(BIG BEND NATIONAL PARK, Texas) — Paleontologists have found fossilized remains of a giant possum-like mammal that lived 60 million years ago.
The fossils, found at Big Bend National Park in Texas, belong to a group of ancient near-marsupials from the Paleocene period that scientists call Swaindelphys, according to a paper published last week in the Journal of Vertebrate Paleontology.
The prehistoric species, called Swaindelphys solastella, was “gigantic” compared to other Swaindelphys at the time but are actually about the size of a modern hedgehog, according to the researchers.
“I compared them to a lot of other marsupials from around the same time period to see what they’re most closely related to,” said Kristen Miller, a doctoral student at The University of Kansas’ Biodiversity Institute and Natural History Museum and lead author of the paper, said in a statement.
At first, the paleontologists thought the fossils belonged to a group of metatherians — or marsupial-like mammals — from the Cretaceous period that survived the Cretaceous-Paleogene extinction, the mass extinction event believed to have wiped dinosaurs from the planet 66 million years ago.
But additional analysis revealed that the specimens belonged to a “surprisingly large” new species of Swaindelphys.
“Not only are they the largest metatherians from this time period, but they’re also the youngest and located at the most southern latitude,” Miller said.
The new fossil is the largest marsupial — in terms of body and size — found so far in North America from the Paleocene period, Chris Beard, senior curator with KU’s Biodiversity Institute, said in a statement.
“Since everything is bigger in Texas, this is perhaps not surprising,” Beard said.
“I call them ‘primatomorphans,'” Beard said. “They’re not, technically speaking, primates, but they’re very close to the ancestry of living and fossil primates. These marsupials are probably ecological analogues of early primates.”
The researchers’ work is aimed at uncovering some of the smaller and harder-to-find fossil mammals that lived at Big Bend at the time, Beard said.
The paleontologists are also interested in the differences in the kinds of fossils found in more northern regions, such as Wyoming and Alberta, Canada.
“North of that ancient divide, we see the classic Bighorn Basin taxa in their expected time periods,” Miller said said. “But south of that, in river drainages that originate in the central Rockies and areas farther to the south, things start to go a little wacky.”
More research into Swaindelphys solastella, as well as new fieldwork in Big Bend, is planned.
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