Ok, so there was no cheese in mesozoic, but like that's going to stop a determined stem-mammal.
I'm really happy with this model, and I have two pieces with it that I'm still working on.

Castorocauda lutrasimilis was a Middle to Late Jurassic mammaliaform (so, not yet a mammal, but very close) from what is now China. It was semi-aquatic, fed on fish and other small critters, had a beaver-like tail and platypus-like venom spurs on its ankles. It's also the oldest direct evidence of fur in synapsids, so it was most definitely fluffy.