164 million year old beaver

The latest entry in the early mammalian diversity parade is Castorocauda lutrasimilis—which, translated from Latin, means "beaver-tailed creature that looks like an otter." The 50-centimeter-long creature, about the size of a modern-day platypus, lived about 164 million years ago in what is now northeastern China. It belongs to a group of animals called mammaliaforms, a dead-end lineage that branched off near the base of the mammal family tree, says Zhe-Xi Luo, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh.