Symmetrodonta is a traditionally paraphyletic group of Mesozoic mammals and mammal-like synapsids, ranging from the latest Triassic to Late Cretaceous. The molars have a triangular aspect when viewed from above and there is no well-developed talonid. 'Symmetrodonts' are generally rare and poorly represented in the fossil record. Most research during the 21st century has concluded that they do not represent a discrete phylogenetic category. however, the name is still used informally by some researchers for convenience, or restricted to the Spalacotheriids and Zhangheotheriids.
The Spalacotheriidae has acute−angled molariform teeth, strongly reduced talonids, and conspicuous anterior and posterior cingulids.
Spalacotheridium noblei was one of the smallest known mammals; each molar was little more than 0.25 mm across.