Marsupial lived among the dinosaurs of the Arctic

The animal of thumb size, named Unnuakomys hutchisoni, lived in the Arctic about 69 million years ago, at the end of the Cretaceous. His discovery, led by scientists from the University of Colorado and Alaska Fairbanks, is described in an article published in the Journal of Systematic Palaeontology.

The discovery adds to the image of an environment that, according to scientists, was surprisingly diverse. The tiny animal, the northernmost marsupial ever discovered, lived among a unique variety of dinosaurs, plants and other animals.

North Slope of Alaska, which was about 80 degrees north latitude when U hutchisoni lived there, once thought to be a sterile environment at the end of the Cretaceous. This perception has gradually changed since the discovery of dinosaurs along the Colville River in the 1980s, new evidence that the area was home to a diverse collection of unique species that did not exist elsewhere.

Finding a new marsupial species in the Far North adds a new layer to this evolving vision, said Patrick Druckenmiller, director of the North Museum of the University of Alaska.

"The north of Alaska was not only inhabited by a wide variety of dinosaurs, but we are actually discovering new species of mammals that have helped to complete the ecology," said Druckenmiller, who has been studying dinosaurs in the region for over a decade. "With each new species, we paint a new picture of this ancient polar landscape."

Marsupials are a type of mammal that carries undeveloped offspring in a pocket. Kangaroos and koalas are the most popular modern marsupials. The former parents were much smaller in late Cretaceous, said Druckenmiller. Unnuakomys hutchisoni Probably more like a tiny opossum, feeding on insects and plants while surviving in darkness for up to four months per winter.

The research team, whose project was funded by a grant from the National Science Foundation, has identified the new marsupial using a tedious process. With the help of many undergraduate and graduate students, they collected, washed and filtered old river sediments collected on the North Slope and then carefully inspected them under the microscope. For many years, they have been able to locate many fossilized teeth about the size of a grain of sand.

"I liken this to looking for proverbial needles in haystacks – more rocks than fossils," said Florida State University paleobiologist Gregory Erickson, who contributed to the newspaper.

Jaelyn Eberle, curator of fossil vertebrates at the Natural History Museum of the University of Colorado, led the effort to examine these teeth and some tiny jaws. Their analysis revealed a new species and kind of marsupial.

Mammalian teeth have unique cusps that differ from one species to another, making them a little fingerprint of dead bodies long ago, said Eberle, the lead author of the study.

"If I were to go down to the Denver Zoo to open the mouth of a lion and watch – which I do not recommend – I could tell you his gender and probably his species based solely on his teeth," Eberle says.

The name Unnuakomys hutchisoni combines the word Iñupiaq for "night" and the Greek word "mys" for mice, a reference to the dark winters of the animal and a tribute to J. Howard Hutchison, a paleontologist who discovered the fossil-rich site where his teeth were finally found.

Other co-authors of the Journal of Systematic Palaeontology The paper includes William Clemens, from the University of California at Berkeley; Paul McCarthy, UAF; and Anthony Fiorillo, from the Perot Museum of Nature and Science.