Found: 220 Million-Year-Old Rat-Like Fossil, Precursor of Modern Mammals

A Photoshop-created image of how Kataigidodon venetus may have looked, illustrated by Ben Kligman, a doctoral student in the Department of Geosciences and Hannah R. Kligman. (Credit: Virginia Tech)

(CN) — Scientists on Tuesday announced the discovery of a distant ancestor of modern mammals, a 220-million-year-old rat-like creature found in the Petrified Forest National Park in Arizona.

The newly discovered species Kataigidodon venetus is detailed in a study published in the journal Biology Letters by a research team from Virginia Tech’s College of Science.

“This discovery sheds light on the geography and environment during the early evolution of mammals,” said lead author Ben Kligman, a doctoral student, in a statement. “It also adds to evidence that humid climates played an important role in the early evolution of mammals and their closest relatives.”

Kligman said the Kataigidodon lived at the same time as early dinosaurs known as dinosauromorphs and were possibly hunted by them. The fossils, discovered last year, represent a significant finding as the only other cynodont, or early mammal, fossil from the late Triassic Period found in western North America was discovered 30 years ago in Texas.

The researchers said, “220 million years ago, modern-day Arizona and Texas were located close to the equator, near the center of the supercontinent Pangaea. Kataigidodon would have been living in a lush tropical forest ecosystem.”

We have an incomplete picture of what the creature looked like because Kligman only discovered fossils of the two lower jaws, each only half an inch in size, and teeth. But the scientists estimate it to be about 3.5 inches in length, not accounting for the tail. The mammal ancestor likely fed on insects, Kligman said, due to its pointed teeth and small body.

“It likely would have looked like a small rat or mouse. If you were to see it in person you would think it is a mammal,” Kligman said, adding that researchers are unsure if it had fur. “Triassic cynodonts have not been found from geological settings which could preserve fur if it was there, but later nonmammalian cynodonts from the Jurassic had fur, so scientists assume that Triassic ones did also.”

Scientists named the creature Kataigidodon venetus after the discovery site Thunderstorm Ridge, using the Greek words thunderstorm, “kataigidos,” and tooth, “odon.” The term “venetus” is Latin for blue and comes from the blue rocks found there.

“This study exemplifies the idea that what we collect determines what we can say,” said Michelle Stocker, assistant professor of geosciences and Kligman’s doctoral adviser. “Our hypotheses and interpretations of past life on Earth depend on the actual fossil materials that we have, and if our search images for finding fossils only focuses on large-bodied animals, we will miss those important small specimens that are key for understanding the diversification of many groups.”

Kligman said researchers are hoping to find more fossils of the creature and foster a better understanding of how it lived hundreds of millions of years ago.

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