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Fossils Show North America Was the Birthplace of Marsupials

A new fossil discovery in North Dakota proves that possum-sized marsupials roamed North America during the Cretaceous age and had what may have been the most powerful mammalian jaws in history. How powerful? These marsupials actually ate dinosaurs much larger than them. Wait a minute … marsupials in North America? That’s right, and this discovery may also prove that the original marsupials came from that continent.

What I love about Didelphodon vorax is that it crushes the classic mold of Mesozoic mammals. Instead of a shrew-like mammal meekly scurrying into the shadows of dinosaurs, this badger-sized mammal would’ve been a fearsome predator on the Late Cretaceous landscape—even for some dinosaurs.

While dinosaurs may not have loved it, Gregory P. Wilson does. The adjunct curator of vertebrate paleontology at the Burke Museum of Natural History and Culture and associate professor of biology at the University of Washington was the lead author of a new report in Nature Communications on the fossil find. The four fossils included a nearly-complete skull and two upper jaws of a marsupial ancestor known as the Didelphodon vorax – pieces never before found in previous discoveries.

D. Vorex fossils: partial snout (far-left), skull (second left), upper jaw bones (right).

D. vorax fossils: partial snout (far-left), skull (second left), upper jaw bones (right).

These new D. vorax bones show that they were the largest metatherians (marsupial ancestors) to live during the Cretaceous period – weighing from 5.3 to 11.5 lbs. (2.4 to 5.2 kg). Using a CT scan of the skull and jaw bones, they modeled the head and determined that D. vorax had the strongest bite of any mammal ever. Though small, their teeth and bite force indicated they could have killed and eaten small dinosaurs of the period.

Reconstruction of D. vorax skull

Reconstruction of D. vorax skull

As exciting as this news was, the researchers were stunned when they found these fossils in 66-to-69 million-year-old deposits in the Hell Creek Formation in Montana and North Dakota. That predates known metatherians, especially those from South America where it has been previously believed that they originated.

Closeup of D. vorax skull fossil

Closeup of D. vorax skull fossil

It appears now that there were five major lines of marsupial ancestors in North America 85-to-100 million years ago. They appeared to grow, flourish and further diversify right up until the Cretaceous–Palaeogene extinction event 66 million years ago, which seems to have pushed them to South America. Wilson describes the importance of new discoveries and research.

Our study highlights how, despite decades of paleontology research, new fossil discoveries and new ways of analyzing those fossils can still fundamentally impact how we view something as central to us as the evolution of our own clade, mammals.

Another excellent reason to keep promoting and expanding the teaching of science in schools.