Castorocauda

Castorocauda is a genus of small, semi-aquatic mammal relatives living in the Jurassic period, around 164 million years ago, found in lakebed sediments of the Daohugou Beds of Inner Mongolia. It contains the single species Castorocauda lutrasimilis. They were highly specialized, with adaptations evolved convergently with those of modern semi-aquatic mammals such as beavers, otters, and the platypus.

Classification

Castorocauda lutrasimilis is a member of the order Docodonta, which is a wholly extinct group of Mammaliaformes. It is not considered to be a mammal by the crown group definition, which takes the mammals to be the group containing the most recent common ancestor of all living mammals (the monotremes, placentals, and marsupials) and its descendants. Many writers, however, do not define Mammalia as a crown group; Kielan-Jaworowska et al. (2004), for example, defines Mammalia as the group originating with the last common ancestor of Sinoconodon and living mammals, a definition that includes Docodonta.