WASHINGTON (Reuters) – A fossilized skull of a small creature found under a dinosaur foot bone in Utah provides insight into one of the most primitive mammalian groups, allowing scientists to rethink the timing of the dissolution of the long-gone supercontinent, Pangea.
Scientists on Wednesday described the skull of a small primitive mammal of the Cretaceous called Cifelliodon wahkarrmoosuch, about the size of a small hare, 130 million years ago lived with qualities that suggest that it has a pronounced sense of smell and may have been nocturnal.
"It's an herbivore, as we can see from its herbivorous teeth," said paleontologist at the University of Chicago Zhe-Xi Luo. "Of the sediments in which it was preserved, it probably lived on the banks or the floodplain of a small river."
The three-inch (7.5 cm) skull was well-preserved and almost complete, unlike the usual scarred fossils from the group that included cifelliodone, called haramiyidans.
The earliest primitive mammals evolved during the Triassic period, when dinosaurs first appeared, from creatures that combined reptilian and mammalian features.
The Haramiyidans appeared near the dawn of the mammal line, with the earliest known representative who lived about 208 million years ago and the last known member about 70 million years ago.
The skull was unknowingly unearthed at a point north of Arches National Park in eastern Utah. The Utah Geological Survey paleontologists did not know that they were buried in a rock that was brought to a lab for study until they looked under the foot bones of a two-legged herbivorous dinosaur called Hippodraco.
It could be the best preserved skull of a Haramiyidan and provide a new understanding of the group.
"Compared to modern mammals, cifelliodone had a simple, tubular brain that lacked complex bone structures normally associated with the anterior part of the brain's body and nasal region and had simple tooth roots alongside other primitive features." Southern California paleontologist Adam Huttenlocker said.
Before a geological process called plate tectonics turned them into separate land masses, the Americas, Eurasia, Africa, Antarctica, Australia and India were all part of a large, single continent called Pangea. The time for Pangea's separation, initially into two large land masses, was the subject of a scientific debate.
The researchers said that the discovery of cifelliodone, which had a close relative in Africa, suggests that there were 15 million years later connections between the continents of the northern hemisphere and those in the southern hemisphere than previously thought.
The research was published in the journal Nature.
Reporting by Will Dunham; Arrangement by Sandra Maler