Giant Groundhog Skull from the Age of Dinosaurs Reveals How Mammals Evolved

Imagine a groundhog that weighs 20 pounds or more. Now imagine that groundhog living during the age of the dinosaurs. Paleontologists have uncovered the fossil remains of a large, 66 to 70-million-year-old groundhog-like creature that could give insight into mammalian evolution during that time.

"We know next to nothing about early mammalian evolution on the southern continents," said David Krause, one of the researchers, in a news release. "This discovery, form a time and an area of the world that are very poorly sampled, underscores how very little we know. No paleontologist could have come close to predicting the odd mix of anatomical features that this cranium exhibits."

The newly discovered animal is called Vintana sertichi. Belonging to a group of early mammals called gondwanatherians, it was a titan at its time. Vitana's skull measures almost five inches long, which is twice the size of the previously largest known mammal skull during the Age of the Dinosaurs. It was about twice or even three times the size of an adult groundhog, and had long, scimitar-shaped flanges for the attachment of massive chewing muscles.

Vintana was likely a large-eyed herbivore with a keen sense of hearing and smell. What's more interesting is that the scientists were able to show that Vintana and other gondwanatherians were close relatives of multituberculates, which were the most successful mammalian contemporaries of dinosaurs on the northern continents. Gondwanatherian and multituberculates also grouped with the Haramiyida, another taxon. This three-group clustering reveals a bit more about how mammals first evolved.

"The new study of Vintana is a giant leap forward toward resolving the long-standing mystery of gondwanatherian mammals, which has puzzled paleontologists for decades," said Zhe-Xi Luo, one of the researchers. "Vintana is also a galvanizing discovery for the future decades. With features so remarkably different from those of other mammals previously known to science, this fossil tells us how little we knew about the early evolution of mammals-it will stimulate paleontologists to conduct more field exploration in order to advance the frontier of deep time history and evolution."

The findings are published in the journal Nature.