Post by Curator Dr. Andrew T. McDonald
Two weeks ago, Western Science Center's social media presented a large and rather complete 80-million-year-old turtle shell from the Menefee Formation in New Mexico. We've been making good progress on prepping that turtle and will have more to say about it soon. For today, I wanted to surprise you all with something that surprised us last week. WSC fossil prep volunteer Joe Reavis and I were sorting through bone fragments that will reattach to the turtle shell when we noticed a flat disk of bone that didn't seem to attach to anything else and with a surface showing a number of small pits (bottom row, second from right in the image). It was pretty clear that this was not part of the turtle, and that it was actually an osteoderm, a small bone that would have been set in the skin of some type of armored animal.
In the Menefee Formation, we know of two types of animals that bore osteoderms - crocodilians and the armored herbivorous dinosaur Invictarx, which we and our colleagues at Zuni Dinosaur Institute for Geosciences named in 2018. We have osteoderms from at least two different Menefee crocodilians here at WSC: an alligator-sized species and the gigantic Deinosuchus. In both of these crocodilians, the osteoderms are covered in large, deep pits, as you can see in this image of an osteoderm at WSC. In contrast, the osteoderm from the turtle site has very small pits.
Joe and I found some additional pieces that show the same texture as the disk-shaped osteoderm. I compared them to osteoderms from the three specimens of Invictarx, and they're a good match, showing similar overall shapes and patterns of small pits. So, among the many pieces of turtle shell we collected at the site are some osteoderms of a fourth Invictarx! It's not rare to find more than one type of animal at a single site in the Menefee Formation; we have several sites that have produced pieces of dinosaur bone, crocodilian osteoderms, turtle shell bits, fish scales, and freshwater snails in an area of just a few square meters.
This material was collected by staff and volunteers from Western Science Center, Zuni Dinosaur Institute for Geosciences, and Southwest Paleontological Society.