It seems like every other week paleontologists in China are finding new fossils that change our understanding of evolutionary lineages. This week it’s come to light that a new mammalian fossil had been found in China that dates to 160 million-years-old. It’s been named Juramaia sinensis, which means ‘Jurassic mother from China’, and is 35 million years older than the previously oldest known mammalian fossil, Eomaia (dated to 125 million years old).
It’s shrew-like in form, and part of the placental-mammal lineage and is thus a eutherian just like ourselves. So this species may be a direct ancestor of ours, or else a close cousin of our direct ancestors.
There are two other mammalian lineages, monotremes such as platypus and echidnas (lay eggs), and marsupials such as possums and kangaroos (have pouches). Though it’s still a little unclear, it’s suggested that monotremes split off on their own lineage around 170 million years ago, with eutherians splitting off from marsupials more recently.
The fossil has forepaws adapted to an arboreal life, that is one spent climbing trees, and would’ve spent its time in Jurassic forests chasing down small insects and other animals at night. Such a diet doesn’t get you to a huge size, and these guys would’ve reached ~15g. What a beast!