Zhe-Xi Luo, a professor of organismal biology and anatomy at the University of Chicago, and his team recently discovered a 160-million-year-old skeleton in the Tiaojishan Formation, northeast of Beijing.
The well-preserved complete fossil, Rugosodon eurasiaticus, is believed to be the oldest ancestor of the multituberculate family tree and is considered to be the evolution's most successful ancient mammal.
"Most of these types of fossils date back from 55 [million] to 100 million years ago," said Luo.
The fast-running, agile omnivore, rodent-like creature resembles today's African dormouse. They were just bigger and less cuddly.
Based on the location from where the fossil bone was unearthed, scientists suggest that the creatures lived on the shores of a lake.
Greg Wilson, an assistant professor of biology said that these animals were both able to live and reproduce successfully alongside dinosaurs during the Jurassic period.
"Other mammals were cowering in [the dinosaurs'] shadows, but the multituberculates were unfazed," Wilson said.
"They had an incredibly long history," said Luo. "They lived with dinosaurs for 100 million years, and outlived them too."
The Jurassic rat was able to have a healthy survival rate because it had key adaptive features. Their diet consisted of plants and small animals. They had flexible legs and highly rotatable ankle joints.
"The ankles, finger bones and the first big toe are all capable of a wide range of motion," said Luo. "This lets them do all sorts of things, like climb trees and dig tunnels. The teeth have a lot of creases and grooves, which lets them feed on seeds and fruits but also on insects and worms. The teeth are very interesting and very cute."
Luo's recent research has been published in last week's issue of Science that focused on the teeth and ankle bones.
"The analysis of the ankle was quite thorough," said Wilson. "But other aspects of the limbs and claws would tell us more about how it moved around in its environment. Some of us [researchers] are waiting for a more detailed analysis."
