Tiny dino-era “night mouse” found above the arctic circle

<em>Unnuakomys hutchisoni</em> iis is almost undetectable in the mural is that the Arctic landscape from the late Cretaceous.
(James Havens)

A small marsupial relative who lived in the twilight of the dinosaurs, as well as in a literal twilight for a large part of the year, is discovered in the Arctic.

The mouse-sized creature lived 69 million years ago in the northern most part of the day, on the equivalent width of the northern islands of the Svalbard archipelago today. The high latitude would be in total darkness for four months a year.

Scientists found the tiny teeth and jawbone of the animal on the side of a steep bank of a river in Alaska. She called the animal Unnuakomys hutchisoni to reflect are often unlit home range: In the native Inupiaq language, unnuak, pronounced as Oo-noo-ah, meaning “night”. Mys is Greek for “mouse”. [See Photos of the north Pole at Night Mouse’]

“We don’t think about finding small marsupials at 85 degrees north latitude,” said Jaelyn Eberle, curator of vertebrate palaeontology at the University of Colorado, Boulder, Museum of Natural History and one of the discoverers of the new species.

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Alaskan excavation

The teeth and bones of the “night of the mouse,” are popping out of the soil, occasionally in the tens of years of excavations along the Colville River in the Northern Slope of Alaska. It is an unusual place for excavations: Paleontologists have to wear hardhats while in balance on the steep banks, because the banks periodically crumble and slough dirt and rock in the river. The sound of these mini-avalanches is heard from the tents on the sand banks where the researchers camp each night, Eberle said.

Paleontologist Patrick Druckenmiller of the University of Alaska, Fairbanks, and colleagues are dinosaurs digging up the banks for a year. After a period of time, Druckenmiller told the Science, the team has learned how to recognize the thin sediment layers, less than 4 inches (10 centimeters) thick, which are deposited at the base of small Chalk streams. These layers have the tendency to keep small, rare fossils, such as mammal teeth and fish bones. [In Images: The Oldest Fossils on Earth]

Once the researchers find the particular layers, Druckenmiller said, they scoop them from the wholesaler in buckets. The clay and dirt are then washed, and the paleontologists, together with their students and assistants, sifting through buckets upon buckets of the remaining thick pellets under microscopes.

The majority of the mammalian teeth, Eberle said, max of about 0.06 inch (1.5 millimeters) in length. Until now, though, Eberle, and other researchers from various universities involved in the project have found about 70 U. hutchisoni teeth and a lower jawbone.

Small and toothy

That is enough to make an estimate of the size of the animal and council to her diet. The animal was part of a group called Metatheria, Eberle said, including the current marsupials . It weighed about an ounce, about the size of a mouse or a small shrew, and his sharp teeth suggest that it may have feasted on insects. Judging by the teeth, the researchers suspect U. hutchisoni perhaps a bit like modern possums.

U. hutchisoni is the most northern of the relatives in the family Pediomyidae, Eberle said. Previously, the most northern place where this family of mammals discovered in the north of Alberta, Canada. Today, the excavation is approximately 70 degrees north latitude. In the Cretaceous period , given the movement of the continents, it would have been between 80 and 85 degrees, which means that the “night of the mouse” would have about 120 days per year 24 hours per day dark.

The climate 69 million years ago, it was a bit warmer than today, so the habitat would have an average of about 43 degrees Fahrenheit (6 degrees Celsius). It would be below freezing in the winter, Eberle said, and cool in the summer. U. hutchisoni would have lived in underground caves as an adaptation to the cold weather, ” she said. It would have scampered in the midst of pine forests, inhabited by duck-billed dinosaurs and smaller meat-eating relatives of the Tyrannosaurus rex .

The larger research project, funded by the National Science Foundation, is dedicated to the unraveling of this old Arctic habitat, Druckenmiller said. So far, he said, both the mammals and dinosaurs found in the north of Alaska appear to represent unique species not found further to the south.

“That is a pretty cool discovery, to know that we have in principle a distinctive polar fauna during the era of the dinosaurs,” he said.

The newly discovered species of mammals not outlast the dinosaurs, as some of the other small mammals of the Cretaceous did. Other mammals in the sediments of the groups that have survived, Eberle said, all the fossils have yet to be fully analysed.

“The people have the hypothesis that the small and the ability to potentially hide underground if a big asteroid comes along would have preadapted these guys to survive,” she said.

The research is published Feb. 14 in the Journal of Systematic Paleontology.

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Originally published on Live Science.

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