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Fossil fragments of the jawbones of a mouse-like creature found in Petrified Forest National Park in Arizona last year by a PhD from Virginia Tech College of Science. Candidates are indeed a recently discovered species of cynodont or mammalian stem of 220 million years, a precursor of modern mammals.
The discovery of this new species, Kataigidodon venetus, was published today in the journal Biology letters by lead author Ben Kligman, a doctoral student in the Department of Geosciences.
“This discovery sheds light on geography and the environment during early mammalian evolution,” Kligman said. “It also adds to the evidence that humid climates played an important role in the early evolution of mammals and their closest relatives. Kataigidodon lived alongside dinosauromorphs and possibly the first dinosaurs related to Coelophysis – a small bipedal predator – and Kataigidodon was probably prey on these early dinosaurs and other predators such as crocodiles, small quadrupedal coyote-like predators related to living crocodiles. “
Kligman added that finding a fossil that is part of Cynodontia, which includes close cousins of mammals, such as Kataigidodon, as well as true mammals, from Triassic rocks is an extremely rare occurrence in North America. Prior to Kligman’s discovery, the only other unmistakable late Triassic fossil of western North America was the 1990 discovery of an Adelobasileus cromptoni skull in Texas. Note that 220 million years ago, modern Arizona and Texas were located near the equator, near the center of the supercontinent Pangea. Kataigidodon allegedly lived in a lush tropical forest ecosystem.
Kligman made the discovery while working as a seasonal paleontologist at the Petrified Forest National Park in 2019. Kataigidodon’s two fossil lower jaws were found in the Upper Triassic Chinle Formation. Since only the lower jaws have been discovered and are quite small – half an inch, the size of an average grain of rice – Kligman has only a semi-square image of what the creature looked like, about 3.5 inches in total body size, minus the tail.
Along with the jaw fossils, Kligman found complex incisors, canines, and post-canines, similar to modern mammals. Given the pointed shape of its teeth and small body size, it likely ate a diet of insects, Kligman added. (Why are fossils of jaws commonly found, even among small specimens? According to Kligman, the fossil record is “biased” towards preserving only the largest and most robust bones in a skeleton. The other smaller or more fragile bones – ribs, arms , feet – disappear.)
Kligman did the fieldwork, sample preparation, CT scan, study conception and design, and manuscript writing. He added that he and his collaborators only discovered the fossils were of a new species after examining the jaw CT scan dataset and comparing it to other related species.
“It probably would have looked like a small rat or a mouse. If you saw it in person you would think it was a mammal,” Kligman added. Does he have fur? Kligman and the researchers he worked with to identify and name the creature don’t actually know. “Triassic cynodons were not found from geological environments that could preserve fur if it were there, but later the non-mammalian Jurassic cynodons had fur, so scientists assume the Triassic ones did too.”
The name Kataigidodon venetus derives from the Greek words for thunderstorm, “kataigidos” and tooth, “odon” and the Latin word for blue, “venetus”, all referring to the place of discovery of the Crest of the storm, and the blue color of the rocks in this site. Kligman did not name the creature, however. This task was entrusted to Hans Dieter-Sues, co-author and curator of vertebrate paleontology at the Smithsonian National Museum.
Other collaborators include Adam Marsh, the park’s paleontologist at Petrified Forest National Park, who found the jaw fossils with Kligman, and Christian Sidor, an associate professor in the University of Washington’s Department of Biology. The research was funded by the Petrified Forest Museum Association, Friends of Petrified Forest National Park and the Virginia Tech Department of Geosciences.
“This study exemplifies the idea that what we collect determines what we can say,” said Michelle Stocker, Kligman’s assistant professor of geosciences and doctoral consultant. “Our assumptions and interpretations of past life on Earth depend on the actual fossil materials we have, and if our research images to find fossils focus only on large-bodied animals, we will miss those important small specimens that are critical to understanding the diversification of many groups “.
Given that Kataigidodon is only the second other unambiguous Late Triassic cynodonto fossil found in western North America, could there be other new species out there waiting to be found?
Kligman most likely said. “We have preliminary evidence that multiple cynodont species are present at the same site in Kataigidodon, but we hope to find better fossils,” he added.
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