It may have weighed only 2 1/2 pounds and stood about 6 inches tall, but the discovery of a half mammal, half reptile's skull in eastern Utah has huge implications for geologic timelines.
The skull of the new species, Cifelliodon wahkarmoosuch, came from a snout-bearing, catlike animal with buck teeth and molars for crushing plants.
Its discovery is evidence that the super-continental split of Pangea likely occurred more recently than scientists previously thought - 15 million years later - and that a group of reptile-like mammals experienced an unsuspected burst of evolution across several continents.
"Based on the unlikely discovery of this near-complete fossil cranium, we now recognize a new, cosmopolitan group of early mammal relatives," said Adam Huttenlocker, lead author of the study and assistant professor of clinical integrative anatomical sciences at the Keck School of Medicine of the University of Southern California.
The study was published in the journal Nature on May 16 and updates the understanding of how mammals evolved and dispersed across major continents during the age of dinosaurs.
This creature, although it was covered in hair and suckled its young, laid eggs like the modern-day platypus.
"For a long time, we thought early mammals from the Cretaceous (145 million to 66 million years ago) were anatomically similar and not ecologically diverse," Huttenlocker said. "This finding by our team and others reinforce that, even before the rise of modern mammals, ancient relatives of mammals were exploring specialty niches: insectivores, herbivores, carnivores, swimmers, gliders. Basically, they were occupying a variety of niches that we see them occupy today."
Andrew R.C. Milner, a paleontologist at the St. George Dinosaur Discovery Site at Johnson Farm, discovered the skull site on Bureau of Land Management Lands northeast of Arches National Park. Later paleontologists unexpectedly found the skull in the lab under the foot of a new iguanodont dinosaur called Hippodraco.
The fossil discovery emphasizes that these type of animals and some other vertebrate groups existed globally during the Jurassic-Cretaceous transition, meaning the corridors for migration via Pangean landmasses remained intact into the Early Cretaceous.
Most of the Jurassic and Cretaceous fossils of these type of animals are from the Triassic and Jurassic of Europe, Greenland and Asia.
David Grossnickle and Julia Schultz, from the University of Chicago, contributed to the study, as well Jim Kirkland, state paleontologist with the Utah Geological Survey.
The specimen was found on Bureau of Land Management lands and is held in public trust at the Natural History Museum of Utah, where it is on display in the museum's Past Worlds Gallery.
The federal government provided $300 for the research. The remainder was supported by the state of Utah.