Scientists determined some of the world's earliest mammals lived in trees by looking at their anklebones.
The 65-million-year-old mammal Purgatorius lived on a diet of fruit and insects and first appeared in the fossil record shortly after the extinction of non-avian dinosaurs, Yale University reported. In the past researchers thought these animals started out on land and moved to the trees later on, but these new findings dispute the popular theory.
"The textbook that I am currently using in my biological anthropology courses still has an illustration of Purgatorius walking on the ground. Hopefully this study will change what students are learning about earliest primate evolution and will place Purgatorius in the trees where it rightfully belongs," said Stephen Chester, the paper's lead author.
Chester, who conducted much of the research while at Yale University studying for his Ph.D., is an assistant professor at Brooklyn College, City University of New York. Chester is also a curatorial affiliate at the Yale Peabody Museum of Natural History.
Until recently, Purgatorius' teeth and jaw bones were all the only fossils available for study, but scientists identified samples of the animals ankle bones taken sites in northeastern Montana. This allowed the researchers to gain new insights into how the early mammals lived.
"The ankle bones have diagnostic features for mobility that are only present in those of primates and their close relatives today," Chester said. "These unique features would have allowed an animal such as Purgatorius to rotate and adjust its feet accordingly to grab branches while moving through trees. In contrast, ground-dwelling mammals lack these features and are better suited for propelling themselves forward in a more restricted, fore-and-aft motion."
These findings represent the oldest known fossil evidence that arboreality played a significant role in primate evolution. The findings suggest the divergence of primates and other mammals was not as drastic as was previously believed, and most likely came about through gradual and subtle changes.
The findings were published Jan. 19 in the Proceedings of the National Academy of Sciences.
