Two papers published in Nature disagree on when mammals evolved but also broaden the portrait of mammalian evolution.
April Isch/University of Chicago
Once, somewhere in what is now China, lived an animal with the fur and teeth – and poisonous spur – of a mammal, but with the ears and ankles of a reptile.
Called Megaconus, the 165-million-year-old precursor to modern mammals and companion to feathered dinosaurs is a new data point in paleontologists’ search to pinpoint how and when the features of modern mammals evolved. The animal, described in a paper published in Nature, suggests that mammalian characteristics well predated the existence of actual mammals.
But at the same time, a separate paper published in Nature has classified another fossil in the same lineage to which Megaconus belongs not as a mammal precursor, but as a true mammal, a finding that would dial back the evolution of mammals some 50 million years. The conflicting findings underscore the difficulties of piecing together the still enigmatic evolution of mammals.
Zhe-Xi Luo, a professor of organismal biology and anatomy at The University of Chicago and an author on the first paper, likens the evolution of mammals to a “vast bush” made of about two-dozen branches, the majority of which were “pruned in extinction.” Just three of those branches were spared natural selection's gardener’s shears and now form the three lineages of modern mammals.