go north
Scientists working in northern Alaska have described a tiny fossil mammal that thrived in the planet’s coldest climates about 73 million years ago. The creature’s form resembled a modern shrew, known for quick, delicate movements.
The study, led by Jaelyn Eberle from the University of Colorado Boulder, documents this Late Cretaceous species in a brief report published in the Journal of Systematic Paleontology. The team named the species sikuomys micros, taking its name from the Iñupiaq word for ice and Greek roots meaning mouse and small.
The name mirrors what the animal likely looked like. Though nicknamed the little ice rat, it was not a rodent and was not a true mouse. It belonged to an extinct mammal family called Gypsonictopidae and stood out for its minute size, possibly smaller than a typical 11 gram specimen. Its appearance and tiny size suggest a creature that might have resembled a shrew and weighed roughly the mass of an empty soda can.
Fieldwork on the search for these fossils involved a demanding task. The new species was identified from only a handful of remains. Tiny teeth, each the size of a grain of sand, provided crucial clues to this elusive animal.
One of the recovered teeth is described as the size of a grain of sand, underscoring the minuscule nature of the find.
Expert researchers have noted their fascination with distant corners of the world. The scientists acknowledge that discoveries are often surprising and memorable, bringing new understanding to paleontological records.
These tiny fossils offer a fresh window into ancient Alaska, with implications for how Arctic ecosystems functioned 73 million years ago. The Arctic then hosted a forest alongside small mammals and birds, all adapting to a highly seasonal climate that included long polar nights, icy winters, and persistent cold conditions.
go north
Reaching the edge of the world required a remarkable effort. The team excavated sediments along the Colville River near the Beaufort Sea on Alaska’s north coast. Part of the Prince Creek Formation, the area is remote enough that exploration involved travel by snowmobile or small plane across roughly 75 miles from Deadhorse, Alaska.
Researchers describe a lost world where Arctic animals adapted to extreme seasonal changes. The Prince Creek site provides a natural case study for understanding the physiology and behavior of these animals under severe climate fluctuations.
Unlike some giants of the era, mammal fossils in this region are mostly teeth and jaw fragments. The team recovered many tiny specimens by washing and sorting soil from the riverbank under a microscope in the lab.
If he lived this far north, why was he so small?
The tiny teeth of sikuomys micros reveal a curious evolutionary pattern. In many mammal groups, larger sizes are common at higher latitudes and in cooler climates. Yet sikuomys micros and its close relatives appear to break this rule, with several related species living thousands of kilometers south and weighing three to five times more. This pattern hints at a growth strategy shaped by the Arctic environment.
Scientists propose that the ice rat’s very small size may reflect limited winter food supplies in Alaska. Small body size can reduce energy and food requirements, a notion echoed by comparisons to some modern mice.
One inference is that sikuomys micros could spend the cold season underground, a lifestyle that might have aided their survival after the dinosaurs’ mass extinction about 66 million years ago. Burrowing mammals often fare better during harsh periods when surface resources vanish amid climate shifts.