Placental mammals like elephants, bats and humans evolved from small, insect-eating mammals, a study led by Stony Brook University has found. The research resolves many questions of mammal evolution.
Comparing both DNA and body shapes, the researches found placental mammals arose after the extinction of the dinosaurs. Previous thought based on genetics held that placental mammals evolved while dinosaurs still lived.
The study also suggests that African mammals such as elephants evolved in the Americas and dispersed into Africa. How they did so remains a mystery.
Caroline Copley
student
Excuse my ignorance but weren't mammoths progenitors of elephants and therefore isn't the mechanism easy as mammoths were in the Americas, the Andes I think. And wouldn't there migration into warmer climes result in their evolution into more modern forms??
Very clearly however our marsupials and monotremes have a considerably longer history. Marsupial fossils have been found in Alberta Canada from about 100 mill years ago methinks, although more recent finds in China might be earlier. Also I think there might be pretty solid evidence for monotremes too. Therefore our lot have already ridden one wave of extinctions and are more ready than eutherians such as ourselves for the next!
Don Gibbons
Clerk
Hi Caroline
I think what this brief refers to as "African mammals such as elephants" refers to the c.65 mega year ancestor of a group referred to as Afrotheres, whose living representatives include elephants, sirenians, hyraxes, aardvarks and sengis, which have traditionally been thought to have originated in Africa, or nearby on the northern shores of the Tethys Sea in what is now Asia. Mammoths (Mammuthus) were not the ancestors of elephants, rather they shared a common ancestor with "Asian" elephants (Elephas) in Africa about 6 mega years ago, their shared lineage having split from African elephants (Loxodonta) in Africa about 2 mega years before that. Loxodonta appears to have remained in Africa, while Elephas and Mammuthus spread widely. Mammuthus entered the Americas. It was more distantly related proboscideans, the gomphotheres, that diversified in South America in the last 6-8 megayears, only becoming extinct there about 10 thousand years ago.