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Greg Wilson & collaborators on marsupial origins in N. America

Thursday, December 8, 2016 - 14:30

Move over, hyenas and saber-toothed cats; there’s a mammal with an even stronger bite. A new study by paleontologists at the Burke Museum of Natural History & Culture and the University of Washington describes an early marsupial relative called Didelphodon vorax that lived alongside dinosaurs and had, pound-for-pound, the strongest bite force of any mammal ever recorded.

Published in the journal Nature Communicationsthe team’s findings suggest mammals were more varied during the age of dinosaurs than previously believed. Didelphodon was able to eat a variety of foods and was likely a scavenger-predator who could eat prey ranging from snails to small dinosaurs.

In addition, the team re-traced the origins of marsupials. Previous theories attribute South America as the origin of marsupials, but anatomical features of the Didelphodon point to marsupials originating in North America 10 to 20 million years earlier than originally thought and later dispersing and diversifying in South America.

A scientist holding a skull


Greg Wilson holding a fossilized Didelphodon skull.Burke Museum of Natural History & Culture

“What I love about Didelphodon vorax is that it crushes the classic mold of Mesozoic mammals,” Greg Wilson, Burke Museum adjunct curator of vertebrate paleontology and UW associate professor of biology. “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.”

All of these findings are made possible by four fossil specimens recently discovered in the 66 to 69 million-year-old deposits of the Hell Creek Formation in Montana and North Dakota. Prior to these discoveries, the 60 known species of metatherians (marsupials and their closest relatives) from the Cretaceous of North America — including Didelphodon — were almost all identified through fragments of jaw bones or teeth, providing a limited glimpse into marsupials’ closest relatives. These four fossils include a nearly-complete skull from the North Dakota Geological Survey State Fossil collection, a partial snout and an upper jaw bone from the Burke Museum’s collections, and another upper jaw from the Sierra College Natural History Museum.


To test the bite force of Didelphodon,  Abby Vander Linden, then a UW Biology research technician working with UW biology professor and Burke Museum curator Sharlene Santana, CT-scanned the fossils and compared the gaps in reconstructed skulls where jaw muscles would go to those of present-day mammals with known bite forces. Bite force measurements indicate that, pound-for-pound, Didelphodon had the strongest bite force of any mammal that has ever lived. In addition to the bite force, Didelphodon‘s canines were similar to living felines and hyenas — suggesting they could handle biting into bone, biting deep and killing prey. Its shearing molars and big rounded premolars, combined with powerful jaws and jaw muscles, indicate it had a specific niche in the food web as a predator or scavenger capable of crushing hard bone or shells, and was capable of eating prey as big as it was — even possibly small dinosaurs.

Co-author Jonathan Calede, former UW biology graduate student and now a visiting assistant professor at Bucknell University, also examined “microwear” patterns, or tiny pits and scratches on the specimens’ teeth, to indicate what the animals were eating as their “last suppers” a few days before the animals died. By comparing the microwear patterns from Didelphodonto the teeth of other fossilized species and current-day mammals from the Burke’s mammal collection, Calede found Didelphodon was an omnivore that likely consumed a range of vertebrates, plants and hard-shelled invertebrates like mollusks and crayfish, but few insects, spiders, earthworms or leeches.

“The interesting thing about these fossils is that they allowed us to study the ecology of Didelphodon from many angles,” said Calede. “The strength of the conclusions come from the convergence of microwear with bite force analysis, studies of the shape and breakage of the teeth, as well as the shape of the skull as a whole.”


Read full article in UW Today

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