160 Million-Year-Old Mammal Fossil Reveals Secret to Successful Evolution

Scientists are learning a little more about how mammals became so successful. They've uncovered a 160 million-year-old fossil of an extinct rodent-like creature from China that reveals how multituberculates, the most evolutionary successful and long-lived mammalian lineage in the fossil record, achieved their dominance.

Multituberculates flourished during the Cretaceous era, which ended about 60 million years ago. They were similar to today's rodents, filling a wide variety of niches that extended below ground, on the ground and even in trees. The latest fossil is actually the oldest ancestor in the multituberculate family tree and looks a bit like a chipmunk or a small rat. Its teeth were adapted to gnawing both plants and animals and it possessed ankle joints that were highly adept at rotation. In fact, it's very likely that this creature, known as Rugosodon eurasiaticus, paved the way for later plant-eating and tree-dwelling mammals.

"The later multituberculates of the Cretaceous and the Paleocene are extremely functionally diverse: Some could jump, some could burrow, others could climb trees and many more lived on the ground," said Zhe-Xi Luo, co-author of the new study, in a news release. "The tree-climbing multituberculates and the jumping multituberculates had the most interesting ankle bones, capable of 'hyper-back-roation' of the hind feet."

Multituberculates first appeared during the Jurassic period and lasted for about 100 million years before finally becoming extinct during the Oligocene epoch. That's when the creatures were outcompeted by more modern rodents. Despite going extinct, though, multituberculates were still some of the most successful mammals to have existed on Earth.

The new fossil reveals a little bit more about this category of animals. More specifically, it extends the distribution of certain multituberculates from Europe to Asia during the Late Jurassic period. It shows exactly how widespread multituberculates were and also reveals how these creatures developed unique adaptations, such as their teeth and locomotive skills, to help propel them to dominance.

The findings are published in the journal Science.