Scientists in Alaska discover fossil of tiny ‘ice mouse’ that lived 73 million years ago

Scientists have discovered a tiny fossil mammal in Alaska that may have survived about 73 million years ago in one of the coldest conditions ever endured by living organisms on Earth.

The mammal is being described as an “ice mouse” by researchers at the University of Colorado Boulder in a study published in the Journal of Systematic Palaeontology.

Fossil given name ‘Sikuomys mikros’

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The scientists have given the fossil a fitting name—Sikuomys mikros—from "Siku," an Iñupiaq word for "ice," and "mys" and "mikros," the Greek words for "mouse" and "little."

Simply put, experts have likened the fossil to a tiny mouse, who might have appeared like a modern-day shrew.

They weighed an estimated 11gmor even less. However, the study has clarified the mammal was actually not a mouse but hailed from a now-extinct family different altogether—Gypsonictopidae.

The ice mouse might have endured straight four months of unending darkness even as temperatures fell way below the freezing point.

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Eberle, curator of fossil vertebrates at the CU Museum of Natural History and professor in the Department of Geological Sciences, anticipated that "these guys probably didn't hibernate."

“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," she observed.

Why the discovery of the fossil is significant?

The find is significant as it is always difficult to spot mammal fossils of this tiny size. Some species have been identified only from a handful of tiny teeth, some even smaller than a grain of sand.

In Eberle’s words, “I always like working at the ends of the Earth. You never know what you're going to find, but you know it's going to be new."

Little mice challenging conventional beliefs

Many groups of Earth's mammals tend to become larger as they move towards higher latitudes and cooler climates. However, the ice mouse and its relatives defy this trend.

Researchers have discovered related species living thousands of miles to the south that were three to five times larger than the tiny Sikuomys mikros.

Eberle suggests that the small size of the ice mouse could be attributed to the scarcity of food during Alaskan winters.

This phenomenon is also observed in present-day shrews, where being small helps to reduce food and energy requirements.

It's possible that Sikuomys mikros spent the colder months underground in Alaska. This subterranean lifestyle might have provided a significant advantage to creatures like the ice mouse.

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