160 million-year-old mammalian ancestor discovered

Scientists in China have unearthed a nearly complete skeleton of a 'Jurassic rat' - a 160 million-year-old creature - which they say is one of evolution's most successful mammal.
The fossil of the extinct rodent-like creature is helping to explain how multituberculates - the most evolutionarily successful and long-lived mammalian lineage in the fossil record - achieved their dominance, researchers said.
This fossil find - the oldest ancestor in the multituberculate family tree - represents a newly discovered species known as Rugosodon eurasiaticus.
The fossil unearthed by Chong-Xi Yuan from the Chinese Academy of Geological Sciences in Beijing and colleagues reveals teeth that were adapted to gnawing plants and animals alike, as well as ankle joints that were highly adept at rotation.

Researchers suggest that R eurasiaticus paved the way for later plant-eating and tree-dwelling mammals.
The multituberculates flourished during the Cretaceous era, which ended over 60 million years ago.

Much like today's rodents, they filled an extremely wide variety of niches-below the ground, on the ground and in the trees-and this new fossil, which resembles a small rat or a chipmunk, possessed many of the adaptations that subsequent species came to rely upon, the researchers said.
"The later multituberculates of the Cretaceous (era) 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, a co-author of the study.

"The tree-climbing multituberculates and the jumping multituberculates had the most interesting ankle bones, capable of 'hyper-back-rotation' of the hind feet," said Luo.
"What is surprising about this discovery is that these ankle features were already present in Rugosodon - a land-dwelling mammal," he said.
Such highly mobile ankle joints are normally associated with the foot functions of animals that are exclusively tree-dwellers-those that navigate uneven surfaces, researchers said.
R eurasiaticus could eat many different types of food, they said.
The fossil-particularly its dentition, which reveals teeth designed for shearing plant matter confirms a 2012 analysis of tooth types that suggested multituberculates consumed an animal-dominated diet for much of their existence, later diversifying to a plant-dominated one.

Multituberculates arose in the Jurassic period and went extinct in the Oligocene epoch, occupying a diverse range of habitats for more than 100 million years before they were out-competed by more modern rodents.
The study was published in the journal Science.