|The little tree-climber, Agilodocodon scansorius|
Two new fossil discoveries push the timeline back on the appearance of burrowing and tree-climbing mammals. Fossils of the shrew-sized creatures found in China date to the age of the dinosaurs and show that mammals of that period were already highly specialized, well-performing animals. One of the rodent-like animals was likely a long-clawed tree-dweller, while the other was shovel-pawed tunnel-digger.
The little tree-climber, Agilodocodon scansorius, is the earliest arboreal mammal ever discovered. A report published this week in Science Magazine highlights its traits suited for its habitat, including long claws, spade-like front teeth for gnawing into bark, and flexible elbows and ankles. It is believed to have weighed up to 40 grams, a bit less than a typical hotdog without condiments, and lived about 165 million years ago in what is Mongolia today.
“When we got into the study of Agilodocodon, we realized that the outline for the horny sheath of the claws is preserved,” Zhe-Xi Luo, professor of organismal biology and anatomy at the University of Chicago, said in an interview. “Those soft tissues are not preserved in the vast majority of mammals. It has a very long, curved narrow claw — one feature to show that it is a good climber.”
In a report published in the same issue of Science, the other mammal, called Docofossor brachydactylus, is described to have stood no more than 9 centimeters tall and weighed only 17 grams, about the size of a juvenile mouse. Docfossor is the earliest underground-dwelling mammal ever found and shares similarities with the African golden mole, having short, wide digits suitable for digging. The little digger is estimated to have lived some 160 million years ago in what is today Ganggou Fossil Site in China’s Hebei province.
Both fossils are of creatures that belong to the order Docodonta. The discoveries are the first to provide full skeletons of this order, which had previously been characterized by evidence from fossils of teeth, jaws, and bits of skull.