Researchers now suggest that the last common ancestor of today’s placental mammals, the group in which human beings, whales and armadillos fall, was probably “a shrew-like creature with a long snout.”
Scientists believe that the ancestors of the placental mammals had separated from what eventually evolved into reptiles about 320million years ago. They argue that it was not until between 70 and 80million years ago when placental mammals emerged.
That mentioned, scientists recently analysed, in a paper published in the journal Science, the skulls of at least 300 species of “extinct and living placental mammals” in an effort to understand the trend in their evolution.
Notably, the results argue that placental mammals most likely got their break around the time of the mass extinction 66million years ago, when, as Guardian’s heath correspondent Nicola Davis observes, an asteroid ploughed into Earth and wiped out the non-avian dinosaurs and a host of other life.
Prior to this time, researchers highlight, the ancestors of the major groups representing today’s placental mammals all had similar shaped skulls.
Prof Anjali Goswami from the Natural History Museum and the lead author of the research observes that: “there is a huge boom, in terms of mammal diversification, right after the boundary, or right around that boundary – depending on when you think [placental] mammals actually originated.”
In addition, Goswami highlights that the repeated peaks were likely “to have been linked to climate events opening up new opportunities for mammals.” “Their diminishing nature over time is probably because such niches became increasingly occupied by existing species,” she says.
The researchers equally note that among other discoveries, “herbivores evolved more rapidly than carnivores and social animals more quickly than solitary ones. “You don’t really see much change in the carnivores because they’re just eating whatever animal is around regardless of what that animal is eating itself,” Goswami argues.
“Before then, mammals were background characters in a dinosaur drama, slowly but surely evolving in the shadows, chugging along…Then the asteroid hit and mammals nearly went the way of the dinosaurs, but a handful of species were able to survive, including distant but direct ancestors of ours,” Prof Steve Brusatte, a paleontologist at the University of Edinburgh and author of The Rise and Reign of the Mammals, said in response to the findings of the research.
