Tiny Ice Mouse With Teeth As Big As a Grain of Sand Thrived Alongside Dinosaurs in the Frigid Ancient Arctic Alaska, Study Reveals

In northern Alaska, paleontologists have made a remarkable find - a minuscule fossilized mammal they call "ice mouse" that once thrived in what could have been one of the planet's chilliest environments approximately 73 million years ago.

The team recently detailed their discovery of this Late Cretaceous creature in a study, titled "A new tiny eutherian from the Late Cretaceous of Alaska," which is featured in the Journal of Systematic Palaeontology.

A Journey to Finding the Ice Mouse

Around 70 million years ago, during a frigid era in northern Alaska, dinosaurs roamed in perpetual winter darkness. This icy landscape, once situated above the Arctic Circle, appeared inhospitable to many creatures, but it provided a suitable habitat for a tiny mammal that resembled an Arctic shrew.

Dubbed "Sikuomys mikros," which translates to "ice mouse" (combining the Iñupiaq word "Siku" for ice and the Greek words "mys" and "mikros" for mouse and little), this miniature mammal, belonging to the extinct Gypsonictopidae family, weighed just 11 grams, equivalent to two nickels, and was approximately the size of a modern shrew.

The Prince Creek Formation (PCF) in northern Alaska is a treasure trove of dinosaur fossils, including 13 distinct species, some closely related to renowned dinosaurs like T.rex and Triceratops.

Jaelyn Eberle, a geological sciences professor at the University of Colorado, Boulder, specializes in studying the warm-blooded creatures that coexisted with these massive dinosaurs in the ancient Arctic landscape. The stark contrast between these colossal dinosaurs and the diminutive ice mouse is intriguing. S. mikros was significantly smaller than an average house mouse.

Paleontologists exploring the PCF employ a meticulous approach to their findings. They carefully collect the sediment surrounding dinosaur fossils, followed by a thorough washing process to remove tiny dirt particles.

Super-fine mesh prevents larger objects from escaping, and the remaining debris is examined under a microscope. This technique unveils minute details that would be impossible to discern in the field, such as millimeter-sized teeth.

While this sediment analysis reveals various mammal bones, identifying the animals can be challenging, particularly when they lack a complete skeleton. Teeth hold immense value in paleontology since they often offer diagnostic insights about species.

In the case of S. mikros, distinct tooth features led researchers to categorize it as a new species. This discovery illuminates the fascinating and diverse ecosystem that thrived alongside the dinosaurs in ancient Arctic Alaska.

Ice Mouse Could Have Not Hibernated

The scarcity of a skull and other bones makes it challenging to glean extensive insights into S. mikros. However, by drawing comparisons with how related species live, researchers like Eberle can make educated inferences. S. mikros likely did not hibernate, as modern shrews and voles exhibit similar behavior.

They probably overwintered by staying awake and continuously feeding throughout the year, possibly hiding under leaf litter or underground. Their diet likely consisted of insects and other invertebrates like worms.

Interestingly, the paper highlights a deviation from the typical pattern observed in modern mammals. Generally, larger mammals tend to inhabit higher latitudes in colder climates, where they can store fat to endure harsh winters with limited food.

However, S. mikros does not conform to this trend. Some of its relatives lived further south and were considerably larger, with sizes three to five times that of the tiny Alaskan creature. This suggests that the ice mouse's diminutive size was an evolutionary adaptation, as smaller animals require less food to sustain themselves during the winter months.

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