This is still a work in progress. Almost finished, but not quite. But, since I'm not entirely sure when I'm going to get back to it, I've decided to upload the WIP for now.
Castorocauda lutrasimilis was a Middle to Late Jurassic mammaliaform - an almost mammal, but just not quite there yet. Its fossil is the oldest direct evidence of fur in synapsids.
It had a beaver-like tail, and a platypus-like venom spurs on its ankles, and it fed on fish like an otter.
Those three are just napping, getting some rest is important, even during the mesozoic.