Meet the Ancestor of Every Human, Bat, Cat, Whale and Mouse


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 Yong
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  1. Wait a minute… wait a minute… waitaminute dammit! This thing does not look like me at all! What about baby Jesus? What about the BIBLE? What about Adam, and that chick of his, and the rib thing and a 6000 year-old earth and all that scared… I mean sacred knowledge? Are you seriously telling me my grandpa came from this thing? Get REAL people. Do some serious research for a change. How do people get to publish these fairy stories?

  2. eek, it’s a rat!

    Hang on though, how could we have evolved from a rat when there are still rats around today? Gotcha!

    Seriously, I would also love to learn more about the ancestry of this early mammal, to see how the mammalian characteristics evolved, and over what timescale.

  3. At last a “transitional form” has been found!

    Oh! Wait! Loads of them have already been found, its just ignorant people who think none have, even when they see them

  4. There is another take on this story here:-
    Researchers recorded observational traits for 86 placental mammal species, including 40 fossil species. The resulting database contains more than 12,000 images that correspond to more than 4,500 traits detailing characteristics like the presence or absence of wings, teeth and certain bones, type of hair cover and brain structures.

    The team reconstructed the anatomy of the common ancestor by mapping the traits most strongly supported by the data. These suggest a two-horned uterus, a brain with a convoluted cerebral cortex and a placenta in which maternal blood came in close contact with membranes surrounding the fetus, as in humans.

    In the past, the evolutionary history of placental mammals has been interpreted in very different ways, depending on what data the researchers focus on. One leading analysis, based on genomic data alone, suggests that a number of placental mammal lineages existed in the Late Cretaceous and survived the Cretaceous-Paleogene extinction.

    “It has been suggested that primates diverged from other mammals well before the extinction of the dinosaurs, but our work using direct evidence from the fossil record tells a different story,” says Bloch.


  5. N_Ellis 6 –
    At last a “transitional form” has been found!

    And possibly living ones which are in continuous “transition” too!

    Modern tree shrews closely resemble this ancestor: .. …

    Alt Text (Right click and select “view image”)

    The treeshrews (or tree shrews or banxrings[2]) are small mammals native to the tropical forests of Southeast Asia. They make up the families Tupaiidae, the treeshrews, and Ptilocercidae, the pen-tailed treeshrews, and the entire order Scandentia. There are 20 species in 5 genera. Treeshrews have a higher brain to body mass ratio than any other mammals, including humans,[3] though high ratios are not uncommon for animals weighing less than a kilogram.

    Although called treeshrews, they are not true shrews (although they were previously classified in the Insectivora), and not all species are necessarily arboreal. Among other things, they eat Rafflesia fruit.

    Among orders of mammals, treeshrews are closely related to primates, and have been used as an alternative to primates in experimental studies –

  6. It’s incredible that a 1.5g mammal like the bumblebee bat can maintain an even body temp. You’d think there’d be some minimum body mass required to provide sufficient thermal inertia.

    As for these ancestral mammals, they look identical to the possums running all over my roof tiles last night. Makes one appreciate evolution all the more as dinosaurs on the roof would probably create more disturbance.

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