mammal – Nix Illustration

Incamys

Incamys bolivianus was a caviomorph rodent representing an early member of the chinchillid family, with its closest modern relatives being chinchillas and viscachas.

Living in what is now Bolivia and Argentina during the late Oligocene about 27 million years ago, it inhabited an arid open grassland at a time when the area’s climate had drastically cooled due to the formation of the Antarctic Circumpolar Current.

It’s estimated to have been similar in size to a large modern chinchilla – weighing around 700g (~1lb 8oz) and measuring about 25-30cm long not including the tail (~10-12″).

An endocast of the shape of its brain from a near-complete fossil skull shows that it had a well-developed sense of hearing, particularly in vocalization processing, suggesting it may have been a social animal living in groups communicating with complex calls similar to modern chinchillids. It was probably a ground-dweller less agile than its modern relatives, but still capable of fast movements.

Hassianycteris

Hassianycteris messelensis was an early bat that lived in what is now Germany during the mid-Eocene, about 47 million years ago.

It’s generally considered to be very closely related to the common ancestry of modern bats – but a recent study suggests that the stem-bat evolutionary tree is actually quite a bit more complicated than previously thought.

It had a 35-40cm wingspan (~14″-16″), and thanks to the exceptional preservation of the Messel Pit fossil site we actually know some details about its external life appearance. One specimen preserves a soft-tissue impression of its ear shape, and fossilized melanosomes suggest that its fur was colored reddish-brown.

Its wing proportions indicate it was adapted to fly high and fast in open spaces, and its strong jaws and preserved gut contents show it mainly preyed on tough-shelled insects like beetles.

Miosiren

Miosiren kocki was a sirenian (sea cow) that lived during the early Miocene (~20-15 million years ago) in what is now the North Sea basin in northwestern Europe.

Similar in size to the very largest modern manatees, about 4-4.5m long (~13-14’10”), it has traditionally been classified as an early member of the manatee lineage – but a study in 2022 suggested it may instead represent a much earlier stem of the sirenian evolutionary tree, with its ancestors potentially having diverged around 34 million years ago.

It had unusually thickened bones in its skull, especially around the roof of its mouth, which would have given its jaws a very strong chewing force. Isotope analysis of its teeth show it was part of a marine algae-based food web, unlike the seagrass-based diets of other sirenians, so it may have been specialized to feed on a much tougher diet. Possibly it was eating something like calcareous algae, or more speculatively it might even have been crunching on hard-shelled algae-consuming marine invertebrates.

Eons Roundup 15

It’s time for a little bit more recent PBS Eons work this week:

An illustration of Arctodictis, an extinct predatory mammal related to modern marsupials. It's a vaguely wolverine-like animal with a boxy snout, a low-slung body, stout limbs, and a long tail. It's depicted in a crouched stalking pose, and it's colored grey-brown with darker spot and stripe markings. — Arctodictis sp.

An illustration of Thoatherium, an extinct hoofed mammal. It resembles a small horse or deer, with a long face, high-set pointed ears, a boxy body, a short tail, and long slender legs each ending in a single hoofed toe. It's depicted with its head lowered to browse on some leaves, and it's colored reddish-brown with a darker back and limbs and a lighter belly — Arctodictis sp.

• The metatherian predator Arctodictis and the litoptern ungulate Thoatherium from “The Mystery of South America’s False Horses”

Albireo

Albireonids were an early branch of the delphinoid whales, with their closest living relatives being modern oceanic dolphins, narwhals and belugas, and porpoises. Known from temperate latitudes of the North Pacific Ocean between the late Miocene and the late Pliocene, about 9-2.5 million years ago, their fossil remains are very rare in coastal deposits and they seem to have primarily been offshore open ocean animals.

Albireo whistleri is the best known member of this family, represented by a near-complete skeleton from what is now Isla de Cedros in Baja California, Mexico, dating to the late Miocene between about 8 and 6 million years ago. It was a rather small dolphin, around 2.5m long (~8’2″), with a stocky body, fairly broad flippers, and skull anatomy with some convergent similarities with the modern Dall’s porpoise.

Interestingly these dolphins also seem to have frequently had pathological neck vertebrae, with both Albireo whisteri and the younger species Albireo savagei from California, USA, showing unusually asymmetrical atlas bones – but on opposite sides to each other. This might be due to illness or injury earlier in life, or possibly be evidence of some sort of “handedness” with individuals preferring to perform some actions more with one side of their body than the other.

Romaleodelphis

Romaleodelphis pollerspoecki was a dolphin-like toothed whale related to the ancestors of both modern oceanic dolphins and beaked whales, living in coastal waters covering what is now Austria during the early Miocene about 22 million years ago.

Although only known from a single fossil skull, this cetacean was probably around 3m long (~9’10”). It had a long snout lined with over 100 small pointed uniformly-shaped teeth, and the bony walls of its inner ears were well-preserved enough to show that it was able to hear narrow-band high frequency sounds – a specific form of echolocation that has convergently evolved multiple times in various modern and extinct toothed whale lineages.

Based on the presence of ancient river-mouth deposits in the area where Romaleodelphis was found, it may potentially have been capable of traversing between marine, brackish, and freshwater environments similar to the modern franciscana.

Spectember/Spectober 2024 #10: Nosey Sea Monkey & Louse Mouse

Okay, let’s finish up this year’s round of speculative evolution concepts with one last post before we get back to normal paleoart content.

~~(…what do you mean it’s November 3rd? how did that happen?)~~

Belial Lyka asked for a “marine proboscis monkey with a somewhat buoyant nose”:

A shaded sketch of a speculative semiaquatic descendant of proboscis monkeys. It has a large trunk-like nose, a fat body, long arms ending in flipper-like hands, short legs with webbed feet, and a short thick tail. A second image shows its head with its nose inflated into a balloon-like display structure.

A descendant of modern proboscis monkeys, Phusarhinus beliallykae is a large semiaquatic primate found in shallow marshy coastal areas of what was once Southeast Asia. Around 4m long (~13′) it has a lifestyle somewhat similar to ancient early sirenians, feeding on soft aquatic plants and hauling out onto land to rest.

Its dense rib bones and long flipper-like grasping forelimbs make it rather front-heavy, allowing it to naturally float with its head and arms hanging down closer to the bottom for energy-efficient foraging. When it needs to resurface to breathe it shunts air from its lungs into its large inflatable nasal sacs, altering its buoyancy enough to tip its head back up towards the surface.

Unlike its ancestors the elaborate nasal structures are found on both males and females – although they’re more brightly colored in males and are also used for visual courtship displays and as resonating chambers for loud booming calls.

And somebody who only gave their name as “bunny” suggested a “parasitic rodent”:

A shaded sketch of a speculative parasitic descendant of semiaquatic rats. It has a wide flattened body with thick armor-like bands running down its back, a small head, stubby limbs tipped with long hooked claws, and a short fat tail.

Sanguichelonamys bunnyi is a highly unusual descendant of a rakali-like semiaquatic rodent that had a symbiotic relationship with early members of the Phusarhinus lineage. The rodents initially just removed algae and external parasites from the bodies of the increasingly bulky aquatic monkeys, but things have recently started to turn more parasitic.

At just 3cm long (~1.2″) Sanguichelonamys is one of the smallest mammals to ever exist, with a wide flattened body and sharp hooked claws used to cling onto its host monkey’s thick skin. Although it still does remove other parasites, during haul-out periods it will also use its sharp incisors to deliberately enlarge the wounds left behind – or even open up new ones – and directly feed on fresh blood from its host.

The thickened keratinous skin along its head and back has a specialized hydrophobic surface that traps a layer of air while underwater, acting as a “rebreather” bubble similar to that of water anoles. Along with the ability to drastically slow down its metabolism and respiration rate, this allows Sanguichelonamys to survive being submerged during its host’s lengthy foraging dives.

Spectember/Spectober 2024 #09: Big Bad Wild Dogs

@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.

A shaded sketch of a speculative descendant of painted dogs. It's a large wolf-like animal with short thick hyena-like jaws, a mottled shaggy coat of fur, and and small hoof-like nails on its feet.

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.

Spectember/Spectober 2024 #08: Saberatel

Roy (@roygattero) requested “ratel becoming the new african big predator”:

A shaded sketch of a speculative descendant of honey badgers. It's a somewhat cat-like animal with a short snout, long saber-teeth, small ears, semi-digitigrade limbs, a mottled coat, and a short tail.

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 ancient relatives. 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.

Spectember 2024 #05: Most Weasel

GayCoonie suggested a “future legless mustelid”:

A shaded sketch of the head of a speculative descendant of the least weasel, shown in both side view and bunched up clinging to a branch. It's a very elongated animal with no obvious limbs, having just small hooked spurs where its legs should be. It has a small weasel-like head with front-facing eyes and small ears, a long neck, a long slender chest and torso, and a thicker fatter back end with a tapering semi-prehensile tail.

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.