Arizona scientist discovers new species of ancient turtle at Mesa museum
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An ASU paleontologist working on a collection of fossils from the Zuni Basin in northwestern New Mexico has identified a previously unknown species of ancient turtle.
“Previous to this, there have been no terrestrial fossil turtles discovered in North America from this time period, so I knew it was probably going to be something unique,” said lead author Brent Adrian, a practicing paleontologists who is currently earning his doctorate at the university.
The paper appears in the journal Cretaceous Research.
The find, which dates back to a 12-million-year gap in the fossil record called the Turonian period, provides valuable clues about turtle evolution.
Despite what movies portray, real fossil discoveries mainly take place in labs — and in the holdings of places like the Arizona Museum of Natural History in Mesa. In this case, the subject was a collection of fossils gathered from the Zuni Basin in the late 1990s.
“It was the nicest specimen of fossils from that area and was relatively complete, and I recognized what kind of turtle it was because I had had worked on this group of turtles previously,” said Adrian.
“That kind of turtle” is a baenid, part of an extinct and diverse family of freshwater turtles endemic to North America.
Although the keratin that covers a turtle’s bony shell is not preserved in fossils, the bony part retains an image of the scale patterns. These are preserved as grooves showing where the seams, or sulci, once separated the scales.
It was there Adrian spotted a unique pattern.
“So I got to looking at it more closely and started looking in the literature and comparing it to what's known and realized that it had a combination of features which was unique,” said Adrian.
The team dubbed the Cretaceous turtle Edowa zuniensis, from the Zuni word for turtle (“Edowa”) and the Zuni Basin (“zuniensis”), where it was discovered.
E. zuniensis lived during one of the warmest periods of the Cretaceous around 90 million years ago. They dwelled near the Western Interior Seaway, an inland sea that once bisected North America.
The new species differs very little from relatives that flourished 15 million years later, which suggests advanced, successful traits developed in the turtles earlier than once thought.
Marks on the fossils suggest the turtle was food for leeches in its lifetime, and blunt, crushing tooth marks indicate it was attacked by a crocodile. Adrian said croc attacks were not only common, but that some species of crocodile evolved to eat turtles specifically.
“You're going to find some trace probably on most turtles of this of this type,” he said. “Sometimes it's very clear when you find them — the shell was bitten in half or something like that. The crocs at that time were pretty huge.”
