The Last Placental
55 million years ago, Wyoming.
A small mammal scurries along the tree branches. It is dusk, and it has just left its shelter in the deeper canopy to forage for food. It is an omnivore: it can do a little bit of everything, which is likely how it got to remain alive for so long. But these days, being a jack-of-all-trades isn’t good enough.
This thing looks a bit like the menagerie of ptilodontoideans it shares its habitat with. In fact, you’d be forgiven if you didn’t notice the subtle little hints, like how it chews up and down instead of sliding its jaws from front to back, or its little nails, or its single claw its uses to groom itself. Even as it opens its mouth for a well deserved yawn, you can see large lower premolar teeth: plagiaulacoids, like those of most of the world’s mammals these days.
Yet, it isn’t one of them. The last common ancestors between it and most mammals in its environment lived way back in the Jurassic, when dinosaurs roamed the earth. Though that eagle-like owl nearby is an uncomfortable reminder. Best to watch, dart if it moves.
Where were we? Oh yes.
This animal, Ultimomaia tristis, is the world’s last placental mammal. A carpolestid, to be exact. They were an odd evolutionary experiment; amidst the plethora of eutherians, one lineage lost the epipubic bones omnipresent in Mammalia, and combined with some weird virus genes this allowed for the formation of a complex placenta. Going through long term pregnancies, theirs were the most developed of mammal young, although this little tree climber was born seldomly more complex than the average multituberculate or metatherian joey.
Carpolestids, in particular, weere a branch of a group known as primates, that took to the trees when the forests returned in the aftermath of the KT event. They closely mimicked their contemporary multituberculates in developing plagiaulacoid teeth, well suited to crack open seeds.
In another timeline, these would prosper in the nascent tropical forests of the Eocene, thriving in ways that would alter life on Earth in the most fundamental of ways. Their neighbours would pay the price, blown away by the duststorms of history, to obscurity undignified.
But not here, not in this time. It and its kin were the losers, not so much of a war but a cascade of climatic anf floral events. Their neighbours found the strength to go on, but this chaos was too much for carpolestids, for primates, for Placentalia as a whole.
When the world warmed in the Paleocene/Eocene boundary, that was the last straw. Forests were turned to desert, then back to forest. Seeds grew harder and harder, predatory birds bolder and more cruel. New diseases burned like wildfire, though its likely they were just a single needle in a needle bed.
Carpolestids held on, but they were the only ones to do so. Their neighbours, though affected, came back with a vengeance, now diversifying in an increasingly aggressively competitive hothouse world. And one day there just wasn’t room in this world for even them.
Being an endling is strange. It is a solitary animal, so it doesn’t truly grasp the existential ocean of being alone in all senses of the word. When the dry season gives way to wetter feeding grounds, there is an itch in the loins — the only external ones in the world in fact — and a need for there to be something, someone out there. But unlike the writer, the carpolestid doesn’t need social interactions, just a moment of sex.
Animals are terribly unpicky, for for the ptilodontoideans it shares its habitat with it looks familiar enough. True, the scent, the everything is weird, but that’s irrelevant.
A companion, as related to it as they both are to a platypus, joins it. Sniffing, mounting, leaving.
The endling’s days are numbered, but for now it couldn’t be happier.
***
Welcome to Multituberculate Earth.
