All of that information went into a gigantic Web-based database called MorphoBank, in which the scientists recorded more than 4,500 individual traits, both physical and behavioral, culled from 86 placental mammal species, about half of them extinct. “I was working in one cell [of the database],” recalls Novacek, “when another was suddenly populated with information that was being entered in real time by a collaborator from Brazil. It was really exciting.”

MorphoBank established the species relationships among placental mammals, while DNA and fossil-dating calculations established the timeline — and while that sounds simple enough, it was, says Novacek, “hugely laborious.” Indeed, writes Duke University biologist Anne Yoder in a Science commentary, “O’Leary et al.’s study offers a level of sophistication and meticulous analysis of morphological and paleontological data that is unprecedented.”

All that impressive brainwork led us back to a rather humbling place: You, your loved ones and your friends, not to mention Abe Lincoln, Winston Churchill, Napoleon, Babe Ruth, Marilyn Monroe—all of us, in other words—are the multi-multi-generational grandkids of a rat-like, half-pound, furry-tailed bug-eater.