Jennifer Cavin was uncasting a large dinosaur fossil excavated in southeastern Utah, removing the protective plaster, when she made a discovery within the discovery.
“Come over here,” she yelled from across the lab, brushing away bits of dust and rock.
“I think I found another skull.”
There, tucked beneath the foot of the herbivore she was working on, was a fossilized cranium. The weird thing: It didn’t appear to belong to a reptile. Jim Kirkland knew that almost immediately when he rushed over to see it. This wasn’t like the other dinosaurs — lizards and raptors — they’d been uncovering. The state paleontologist was stunned.
Whatever the critter was, Kirkland told Cavin, it was more like a mammal than anything else. And it would have implications for what science has believed to be the timing of the breakup of the supercontinent Pangaea.
“We’ve never found a mammal there in these rocks before,” he said last week, after publishing the finding in a paper this month in the journal Nature. “This one skull turns out to be a complete oddball.”
Scientists unearthed the fossil in rock from the Cretaceous period, which was 145 million to 65 million years ago. The timeframe of the skull — dated at 130 million years old — shatters previous conceptions about when the continents split, indicating that happened possibly 15 million years later than previously thought.
That’s because the mammal-like skull found in 2006 just north of Moab on Bureau of Land Management property is a haramiyid. It was known that the hairy, rabbit-like creatures roamed Eurasia during the Triassic and Jurassic periods, as well as the early Cretaceous (when the land masses had completely drifted apart). But there had never been evidence that they were in North America at that time.
“It’s geographically very important,” said Zhe-Xi Luo, one of the paper’s authors, a paleontologist at the University of Chicago and an expert on haramiyids. “The fossil is a good link of the different continents at a very critical time of the Earth’s history.”
Finding remnants of the species spread so far apart means it either wandered over still-connected land masses or island-hopped during low sea levels. Either way, it’s a dramatic discovery with implications for the final possible moment of migration.
The critter, which has been named Cifelliodon wahkarmoosuch, would have been an early relative of mammals, at the doorstep but not quite inside yet. It is similar to a platypus, laying eggs and nursing its young. It had buck teeth, a shallow snout and short legs.
Its skull measures about 3 inches across — which is large for a mammal during the Mesozoic period (spanning Triassic, Jurassic and Cretaceous). Most were the size of mice — and mostly just their teeth have been found. “For the age of this animal, it’s gigantic,” Kirkland said. “It’s Godzilla.”
The fossil is on display now at the Natural History Museum of Utah. CT scans showed it likely had a small brain and a good sense of smell.
It was found under the foot of a Hippodraco, or water dragon. But that doesn’t mean the creature was stepped on and crushed to death. Only the top part of the mammal’s skull — no lower jaw — was found at the site, meaning it likely washed up there.
“It was just kind of random, but I love the fact it was under the foot of this fully articulated dinosaur we were working on,” Kirkland added. “The serendipity.”
Cavin found two other skulls in the area — what Kirkland jokingly calls a “rinky dink site” — including a unique crocodilian fossil. Neither, though, made her shout as loud as the mammal discovery.