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 .
Castorocauda was a genus of small , semi-aquatic relative of mammals which lived in the Jurassic period , around 154 million years ago . Its fossil was found in lakebed sediments of the Daohugou Beds of Inner Mongolia .