Fossil Discovery Confirms Mammals' Original Ancestors

Reconstruction of a new mammal species, Xianshou songae. This mouse-sized animal was a tree dweller in the Jurassic forests. (Credit: Zhao Chuang) What looks like a rat, climbs trees and has a tail like a lemur? It’s your cousin, of course! Before you take offense to that statement, please note that we’re referring to Xianshou songae, one of three newly discovered, extinct species that lived roughly 160 million years ago. This trio of species, unearthed in China, helps settle a long debate regarding the origin and earliest evolution of mammals. So by your cousin, we mean the earliest relatives of all mammals.