Furry Fossil

Pharyngula: Jurassic beaver

One-sixty million years ago,
We see from prints, and tooth and bone,
The oldest furry mammal known
Would dive for piscine treats below.
Castoro: beaver; cauda: tail;
Lutra: otter; similis: like.
Guard hairs, fur, an ankle spike,
Bones a creature's traits unveil.
Scales on tail, an otter's spine,
Seal-like teeth and swimmer's limbs;
Another one of nature's whims
That filled a niche before decline.
Hints and traces, clues that thrill us:
Castorocauda lutrasimilis.