Health & Science

The mammal that inherited the Earth; A Great Lakes crisis; Reducing the risk of autism; Moose dying in droves

The mammal that inherited the Earth

The common ancestor of almost all mammals on Earth today—including human beings—was a furry, long-tailed, rat-sized creature that emerged after the extinction of the dinosaurs. In a six-year study that collated vast amounts of data on anatomical traits throughout the mammalian family tree, researchers discovered that all modern mammals that nourish their unborn young through a placenta—including bats, cats, elephants, whales, and humans—evolved from a single insect-eating, tree-climbing species called Protungulatum donnae. “This is a landmark piece of work,” paleontologist Stephen Brusatte of the University of Edinburgh tells New Scientist. Previous research has suggested that several lines of placental mammals co-existed with the dinosaurs, but the new study backs the hypothesis that they emerged only after an asteroid 66 million years ago killed off most of the massive reptiles, paving the way for a mammalian takeover beginning 200,000 to 400,000 years later. The new timeline suggests that the first placental mammal is 36 million years younger than previously thought, says John Gatesy, an evolutionary biologist at the University of California, Riverside—a finding that “will surely be controversial” because it clashes with dating derived from genetic evidence.

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