@poshtearexdoodles asked for “African wild dogs evolved to fill the larger pack animal niche of lions”:
Although in this particular timeline the endangered and fragmented wild painted dogs in Africa didn’t survive far past modern times, that wasn’t the final extinction of the species – captive groups persisted, and after the [REDACTED] of humans an escaped population managed to carve out a niche for themselves in the grasslands of southern North America.
Their most notable descendant is Megainolycos poshtearexi. At nearly 1m tall at the shoulder (~3’3″) it’s one of the largest canids to ever exist, comparable to present-day lions in size and general ecology, with short thick bone-crushing jaws convergent with those of hyenas.
It also retains the complex variable coat coloration of its ancestors, with each individual having a unique disruptive pattern of black, white, and brown blotches.
Much like its ancestors it’s a highly social pack predator specialized for endurance hunting. Along with some surprisingly horse-like limb ligament morphology, its feet now sport hoof-like nails rather than claws, and it pursues prey over long distances to the point of exhaustion – mainly targeting the larger ungulates across its prairie habitat such as hogs, horses, bovids, and deer.
Roy (@roygattero) requested “ratel becoming the new african big predator”:
Perforictis royi is the latest in the long and venerable tradition of various synapsid lineages discovering the ecological niche of “big stabby saber-teeth“.
A descendant of the modern ratel/honey badger, it stands around 80cm tall at the shoulder (~2’8″), and convergently resembles the feline-like build of some of its more ancientrelatives. Inhabiting the tropical forests of the rifted-off island continent of East Africa, it’s an ambush predator specializing in tackling larger prey – primarily ungulates and primates, but also occasionally giant rodents and hyraxes.
Usually cooperatively hunting in mated pairs, these mustelids stalk close to their targets before attacking, with one individual focusing on toppling and immobilizing their target while the other positions itself to deliver a swift precision killing bite to the throat with its saber-teeth and powerful neck musculature.
Perforictis scent marks its territory using extremely pungent secretions from its anal pouch rubbed onto vegatation, along with making loud scream-like vocalizations.
Descended from an arboreal offshoot lineage of the modern least weasel, Maximagale gaycooniei is a bizarre mustelid that appears to have converged on the lifestyle of ambush-hunting tree snakes, evolving in northern latitudes where actual snakes are largely absent.
Growing to about 1m long (3’3″), it’s not truly legless but its limbs are all reduced down to tiny vestigial single-clawed spurs, which are used to help anchor its body while climbing and as claspers during mating. It moves around with a distinctive inchworm-like looping gait, alternating grasping and releasing with its front and hind spurs.
Its build is bottom-heavy, with most of its mass concentrated in its thicker back end, and its tail is semi-prehensile. It clings to trees with its body bunched up, camouflaged with cryptic coloration, and rapidly whips its long flexible front half out to snap its powerfully-muscled jaws at prey – such as insects, birds, lizards, frogs, small mammals, and pretty much anything else that comes within its reach.
It will also opportunistically raid the nest of birds and arboreal mammals.
Due to the less frequent meals its ambush-hunting tactics provide, it has a much slower metabolism than its ancestors, and it conserves energy with daily periods of torpor and longer hibernation during the colder months of winter. It has also retained its ancestor’s tendency to seasonally shrink its brain size to reduce energy requirements even more.
It’s September, it’s #Spectember, and I’m still plugging away at that big ol’ pile of speculative evolution idea submissions from a few years ago.
I will never be free.
Much like last year I’m not setting a definite posting schedule for this month; it’ll just be whenever and whatever I can manage to get done.
(Also, a reminder: I’m still not currently taking new requests!)
So let’s get started with an anonymous submission that requested a “swimming piscivorous canid”:
Descended from the short-eared dog (a species that in modern times already has partially-webbed paws and eats a large proportion of fish in its diet), Pelagicyon salsus is a 2m long (~6’6″) semi-aquatic piscivorous canid with a stocky body, short webbed limbs, and a long flattened tail.
The back of its skull is very wide, anchoring its thick neck musculature and accommodating huge cheekbones with powerful jaw muscles, but in contrast its snout is elongated and slender – a combination of features that allows it to sweep its toothy jaws through the water to rapidly snap at fish in a similar manner to gharials.
Most other members of its lineage inhabit freshwater rivers and swamps, but Pelagicyon is an unusual marine offshoot that has developed enough salt tolerance to swim, feed, and even drink exclusively in seawater.
Rostrorutellum admantusi is descended from small cetotheres that became isolated in a large inland body of water (similar to the modern Caspian Sea), eventually becoming landlocked and gradually reducing in salinity towards fully freshwater.
Highly dwarfed in size, just 2-3m long (~6’6″-9’10”), they’re slow swimmers with broad duck-like snouts that are used to scoop up mouthfuls of sediment and strain out their invertebrate prey in a similar feeding style to gray whales.
Due to the murkiness of the water, and the lack of large predators in their environment, they have poor eyesight and instead use sensory bristles and electroreceptors around their snouts to navigate and detect prey.
And an anonymous submission requested a “whale-like filter-feeding marine crocodile”:
Sestrosuchus aigialus is a 6m long (~20′) crocodilian closely related to the modern American crocodile, living in warm shallow coastal waters.
It’s adapted for an almost fully aquatic lifestyle convergently similar to the ancient thalattosuchians, swimming with undulations of its long tail and steering with flipper-like limbs. But unlike other crocs it’s specialized for filter-feeding, with numerous delicate needle-like teeth in its jaws that interlock to sieve out small fish and planktonic invertebrates from the water.
A couple more suggestions also asked for “fully aquatic pinnipeds” and “future crabeater seal evolution”:
Euphausiolethrus volucer is a fully aquatic descendant of the crabeater seal. About 5m long (~16’4″), it occupies the ecological niche of a small baleen whale in the krill-abundant Antarctic waters that lack most actual baleen whales.
Its jaws contain numerous finely-lobed teeth that are used to strain krill from the water, and it utilizes all four of its wing-like flippers to swim in an “underwater flight” motion similar to that of plesiosaurs.
Highly social, it tends to congregate in pods that cooperate to herd swarms of krill for easier feeding.
Most modern meat-eating placental mammals are carnivorans, a group that contains two distinct lineages: the feliforms (cats, hyenas, mongooses, viverrids, civets, linsangs, and euplerids) and the caniforms (dogs, bears, seals, raccoons, and mustelids).
The closest living relatives of these animals are pangolins, and their last common ancestor probably lived sometime between the Late Cretaceous and early Paleocene. But the actual early evolutionary history of the carnivorans themselves is rather murkier.
The earliest known carnivoran-like forms – known as carnivoramorphs – all looked vaguely-genet-like and were an ecologically diverse bunch of small predators, ranging from weasel-sized tree-climbers to fox-sized ground-based hunters, found all across North America and Eurasia during the Paleocene and Eocene. They lacked most of the anatomical specializations of true carnivorans, and didn’t quite fit into either the feliforms or caniforms, but their distinctive carnassial teeth make it obvious they were still very closely related.
From their initial discovery in the late 19th century, through to the late 20th century, these carnivoramorphs were traditionally all lumped together under the name “miacids“. As a result the group quickly turned into a big wastebasket taxon of similar-looking animals, all united more by just not being true carnivorans than by any shared characteristics between themselves.
Miacis parvivorus
But during the last couple of decades this mess has finally started to get cleared up. One distinct lineage of miacid-like animals called viverravids were split off, now thought to be the one of very earliest branches of the carnivoramorph evolutionary tree. Several other “miacids” have also been reassessed and renamed, reclassified as falling into various points in an evolutionary grade between viverravids and true carnivorans, and a coupleof species even turned out to actually be caniforms.
The true carnivorans arose from somewhere within the “miacids” during the mid-Eocene, but it’s still unclear where exactly to draw the taxonomic line between them. Forms like Quercygale and Tapocyon might be very close to the ancestral carnivoran – but they might instead be early feliforms – and some studies have also proposed that nimravids (“false sabertooth cats”) may actually be “advanced” carnivoramorphs instead of early feliforms.
There are also quite a few remaining “miacids” that still need sorting out, especially in the genus Miacis. There have to be other distinct lineages of these carnivoramorphs still hidden in the remaining wastebasket pile, and if we can eventually distinguish them from each other it might help to make early carnivoran relationships a bit clearer.
Desmatophocids were a group of seal-like pinnipeds that appeared very early in the group’s evolution, around 23 million years ago. They were found across the northern Pacific from the west coast of North America to Japan, and were the first pinnipeds to get big, with some species reaching sizes comparable to modern northern elephant seals.
They had a mixture of anatomical features similar to true seals, sea lions, and walruses, but weren’t actually the ancestors of any of those modern groups. Instead they seem to have just been their own separate thing, a very early diverging “cousin” lineage of pinnipeds that convergently developed close resemblances to their later relatives.
Allodesmus demerei here was one of the last known desmatophocids, living in the late Miocene (~9 million years ago) in what is now southwest Washington, USA.
It would have been a sea lion-like animal, able to walk on all fours when hauled out on land, and showed distinct sexual dimorphism, with males growing to sizes of around 4m long (13′) and females being somewhat smaller. It powered its swimming using its front flippers, and may have mostly foraged in deep dark waters, using both keen vision and sensitive whiskers to locate prey.
The nasal region of its skull also shows some similarities to modern elephant seals, and some reconstructions depict males with the same sort of large proboscis.
