Archosaur
Late Jurassic (Tithonian)
Morrison Formation
Bone Cabin Quarry, Albany County, Wyoming, USA

4mm Tooth.

Isolated teeth of many animals such as small reptiles can be difficult to identify to genus or family because a lot of tiny teeth are roughly the same shape without the surface area for distinctive characters that larger teeth can bear.  This one was collected at the legendary Bone Cabin Quarry.

Yeah, we don’t know what it is so it’s cheap.