“O” is for Oxyclaenus
Oxyclaenus was a scansorial mammal. That means it lived in the trees, rather like squirrels do today. Its relationships to other mammalian groups is a matter of discussion right now, but it does seem to potentially be related to the Mesonychidae which may or may not be related to whales. (Probably not. I talk about this a bit with Dissacus.)
Most recently, Oxyclaenus has been included into a larger group of mammals called the ungulata, the hoofed mammals. Regardless, its relationships with other mammals are complex and can result in some hair-pulling.
Oxyclaenus is related to another important species (at least it’s put in the same family as, anyway) called Protungulatum. The species Protungulatum donnae made the presses a few months ago as the earliest known placental mammal. It was sufficiently interesting, that I posted about it myself in my regular Friday Headlines series.

The teeth of Protungulatum and of Oxyclaenus are of the simple tribosphenic design, best adapted to the eating of bugs.

Part of the A to Z Blogging Challenge
For 4-17-13