Ice Mouse Rodent with Sand-Grain Teeth Thrived in Dinosaur Era Arctic

ice mouse rodent with sand grain teeth thrived in dinosaur era arctic.jpg Science

In the frozen landscapes of prehistoric Alaska, where dinosaurs once roamed and the frigid darkness of the Arctic Circle loomed for months on end, a tiny creature made its home. The Sikuomys mikros, or "ice mouse," a shrew-like mammal weighing a mere 11 grams — the equivalent of two nickels — and a few inches in length, thrived in this harsh environment teeming with dinosaurs. Bearing teeth the size of mustard seeds, these minuscule mammals have left behind fossils that are easily overlooked, yet they offer a fascinating glimpse into the diverse ecosystem of the Prince Creek Formation (PCF) over 70 million years ago.

The PCF is a treasure trove of dinosaur fossils, with scientists having discovered 13 different species, including relatives of the T.rex and Triceratops. Yet, amidst these colossal creatures, the microscopic teeth of the ice mouse have caught the attention of Jaelyn Eberle, a professor of geological sciences at the University of Colorado, Boulder. Eberle and her team have been studying these warm-blooded animals that managed to coexist with the dinosaurs, their findings recently published in the Journal of Systematic Palaeontology. Despite their diminutive size, these creatures present a captivating paradox to the typical patterns of evolution in harsh climates, shedding new light on how mammals have adapted to survive in inhospitable environments.

Tiny Shrew-Like Creature Lived Among Dinosaurs in Arctic Alaska

New research has unearthed insights into a miniature mammal that coexisted with dinosaurs in the harsh Alaskan winters over 70 million years ago. The creature, known as Sikuomys mikros or "ice mouse," managed to thrive in the constant darkness and freezing temperatures of the ancient Arctic landscape.

An Unlikely Survivor

The Sikuomys mikros, a shrew-like creature, was small in stature but big in survival. With a body length of just a few inches and a weight of around 11 grams, this tiny mammal managed to cohabit with a plethora of dinosaur species, including T.rex and Triceratops. The environment in which it lived, the Prince Creek Formation (PCF), is now a rich source of dinosaur fossils.

Jaelyn Eberle, a professor of geological sciences at the University of Colorado, Boulder, focuses on studying these warm-blooded micro-mammals that scurried among the colossal dinosaurs. Eberle and her team published their findings on the S. mikros in the Journal of Systematic Palaeontology. The team identified the creature based on its teeth, which measure a mere 1 to 1.5 millimeters.

The Art of Finding Mustard Seed-Sized Teeth

The paleontologists’ approach to finding these tiny fossils involved sifting through sediment collected from around dinosaur fossils found at the PCF. The sediment was sieved to filter out tiny dirt particles while retaining larger objects. This meticulous process enabled the team to discover over a dozen teeth from three separate sites.

Eberle explained that teeth are the most diagnostic fossils for mammals, stating that the S. mikros’ teeth were significantly different from its near relatives, suggesting it to be a new species. The team then estimated the animal’s size based on its tiny teeth.

What Small Size Tells Us

While the absence of a skull and other bones makes it challenging to determine much about the S. mikros, Eberle suggested that the creature’s small stature could provide clues about its survival strategy. She proposed that the S. mikros may not have hibernated but remained active throughout the winter, feeding on insects and other invertebrates.

The paper challenges the conventional wisdom that larger body mass is advantageous in colder climates, where animals can store fat to survive food scarcity during winter months. Eberle noted that the S. mikros’ relatives, which lived further south, were three to five times larger than this small Alaskan creature.


The discovery of the S. mikros provides fascinating insights into how tiny mammals could coexist with dinosaurs in extreme climates. It also challenges conventional thinking about body size and survival in harsh climates. The survival of these tiny creatures in the Arctic wilderness demonstrates the remarkable adaptability of life and offers new perspectives on how different species may respond to environmental challenges.

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