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''Tritylodon'' (Greek for 3 cusped tooth) is an extinct genus of tritylodonts, one of the most advanced group of
cynodont The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...
therapsids. They lived in the Early Jurassic and possibly Late Triassic periods along with dinosaurs. They also shared many characteristics with
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s, and were once considered mammals because of overall skeleton construction. That was changed due to them retaining the vestigial reptilian jawbones and a different skull structure. Tritylodons are now regarded as non-mammalian synapsids.


Characteristics

If a living ''Tritylodon'' were to be seen today, it would look a lot like a large rodent. They were about long but there is no certainty about the exact weight. Their method of chewing food, a grinding motion with the bottom teeth sliding against the top teeth, resembled that of rodents as well. The bottom teeth were much like a set of cusps and the top teeth were a set of matching grooves that matched perfectly allowing this motion. There were large incisors at the very front of their mouth separated by a gap from the rest of the teeth. The incisors would stick out and remain slightly visible when the mouth was closed. The legs were directly beneath the body like mammals, unlike the earlier therapsids with sprawling limbs. These animals were burrowers; the structure of the shoulder, front limbs, and large front incisors show this. They used their incisors to help dig and unearth buried plants. The way they ate and the shape of their teeth demonstrate that ''Tritylodons'' were probably primarily herbivorous (though some tritylodontids show evidence of more omnivorous diets, and modern analogues like
rodents Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are nat ...
tend to be more omnivorous than their dentitions lead on). Any of the Tritylodonts including ''Tritylodon'' were warm-blooded or endothermic. Like most non- placental mammalimorphs, it had epipubic bones, aiding in its erect gait but preventing the expansion of the abdomen, making it unable to go through prolonged pregnancy and instead give birth to larval young like modern
marsupials Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a po ...
and monotremes.


Habitat

The ''Tritylodons habitat was limited to the forests of South Africa, with other fossils found in the
Hanson Formation The Hanson Formation (also known as the Shafer Peak Formation) is a geologic formation on Mount Kirkpatrick and north Victoria Land, Antarctica. It is one of the two major dinosaur-bearing rock groups found on Antarctica to date; the other is the ...
of Antarctica. When the species originated, about 200 million years ago, the African area was drier and hotter. But for most of their existence the climate was tropical and wetter.


Fossils

The ''Tritylodon'' fossils in South Africa are found concentrated mainly in an area about 11,000 km² (4,250 mi²). They have been found in floodplain deposits of the Lower Jurassic Elliot Formation (upper
Karoo Supergroup The Karoo Supergroup is the most widespread stratigraphic unit in Africa south of the Kalahari Desert. The supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Late Carboniferous and Early Jurassic, a perio ...
). In this area there have been so many findings it has been named the Tritylodon Acme Zone. The fossil findings have all been in the Free State of South Africa. The genus ''Tritylodon'' of the Tritylodonts is restricted to the South African forms: ''Tritylodon longaevus'' and ''Tritylodon maximus''. It is suggested that ''T. maximus'' is either a large ''T. longeavus'' or a closely related species. If it is a closely related species it could possibly be ecological succession since the larger ''T. maximus'' fossils have been dated in the Sinemurian–Pliensbachian mainly less than 190 million years ago and the ''T. longaevus'' in the Hettangian–Sinemurian mainly more than 190 million years ago. With the fossil findings of each species overlapping in Sinemurian stage, the fossils show two differences, ''T. maximus'' being larger and having nine upper postcanines (neither species had canine teeth) instead of the seven teeth like ''T. longeavus''. All other structures of the two ''Tritylodon'' species were the same.http://home.arcor.de/ktdykes/jtherap.htm#tritylodon Below is a cladogram from Ruta, Botha-Brink, Mitchell and Benton (2013) showing one hypothesis of cynodont relationships:


References


External links

* * * * *https://archive.today/20130204222846/http://tritylodontidae.totallyexplained.com/ * {{Taxonbar, from=Q1441437 Prehistoric cynodont genera Jurassic synapsids of Africa Fossil taxa described in 1884 Taxa named by Richard Owen Tritylodontids