Mammal Ancestors Lived High, Low, Chewed Gum

Ancestors of the earliest known tree-dwelling, as well as subterranean mammals have just been discovered in China.

The fossils, described in the journal Science, suggest that the wide-ranging ecological diversity of modern mammals had a precedent more than 160 million years ago.

“We consistently find with every new fossil that the earliest mammals were just as diverse in both feeding and locomotor adaptations as modern mammals," Zhe-Xi Luo, a co-author of both papers, said in a press release. "The groundwork for mammalian success today appears to have been laid long ago."

Luo, a professor of organismal biology and anatomy at the University of Chicago, and colleagues studied the animals’ remains and named two new species: Agilodocodon scansorius and Docofossor brachydactylus.

Based on the finds, Agilodocon is the first known tree-dwelling “mammaliaform,” which refers to the long-extinct relatives of modern mammals. It lived about 165 million years ago and had hands and feet with curved horny claws. Its limb proportions were typical for mammals that live in trees or bushes.

Its spade-like front teeth, which could gnaw into bark, were adapted for feeding on the gum or sap of trees. Some modern New World monkeys possess similar teeth. Agilodocodon also had well-developed, flexible elbows and wrist and ankle joints that allowed for much greater mobility. These are all characteristics of climbing mammals.

"It's amazing that these arboreal adaptions occurred so early in the history of mammals and shows that at least some extinct mammalian relatives exploited evolutionarily significant herbivorous niches, long before true mammals," said study co-author David Grossnickle, a graduate student at the University of Chicago.

Docofossor, which lived around 160 million years ago, looked a lot like the modern African golden mole. Docofossor had shovel-like fingers for digging, short and wide upper molars typical of mammals that forage underground, and a sprawling posture indicative of subterranean movement.

Together, the two early mammal ancestors provide strong evidence that arboreal and subterranean lifestyles evolved early in the evolutionary history of our mammal ancestors. Clearly, these scrappy animals were making the most out of all habitat possibilities.

Read more at Discovery News