Tritylodontidae

Taxobox
name = Tritylodonts
fossil_range = Late Triassic - mid Cretaceous

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image_width = 240px
image_caption = "Oligokyphus"
regnum = Animalia
phylum = Chordata
classis = Synapsida
ordo = Therapsida
subordo = Cynodontia
infraordo = Eucynodontia
unranked_familia = Cynognathia
superfamilia = Tritylodontoidea
familia = Tritylodontidae
familia_authority = Cope, 1884
subdivision_ranks = Genera
subdivision =See "Genera"

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 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. Some scientists believe that the mammals arose from this group of cynodonts, however, some say that mammals arose from the Trithelodontidae, another group of specialized cynodonts. One of the interesting facts about the Tritylodontids is that they are the longest living of all the non-mammalian therapsids. They appeared in the latest Triassic period, and persisted well into the Jurassic until the Middle Cretaceous. This shows that the Tritylodontids were a very successful group of therapsids, even though they lived right beneath the ruling dinosaurs' feet. No one knows why the Tritylodontids went extinct by the Middle Cretaceous. Perhaps the Tritylodontids were outcompeted by their relatives, the mammals. Some mammals have developed herbivory during the Late Jurassic and Cretaceous. Or, the Tritylodontids may have gone extinct because of the new plant group, the angiosperms or flowering plants because they aren't used to eating new type of plants. "Chronoperates" may be one exception, it may be a Tritylodontid, and it lived in the Paleocene, long after the Middle Cretaceous, and after the Cretaceous–Tertiary extinction event. If true, then the Tritylodontids were elusive and rare during the Late Cretaceous, because no Tritylodonts were found by that time. However, the "Chronoperates" 's anatomy almost closely resembles to that of symmetrodonts - a mammalian lineage. It is very clear that the Tritylodontids were warm-blooded. The Tritylodontid fossils were found in the Americas, South Africa, and Eurasia. They may have managed to live worldwide, including Antarctica.

Genera

*"Bienotherium"
*"Bocatherium"
*"Dianzhongia"
*"Kayentatherium"
*"Lufengia"
*"Oligokyphus"
*"Stereognathus"
*"Tritylodon"
*"Xenocretosuchus"
*"Yunnanodon" ----The Tritylodonts can very much be seen as Mesozoic rodents. The appearance of these animals can be compared to that of a mink, weasel, otter, the hare, and the ferret.

The Tritylodontidae were mammal-like herbivorous cynodont synapsids. The tritylodonts were among the last of the cynodonts, which evolved from the Traversodontidae in latest Triassic period, and their lineage survived into the Jurassic period. They were the longest-lived group of all the therapsids and along with the Trithelodontidae (Ictidosaurs) the only mammal-like reptiles to endure into the Jurassic period, and the only non-mammalian Theropsida (Synapsida) to survive into the late Jurassic period.

The tritylodontids are the resolute of the evolution of the herbivorous cynodont. Complete specimens, were found in South Africa, East Asia, Europe, North & South America.

The Tritylodont was first discovered in the Upper Triassic rocks of South Africa in the late 1800’s. It was thought to be one of the very earliest mammals. For example, one of the tritylodontids, a 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.

The tritylodont's skull had a high flat crest. 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 dentition of these animals 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. Primitive rodents, 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.

They were active animals that were probably warm blooded and burrowed like modern day rodents. 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 as reptiles.

See also

*Cynodontia
*Cynognathia
*Trithelodontidae
*Mammalian embryonic diapause