A remarkable 94-million-year-old fossil found in South America is shedding new light on the ancient history of mammals.
The specimen, dubbed Cronopio dentiacutus, is one of the very few mammal fossils to come out of South America from the era when dinosaurs ruled the Earth.
The mouse-sized creature had a long snout, dagger-like canines and a powerful set of muscles it used to chew its insect food.
The mammal is a dryolestoid, an extinct group of animals distantly related to today´s marsupials and placentals.
“The new dryolestoid, Cronopio, is without a doubt one of the most unusual mammals that I have seen, extinct or living,” said John Wible, curator of mammals at the Carnegie Museum of Natural History.
University of Louisville paleontologist Guillermo Rougier and his team found the fossil, which breaks a roughly 60-million-year gap in what is known about South American mammals and their evolution.
“It looks somewhat like Scrat, the saber-toothed squirrel from ℠Ice Age,´ ” said Rougier, professor of anatomy and neurobiology at University of Louisville.
But even before they knew what it might look like, the researchers realized the importance of the discovery when they found the two fossilized skulls in 2006.
The skulls were embedded in rock in a remote area of northern Patagonia, about 100 miles from the city of Allen in the Argentinian province of Rio Negro. It took several years of patient lab work to remove the specimens from the rocks.
“We knew it was important, based on the age of the rocks and because we found skulls,” Rougier said.
“Usually we find teeth or bone fragments of this age. Most of what we know of early mammals has been determined through teeth because enamel is the hardest substance in our bodies and survives well the passage of time; it is usually what we have left to study.”
“The skull, however, provides us with features of the biology of the animal, making it possible for us to determine this is the first of its kind dating to the early Late Cretaceous period in South America.”
“This time period in South America was somewhat of a blank slate to us. Now we have a mammal as a starting point for further study of the lineage of all mammals, humans included.”
The prospects for further investigation on the southern continents are exciting.
“Until now, all we have had are isolated teeth and a few jaw fragments “¦ which don’t really help much in deciphering broader relationships,” said Rich Cifelli, presidential professor of zoology at the University of Oklahoma and a researcher.
“The new fossils provide a sort of Rosetta Stone for understanding the genealogy of early South American mammals, and how they fit in with those known from northern landmasses,” said Cifelli, who has spent his career discovering and identifying mammal remains.
“Now,” he said, “the burden is on the rest of us to find similarly well preserved fossils from elsewhere, so that the broader significance of Rougier´s finds can be fully placed in context.”
The study was published online November 2 in the journal Nature.
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Image Caption: Artist impression of Cronopio dentiacutus. Credit: Jorge Gonzalez/Guillermo Rougier
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