The blue whale—190 tonnes in weight and beautifully adapted for swimming—is a placental mammal. The mammal bit means that mothers nourish their babies with milk after they’re born. The placental bit means that mothers nourish their babies via a placenta before they’re born—an organ that allows them to exchange oxygen and nutrients without also swapping blood.
The bumblebee bat—1.5 grams in weight and beautifully adapted for flying—is also a placental mammal. So are you. So is a bear, an anteater, a giraffe and a squirrel. Also: armadillos, rhinos, rabbits, manatees, and pangolins.
All of these creatures, in their wondrous array of shapes and sizes, evolved from a small, unassuming, scurrying insect-eater that lived a few hundred thousand years after the apocalypse that finished off most of the dinosaurs.
A team of US scientists have now reconstructed what this ancestral placental was like, to an extraordinary level of detail. They have predicted how much it would have weighed, the number of molars in its jaws, the shape of its sperm, and the path that its carotid artery took up its neck. None of this comes from a fossil of the creature itself. Instead, the predictions are based on 80 of its descendants, including some that are still alive and others that joined it in extinction. To find out more details about the results (and what they mean about when placentals evolved) have a look at my coverage for Nature News.
Written By: Ed Yongcontinue to source article at phenomena.nationalgeographic.com