SysphinctosomaCE57
| |--CistecynodonCE57
| `--Cynosaurus suppostus (Owen 1876)B93
`--+--Thrinaxodon Seeley 1894MH06, D07 [Thrinaxodontidae]
| `--T. liorhinus Seeley 1894B93
`--Eucynodontia [Tritylodontoidea]HK01
|--CynognathiaHK01
| |--CynognathidaeHK01
| | |--Cynognathus Seeley 1895D07
| | | |--C. crateronotus Seeley 1895B93
| | | `--C. minor Bonaparte 1967B93
| | `--Cynidiognathus longiceps Boonstra 1947C69
| `--Gomphodontia [Diademodontidae, Traversodontidae]HK01
| | i. s.: Scalenodontoides Crompton & Ellenberger 1957CE57
| | `--*S. macrodontes Crompton & Ellenberger 1957CE57
| | ProtacmonCE57
| | Andescynodon mendozensis Bonaparte 1967B93
| | Ruscionodon mignonei Bonaparte 1972B93
| | Microscalenodon nanus Hahn et al. 1988B93
| | Menadon besairieiKN20
| | Dadadon isaloiKN20
| |--DiademodonHK01
| | |--D. grossarthi (Broili & Schröder 1935)B93
| | |--D. mastacus Seeley 1894B93
| | |--D. rhodesiensis Brink 1963B93
| | `--D. tetragonus Seeley 1894B93
| `--+--TrirachodontidaeB93
| | |--Trirachodon berryi Seeley 1894HK01, B93
| | `--Cricodon metabolus Crompton 1955B93
| `--+--Pascualgnathus polanskii Bonaparte 1966HK01, B93
| `--+--Scalenodon angustifronsHK01
| `--+--Luangwa drysdallensis Brink 1963HK01, C69
| `--+--Massetognathus Romer 1967HK01, D07
| | |--M. ochagaviaeD07
| | `--M. pascualiD07
| `--+--‘Scalenodon’ hirschoniHK01
| `--+--ExaeretodonHK01
| `--Gomphodontosuchus [Gomphodontosuchidae]HK01
`--ProbainognathiaHK01
*Type species of generic name indicated
References
[B93] Benton, M. J. 1993. Reptilia. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 681–715. Chapman & Hall: London.
[C69] Cox, C. B. 1969. Two new dicynodonts from the Triassic Ntawere Formation, Zambia. Bulletin of the British Museum (Natural History): Geology 17 (6): 255–294.
[CE57] Crompton, A. W., & F. Ellenberger. 1957. On a new cynodont from the Molteno Beds and the origin of the tritylodontids. Annals of the South African Museum 44 (1): 1–14.
[D07] Dixon, D. 2007. The Complete Illustrated Encyclopedia of Dinosaurs & Prehistoric Creatures. Hermes House: London.
[HK01] Hopson, J. A., & J. W. Kitching. 2001. A probainognathian cynodont from South Africa and the phylogeny of nonmammalian cynodonts. Bulletin of the Museum of Comparative Zoology 156 (1): 5–35.
[KN20] Kammerer, C. F., S. J. Nesbitt, J. J. Flynn, L. Ranivoharimanana & A. R. Wyss. 2020. A tiny ornithodiran archosaur from the Triassic of Madagascar and the role of miniaturization in dinosaur and pterosaur ancestry. Proceedings of the National Academy of Sciences of the USA 117 (30): 17932–17936.
[MH06] Meng, J., Y. Hu, Y. Wang, X. Wang & C. Li. 2006. A Mesozoic gliding mammal from northeast China. Nature 444 (7121): 889–893.
[SFY02] Scott, C. S., R. C. Fox & G. P. Youzwyshyn. 2002. New earliest Tiffanian (late Paleocene) mammals from Cochrane 2, southwestern Alberta, Canada. Acta Palaeontologica Polonica 47: 691–704.
[TT05] Tverdokhlebov, V. P., G. I. Tverdokhlebova, A. V. Minikh, M. V. Surkov & M. J. Benton. 2005. Upper Permian vertebrates and their sedimentological context in the South Urals, Russia. Earth-Science Reviews 69: 27–77.