A new genus and species of eutherian mammal has been described from a handful of tiny teeth found in the Prince Creek Formation in northern Alaska, the United States. The species represents the northernmost occurrence of a Mesozoic eutherian (paleolatitude 80-85 °N).
Reconstruction of the Prince Creek Formation fauna. Image credit: Andrey Atuchin.
The newly-described species, Sikuomys mikros, lived in what is now Alaska during the Late Cretaceous epoch, some 73 million years ago.
The ancient mammal belonged to a family of now-extinct mammals called Gypsonictopidae.
Dubbed the ice mouse, Sikuomys mikros may have looked a bit like a modern-day shrew and weighed an estimated 11 grams.
The animal did not hibernate, but rather was active year-round, akin to living shrews.
“These guys probably didn’t hibernate,” said University of Colorado Boulder paleontologist Jaelyn Eberle.
“They stayed active all year long, burrowing under leaf litter or underground and feeding on whatever they could sink their teeth into, probably insects and worms.”
The tiny teeth of Sikuomys mikros, each about the size of a grain of sand, were collected from the Prince Creek Formation in northern Alaska.
“Those minute fossils are giving researchers a new window into ancient Alaska,” said Dr. Patrick Druckenmiller, director of the University of Alaska Museum of the North.
“Seventy-three million years ago, northern Alaska was home to an ecosystem unlike any on Earth today.”
“It was a polar forest teeming with dinosaurs, small mammals and birds.”
“These animals were adapted to exist in a highly seasonal climate that included freezing winter conditions, likely snow and up to four months of complete winter darkness.”
“Our team is revealing a ‘Lost world’ of Arctic-adapted animals,” said Dr. Gregory Erickson, a paleontologist at Florida State University.
“Prince Creek serves as a natural test of these animal’s physiology and behavior in the face of drastic seasonal climatic fluctuations.”
For many groups of mammals on Earth, species tend to get bigger at higher latitudes and cooler climates.
Sikuomys mikros and its close cousins seem to follow the opposite pattern.
“The ice mouse was so small because there was so little to eat during the winter in Alaska,” Professor Eberle said.
“We see something similar in shrews today. The idea is that if you’re really small, you have lower food and energy needs.”
“Sikuomys mikros may have spent the cold months in Alaska underground.”
“In the end, such a subterranean lifestyle may have been a blessing for animals like the ice mouse.”
“Burrowing mammals may have stood a better chance of surviving the harsh conditions that followed the meteorite crash that killed the dinosaurs 66 million years ago.”
The discovery is described in a paper published this month in the Journal of Systematic Palaeontology.
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Jaelyn J. Eberle et al. 2023. A new tiny eutherian from the Late Cretaceous of Alaska. Journal of Systematic Palaeontology 21 (1); doi: 10.1080/14772019.2023.2232359
