Small Mammal was Early

Juramaia’s incredibly wellpreserved teeth had things in common with modern placental mammals. ZHE-XI LUO/CARNEGIE MUSEUM OF NATURAL HISTORY

Asmall, rat-like creature ended up settling a debate between palaeontologists and geneticists. Via DNA from modern animals, geneticists had calculated that the placental mammals, whose embryos are nurtured through the placenta, originated 160 million years ago, but palaeontologists thought that the fossils pointed at a later date 125 million years ago.

In 2011, the fossil of the only 15 g Juramaia placental animal was discovered, proving geneticists right with an age of 160 million years. According to scientists, the small creature led an active life between the branches of trees, catching insects, etc. On the ground below Juramaia, large dinosaurs roamed the world.

High metabolisms, sharp senses, and quite large brains made the mammals a very successful group of animals – even in Juramaia's era. Still, almost 100 million years passed, before a huge meteor strike seriously sped up the evolution of mammals.