Shuotherium dongi, n. gen. and sp. , a therian with pseudo-tribosphenic molars from the Jurassic of Sichuan, China.

Abstract

Shuotherium dongi, n. gen. and sp., is an unusual therian in having a "pseudo-talonid" basin on the lower molars anterior to the trigonid. Apparently an analogue of the protocone on the upper molars occluded in the pseudo-talonid and thus functionally it played a role similar to the talonid of tribosphenic therians. Being of medial to late Jurassic age, this "pseudo-tribosphenic" form predates the earliest known tribosphenic therian by at least 30 million years. With well developed accessory bones in the lower jaw, Shuotherium dongi was more primitive than any known tribosphenic therian. Perhaps it was a factor linked with the primitive nature of the jaw which explains why it was the tribosphenic and not the pseudo-tribosphenic molar pattern which was a key step in the radiation of the therians.