细齿兽类（Miacidae）是古新世至始新世（约3300-6500万年前）的原始肉食性动物。细齿兽类演化至现今肉食性的哺乳动物。

细齿兽类是细小像貂鼠的动物，身体及尾巴都很长。一些物种是栖息树上的，其他的则生活在陆地。牠们可能吃无脊椎动物、蜥蜴、鸟类及细小的哺乳动物，如鼩鼱科及负鼠目等。牠们的牙齿及头颅骨比现今的食肉目较少发育。牠们有裂齿，但没有成骨的鼓泡。牠们像Cimolestes，故食肉目有可能是从与有蹄动物有关的食虫动物演化而来。

细齿兽类可以分为两类：有完整臼齿的miacine及有专门裂齿的viverravine。

Miacids are extinct primitive carnivoramorphans within the family Miacidae that lived during the Paleocene and Eocene epochs, about 62–33 million years ago. Miacids existed for approximately 29 million years.

Miacids are thought to have evolved into the modern carnivorous mammals of the order Carnivora. They were small carnivores, superficially marten-like or civet-like with long, little bodies and long tails. Some species were arboreal, while others lived on the ground.