Researchers Discovered 60-Million-Year-Old Fossil of Giant Possum in Texas's Big Bend National Park

Texas is now home not only to cowboys but also to a unique fossil specimen from "Swaindelphys." This possum-like specimen was dated back to 60 million years ago, and per its features, it was possibly the largest marsupial in North America during that period. Initially, experts thought that the specimen belonged to either the group of large Cretaceous metatherians or Eocene metatherians. However, both possibilities were later proven wrong. A study published in the Journal of Vertebrate Paleontology identified that the specimen belonged to the Swaindelphys genus, a group of ancient near-marsupials. Along with being the largest, the species was detected as the youngest among all the metatherians living at that time.

Discovery of Swaindelphys Solastella

The specimen was found in the Big Bend National Park, according to Discovery Magazine. This place is known for being a fossil reservoir, as multiple sets of remains have been unearthed from the area for decades. Researchers named the newly found Paleocene era specimen "Swaindelphys solastella." The new specimen was the size of a modern-day hedgehog. Chris Beard, senior curator with KU's Biodiversity Institute and Foundation Distinguished Professor, called the discovery "notable" due to its standout size among all the marsupials of the Paleocene period. 

For the examination, researchers compared specimens from Big Bend National Park to Paleocene marsupials in the custody of the LSU and the University of Texas at Austin, per the press release. The comparative analysis rejected the previous assertions that the remains belonged to the group of large Cretaceous metatherians or Eocene metatherians. Instead, it indicated that the fossils were part of a large species of Swaindelphys. 

Connection to Primates

Researchers also found a link between the features of this specimen and ancient North American primates, according to ABC News. "I call them 'primatomorphans,'" Beard shared. "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." Hence, insights about the creature also open a window into the trajectory of primates in the world. If experts can learn more about the behavior and geographic locations of species like "Swaindelphys solastella," they can correlate it with the existence of Paleocene era primates. They are most interested in identifying the species' distribution pattern to figure out the factors and barriers that were at play during habitat selection for them. This can also reveal how primates at that time conducted their migrations and eventually spread all across the world. 

Texas: a Habitat for Swaindelphys Solastella

Researchers believe Texas's climate was more tropical in the Paleocene era than it is today. That climate possibly facilitated many rivers and streams in the area. According to the study, "Swaindelphys solastella" was detected in an area that might have been a river in the past. The river helped the species in their life functions, but also, in certain ways, limited them. Over time, rivers like these shifted south, creating a boundary of sorts, which could have been difficult for ancient marsupials and primates to cross. It likely prevented them from spreading to nearby places such as the Bighorn Basin in Wyoming. 

Lead author Kristen Miller wants to investigate the area to understand the different features of beings on both sides of the supposed boundary. Some differences have already been noted. "North of that ancient divide, we see the classic Bighorn Basin taxa in their expected time periods," Miller 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." The team believes that further investigation in the area will eventually reveal what geographical and environmental factors shaped the life of this species.