Vegetarian Hammerheads

We typically write about dinosaurs here. We then branched into mammals at different points. We sometimes even talked about birds, small reptiles, varied reptiles (turtles, snakes, etc.), and amphibians from time to time. We have discussed traditional looking animals (i.e. animals that we expect to look a certain way as in T. rex always looks kind of like we expect T. rex to look). We have also looked at very odd looking animals (Megacerops and Ceratosaurus, I'm thinking immediately of you). I think we ought to restart with an animal that is different looking and from one of the interesting fringe groups that we have discussed. To top things off, this somewhat recently described animal looks like pretty much none of its closest living relatives, making it far from what we might expect to see.

Enough intrigue and vagueness, we will start off this month by discussing Atopodentatus unicus. An herbivorous pantestudine (a group that includes the living turtles, testudines, and their ancestors the extinct "stem-turtles") marine reptile that has been assigned as a possible primitive (basal) member of the sauropterygia (the "lizard flipper" group that includes long and short-necked plesiosaurs). This classification follows the Schoch and Sues 2015 phylogeny that places sauropterygia within pantestudines (one can find other arrangements of the family tree that make this description hard to accept). Regardless, this animal appears to be related to turtles, but also has a long neck and long limbs with elongate digits that appear to be situated into primitive flippers. It also has a long tail and many ribs and gastralia ("belly ribs"). Despite all of these "normal" sounding bodily descriptions of a large marine reptile that make it sound like a very typical swimming air-breather of the Triassic, its head is anything but normal.

The name Atopodentatus translates to "Unusual toothed" and, with a "zipper-like" smile of teeth, it is unicus ("unique"). The anterior part of the skull can best be described as "hammerheaded", with the teeth forming their "zipper-like" pattern at the front of the mouth. The entire head is not hammer head shaped, only the mouth. This formation is very interesting. It looks almost like a hadrosaur ("duck-billed" dinosaur) mouth, but filled with small peg-like teeth. Approximately 8 million years older than any other herbivorous marine reptile, Atopodentatus is thought to have fed on algae embedded in the sea floor.