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tritylodontidae
Tritylodontids ("three knob teeth", named after the shape of animal's teeth) were small to medium-sized, highly specialized and extremely mammal-like cynodonts. They were the last known family of the non-mammalian synapsids. One of the last cynodont lines to appear, the Tritylodontidae descended from a ''Cynognathus''-like cynodont. The Tritylodontids were herbivorous, chewing through vegetation, such as stems, leaves, and roots.
==Description==
The tritylodont's skull had a high flat crest. They retained the reptilian joint between the quadrate bone of the skull and the auricular bone of the lower jaw, but they were reduced. It is only through the retention of the vestigial reptilian jawbones that they are technically regarded to not be mammals. The back of the skull had huge zygomatic arches for the attachment of its large jaw muscles. They also had a very well-developed secondary palate. The tritylodont dentition was very different from that of other cynodonts. They did not have canines. The front pair of incisors were enlarged that were very similar to rodents of today. Traversodonts had a large gap, the diastema, that separated the incisors from the square-shaped cheek. Each of the cheek teeth in the upper jaw had three rows of cusps running along its length that had grooves in between. The lower teeth had two rows of cusps which fitted into the grooves in the upper teeth. The matching of the cusps allowed the teeth to meet in a precise bite. It would grind its food between the teeth in somewhat the same way that a modern rodent would with their food. The teeth were well suited for shredding plants matter. Like Mammaliformes, tritylodontids have epipubic bones, a possible synampomorphy between both clades,〔Stephen Reily and Thomas White, Hypaxial Motor Patterns and the Function of Epipubic Bones in Primitive Mammals, ARTICLE in SCIENCE 299(5605):400-2 · FEBRUARY 2003, Department of Biological Sciences, Ohio University, Athens, OH 45701, USA.
Impact Factor: 33.61 · DOI: 10.1126/science.1074905 · Source: PubMed〕 and as such were forced to produce undeveloped fetus-like young like modern monotremes and marsupials.
The Tritylodonts can very much be seen as Mesozoic rodents. Tritylodonts were active animals that were probably warm blooded and burrowed like modern day rodents. For example, Oligokyphus could be compared to a weasel or mink, with a long, slim body and tail. Its legs had evolved directly beneath the body, as they have in mammals.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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