Trithelodonta

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Trithelodonta
Pachygenelus

Pachygenelus

Temporal occurrence
Upper Triassic to Lower Jurassic
228 to 190.8 million years
Locations
Systematics
Synapsids (Synapsida)
Therapsids (Therapsida)
Theriodontia
Cynodontia
Eucynodontia
Trithelodonta
Scientific name
Trithelodonta
Broom , 1912

The Trithelodonta, also called Ictidosauria (weasel lizards), are land vertebrates from the group of therapsids ("mammal-like reptiles"). They mainly include small insectivorous forms. Along with the Tritylodontidae , they are the group that most closely resembled mammals .

features

The trithelodonta were rather small, but only their three to six centimeters long skulls are well known. Only a few fragments of the postcranial skeleton have been preserved in fossil form. The humerus and femur of Pachygenelus are very similar to those of the basal mammal Morganucodon .

From the skull bones they had lost the prefontale and the postorbiltale and therefore the orbitals were not separated from the skull windows. In contrast to the Tritylodontidae, their skull window was elongated, the sagittal ridge wide and low. The trithelodonta had a double mandibular joint, the more modern secondary mandibular joint consisting of the dentale and the squamosum in front, the old reptilian joint of the articular and the quadratum in the rear.

The main feature for the determination of the Trithelodonta is the specialized dentition, in which they can also be distinguished from the Tritylodontidae. In Pachygenelus there are only two incisors in the upper and lower jaw. The canines correspond to those of the other cynodonts .

Systematics

Kuhn still considered the trithelodonta to be descendants of the Bauriamorpha . Today, however, like the Tritylodontidae, they are regarded as derived cynodonts.

Genera

literature