For years, scientists believed that the only mammals alive during the Jurassic Period, roughly 145 million to 200 million years ago, were small, shrewlike creatures with few distinguishing features other than a sophisticated set of molars.
But in 2006, that assumption was upset with the discovery of a larger, beaverlike mammal that lived about 164 million years ago. Now, researchers have discovered two fossils that further expand the menagerie of Jurassic mammals, collectively known as docodons.
Each of the animals seems to have adapted to an environmental niche, researchers reported in two papers in the journal Science. One had skeletal features consistent with tree living, such as incisors for eating tree gum and sap. The other had shortened digits, sprawling limbs, large claws and ribs resembling those of modern digging animals.
“We used to view docodons as a relatively homogeneous group,” said Zhe-Xi Luo, a paleontologist at the University of Chicago and an author of both papers. “Now we’ve found a tree climber with specialized teeth and a super digger that was clearly subterranean. Clearly this group, despite the fact that they came and went, had their own very interesting biological diversities.”
The findings help refute the idea that the presence of dinosaurs stunted the evolution of early mammals, he added. “This shows interesting evolution can still happen with mammals despite the dinosaurs.”