The Trithelodontidae, also known as Ictidosaurs, were small to medium-sized cynodonts. They were extremely mammal-like, highly specialized cynodonts, although they still retained a very few reptilian anatomical traits. They descended from a basal Eucynodont therapsid, something more or less like Cynognathus. They were mainly carnivorous or insectivorous, though some species may have developed omnivorous traits. Their skeletons show that they had a close relationship to mammals. Some scientists feel that the Trithelodontidae stem or its closest relatives may have given rise to primitive mammals. The trithelodontids were one of the longest lived non-mammalian therapsids, living from the late Triassic to the Jurassic period. It is unknown why these specialized cynodonts became extinct during the Jurassic period. One possible explanation is that they lost out to competition with a related group, the mammals. Most mammals were carnivorous during the Jurassic and they may have preyed upon the trithelodontids. One group of mammals, the Triconodonts, which began to appear in Late Jurassic were carnivorous, and they may have eaten almost anything small, such as the endangered trithelodontids. They are known from finds in South America and South Africa, indicating that they only lived on supercontinent of Gondwanaland.

Phylogeny & Genera

• Riograndia (a primitive Trithelodontid)
• Subfamily Thrithelodontinae
• Chalimia
• Elliotherium
• Diarthrognathus
• Irajatherium
• Trithelodon
• Pachygenelus

See also

• Tritylodontidae
• Cynodonts