Tritylodontidae

Yunnanense skull of Bienotherium

• Worldwide

The Tritylodontidae were a group of herbivorous Cynodonten. They lived on the Upper Triassic to Lower Cretaceous probably, but at least until the Middle Jurassic. They are the longest surviving therapsids that are not mammals (if you're a relic of occurrence of Dicynodontia in Australia, to the Lower Cretaceous, aside ).

The first tritylodontiden teeth were made ​​in 1847 and 1866 in the upper layers of the Keuper of Württemberg and interpreted as the oldest fossils of mammals. The finds were described under the name Microlestes and Triglyphus. They are probably identical with Tritylodon whose teeth and skull fragments were found in the South African Karoo and were described in 1884 by Richard Owen.

Fossils of various other genera have been found in southern Africa, Europe and North America. From South America, China and the Mount Kirkpatrick in Antarctica derived fossils of uncertain assignment. Isolated tritylodontide teeth from Russia come from the Lower Cretaceous.

Features

The skull of Tritylodontidae is very similar to mammals. The cranial windows are large and go, because of the missing bone clasp ( postorbital clasp ), directly into the bony eye socket (orbit ) over.

The teeth superficially resembles that of the rodents and the Multituberculata and is specialized for a vegetable diet. The similarity, however, is created by a convergent probably similar diet and not based on closer relationship. Canines are missing and functionally enlarged by a pair of incisors were replaced. Between cutting and the complex, molarähnlichen molars are in upper and lower jaw a distinct diastema (Greek for "space" ). The molars have two roots. In the maxilla, they carry three, in the lower jaw two longitudinal rows of bumps that grip mouth closed in the ranks of the upper jaw. Tritylodontidae had two dentitions ( Diphyodontie ).

Primitive features are the lower jaw joint that is not formed as in mammals of Dental and squamosal, but as with the reptiles of the quadrate and articular. The ossicles are built nor easy. At the shoulder belt is still an intermediate collarbone ( interclavicle ) and a coracoid ( coracoid ) available.

The skulls are five ( Bocatherium ) to 25 centimeters ( Kayentatherium and Tritylodon ) long. Also the rest of the skeleton, which is mainly known by Oligokyphus is very similar to mammals.

System

In the 19th century Tritylodontidae were expected to mammals and even today the view is still held that they are mammals of all therapsids the next. Because of their teeth specializations ( loss of the canine, cusp structure) they do not come, however, as the direct ancestors of the mammals in question. Some scholars are of the opinion that they are the sister group.

• Tritylodontidae Oligokyphus
• Tritylodon
• Bienotherium
• Kayentatherium
• Lufengia
• Dianzhongia
• Bocatherium
• Yunnanodon
• Stereognathus
• Xenocretosuchus