I have been fascinated by the fact that evolution tells us that if we could journey back in time, then all of our ancestors start to merge, with some surprising results. I wrote a series of posts exploring this topic some years ago and pointed out some surprising (to me at least) results.
It turns that we only needed to go back as far as 50 CE or so to find that everyone on Earth right now had at least one common ancestor and that if we go back to around 2,000 BCE then everyone who lived then (and whose line didn’t die out entirely) are the common ancestors of everyone who lives now. In other words, all of us living today had the identical set of ancestors who lived as recently as 4,000 years ago,.
But you can go back even further and then you find that entire species start merging with other species to have a common ancestor and at some point, on the way to the final destination of the common ancestor of every living organism, you will arrive at the common ancestor of all the mammals.
It has long been thought that the common ancestor of mammals, that came into its own after the dinosaurs were killed off by the asteroid or comet that collided with the Earth about 66 million years ago was a small shrew-like creature.
Ed Yong points to new paper that uses DNA of the species living today to try and construct a more reliable picture of what that ancestor might have looked like and they come up witht something that would look like the animal in the picture on the right.
The critter turned out to be a tree-climbing, furry-tailed insect eater that weighed between 6 and 245 grams. It gave birth to blind, hairless young, one at a time. Its brain was highly folded, and it had three pairs of molars on each jaw.
The researchers analysed more than 4,500 anatomical traits — almost ten times as many as any previous study. These included traits from 86 living and extinct mammals.
The analysis, which is published in Science, confirms that the placentals diversified a few hundred thousand years after the (non-avian) dinosaurs went extinct, so groups such as rodents and primates never shared the planet with the prehistoric reptiles. This conclusion is backed up by the fact that no one has ever found fossils of placental mammals from before the extinction of the dinosaurs 65 million years ago — but it contradicts genetic studies that put the group’s origin at around 100 million years ago.
This creature must have been around after the supercontinent of Gondwana split into today’s southern land masses, so its descendants must have swum or otherwise travelled over long distances to explain the wide distribution of placentals today.
So say hello to our great-great-great-…-great-grandparent.