An ancestor of humans -- albeit one that is at the root of our family tree -- shared the planet with dinosaurs, a new study concludes.
This ancestor, the first placental mammal, lived between 88.3 to 91.6 million years ago, according to the study, published in the latest issue of Biology Letters. Placental mammals today include humans and all other mammals except those that lay eggs or have pouches (marsupials).
The study counters prior research, based solely on fossil evidence, which theorized this "mother of all placental mammals" arose after the dinosaurs died out. The researchers instead believe that it preceded the non-avian dino die off and that we wouldn't even be here if the dinosaurs were still around.
"When dinosaurs died out, many ecological niches became vacant, and placental mammals took over," lead author Mario dos Reis told Discovery News. "The placental ancestor diversified and evolved into the modern mammals we see today, such as rodents, deer, whales, horses, bats, carnivores, monkeys and ultimately humans."