A new database and study drew on 4,500 anatomical traits of live and fossilized species as well as DNA to explore the evolutionary relationships between mammals, all the way back to a hypothetical predecessor to all placental species, an animal that resembles a shrew. The resource was designed to grow as data from additional fossil and genetic finds are uncovered. Expert David Archibald summarized the significance of the findings: "The explosive model for placental evolution did not come about until after the extinction of dinosaurs. I think that's the big finding. All orders we are familiar with, even if you are not trained in biology -- primates, elephants, whales -- all groups show up within 10 million years of the end of the age of dinosaurs."
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