A tiny mammal that weighed less than a chipmunk and coexisted with dinosaurs may have been an ancient forerunner to mammals and eventually humans, according to a new study.
Scientists working in Northeast China discovered the fossil of the diminutive Juramaia sinensis, which means the Jurassic mother from China, and dated the remains to about 160 million years ago, some 35 million years before the previous find for earliest mammalian ancestor.
The great evolutionary lineage that includes us had a very humble beginning, in terms of body mass, Zhe-Xi Luo, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh who led the team that discovered the fossil, told National Geographic.
The find offers a clue to when mammals split into placental mammals -- animals, like humans, that give birth to relatively developed young which are nurtured in the womb through nutrient-rich placenta -- and marsupial mammals, animals like kangaroos that spend less time pregnant and produce less mature babies.
The fossil includes a preserved set of teeth and forepaw bones that scientists believed were closer to the anatomy of placental mammals than marsupials. Luo said that it likely used its claws to scurry up trees and its teeth to eat insects, an existence that would have allowed it to endure and elude larger predators.
Once you get out on a tree, you have all the different ecological opportunities that weren't available for the terrestrial animals, he said.
The finding corroborates DNA studies, conducted using molecular evidence, which also suggested that the evolutionary split occured about 160 million years ago.