“X” is for Xanclomys
Xanclomys is a multituberculate with a uniquely shaped lower fourth premolar.
Alas, Xanclomys is a rare little mammal, so there’s little information about it. The unique shape of its premolar did make me want to compare it with my new species Fractinus when I was trying to convince myself that I really did have a new species.
Two things of note with the lower fourth premolar of Xanclomys. 1) The tooth is delta-shaped, with a rear-pointing peak. 2) The serrations (the ridges going down the side of the teeth) are not perfectly straight. They have a wave in them. Such features are not observed in any other multituberculate species.
Part of the Blogging from A to Z challenge