In the icy terrain of northern Alaska, a thrilling discovery has been made that takes us back to the chilling conditions of Earth around 73 million years ago. A minute fossil mammal, fittingly named Sikuomys mikros or “ice mouse,” provides fascinating insights into life in the Late Cretaceous period.

Led by Jaelyn Eberle at the University of Colorado Boulder, a team of paleontologists unveiled this discovery in the recent publication of the Journal of Systematic Palaeontology. The name Sikuomys mikros draws from the Iñupiaq word for “ice” and the Greek words for “mouse” and “little.”

Although the term “ice mouse” suggests a resemblance to modern mice, this small mammal, weighing less than an empty aluminum soda can, belonged to the now-extinct Gypsonictopidae family. Resembling a contemporary shrew, this tiny creature endured the harsh Arctic environment of ancient Alaska, where winter darkness lasted up to four months, and temperatures often dropped below freezing.

Remarkably, Eberle believes that this furry critter remained active year-round, feeding on insects and worms by burrowing underground.

A team of paleontologists digs in northern Alaska. Credit: Kevin May

The arduous task of discovering the fossil was equally fascinating. The new species was identified from a handful of teeth, each roughly the size of a grain of sand. Eberle commented on the excitement of working in remote places, stating, “You never know what you’re going to find, but you know it’s going to be new.”

These minute fossils have opened a fresh perspective into ancient Alaska. Patrick Druckenmiller, a study co-author, described northern Alaska of that time as “a polar forest teeming with dinosaurs, small mammals, and birds,” all adapted to extreme seasonal climates.


Unearthing Mysteries of the North
The discovery process itself was no small feat. Researchers, including paleontologists from the University of Alaska Fairbanks and Florida State University, unearthed the fossils near Alaska’s northern coast. The isolation of the site required travel by snowmobile or bush plane.

“Our team’s research is revealing a ‘Lost world’ of Arctic-adapted animals,” said Gregory Erickson, another co-author. “Prince Creek serves as a natural test of these animal’s physiology and behavior in drastic seasonal climatic fluctuations.”

These mammals’ fragile fossils provide a stark contrast to the large bones left by the region’s dinosaurs. The collection process involved sifting through buckets of dirt, washing away mud, and carefully sorting under a microscope.

A Peculiar Survival Strategy
The ice mouse’s survival offers a unique twist in understanding mammalian evolution. Unlike other species that grow larger in cooler climates, Sikuomys mikros and its kin followed the opposite pattern, with related species further south being much larger.

The lack of food during Alaskan winters may have contributed to the ice mouse’s small size, a survival strategy that allowed the creature to endure the frigid environment. Eberle compares this to modern shrews, explaining that smaller size correlates with lower food and energy needs.

It’s possible that Sikuomys mikros hibernated underground during the cold Alaskan months, a lifestyle that may have been a saving grace in the harsh aftermath of the meteorite crash that led to the extinction of the dinosaurs 66 million years ago.

This discovery of the so-called ice mouse opens a window into the living conditions of small mammals during the dinosaur era. It offers a unique look at survival strategies during extreme weather conditions, showing us how this tiny creature adapted to life in ancient Arctic Alaska. The ice mouse’s survival presents an intriguing aspect of prehistoric life and adds to the continually unfolding story of our planet’s history.


Cite for original article:

  1. Jaelyn J. Eberle, William A. Clemens, Gregory M. Erickson & Patrick S. Druckenmiller (2023) A new tiny eutherian from the Late Cretaceous of Alaska, Journal of Systematic Palaeontology, 21:1, DOI: 10.1080/14772019.2023.2232359


Paper: here

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