mammal – Page 2 – Nix Illustration

Spectember/Spectober 2025 #05: Strangels

We’re continuing into Spectober with another anonymous request, this one asking for: “Hominids that evolved with 6 limbs, 2 of which are wings. Limb placement is up to you.”

A digital sketch of a speculative six-limbed hominind, pictured in both tree-climbing and gliding poses. It has a monkey-like face with very large eyes, opposable thumbs and first toes, no tail, short fur over its body – and an extra pair of "arms" hanging just behind its shoulders that end in stubby fingerless hands and support a large gliding membrane. In the aerial pose it's shown grabbing hold of its wing-limbs to hold them in place for gliding.

Living several million years in a possible future, Anomalangelus anthropogenis is a bizarre case of a six-limbed primate.

Its additional pair of upper limbs originate from a heritable form of notomelic polymelia, similar to the Developmental Duplications condition seen in our time’s domestic cattle. It has a rather chimeric genome that appears to contain ancestry from several different hominid lineages, suggesting that this strange little creature actually descends from something that was originally genetically engineered.

It’s a tiny dwarfed species, only about 25cm long (~10″), with a highly arboreal omnivorous loris-like lifestyle, spending most of its life clambering around in trees. Although its extra limbs can’t move independently, lacking a lot of functional musculature and nerve connections, they’ve been exapted into brightly-patterned display structures and also serve as attachment for a large gliding membrane – Anomalangelus uses its forelimbs to grab hold of these “wings” while airborne, spreading them out and stabilizing them to form a composite wing.

Spectember 2025 #04: Kerguelen Kingdom

A couple of anonymous submissions asked for “Kerguelen fauna before it sank 20 million years ago” and “a predator which prowled Cenozoic Kerguelen before it sank”:

[Context: The Kerguelen Plateau is today almost entirely underwater, but during the Cretaceous Period much larger parts were above water as island landmasses. Initially forming during the Gondwanan breakup of what would become Australia, India, and Antarctica, it was eventually left isolated in the forming southern Indian Ocean, and due to long-term volcanic hotspot activity it may have gone through as many as three different periods of rising and sinking before finally almost completely submerging about 20 million years ago.]

In the early Cenozoic, around the time of the Paleocene-Eocene Thermal Maximum, there’s less of Kerguelen’s land above water than there was in the Cretaceous, but the climate is warm-temperate and conifer forests cover the plateau’s islands.

A digital sketch of a speculative descendant of enantiornitheans. It's a large chunky shaggy-feathered flightless bird with a small head, toothed jaws instead of a beak, a long neck, vestigial wings with small claws, thick legs, and a pair of ribbon-like tail feathers that end in wider spaded plumes.

Enantiochen reliquia is a flightless bird standing around 1.5m tall (~5′), and its toothy jaws, wing claws, and ornamental ribbon-like tail plumes on males identify this species as an enantiornithean, descended from a small flighted form that just barely survived through the K-Pg extinction here.

It’s the largest current inhabitant of the Kerguelen plateau, a browsing herbivore filling a similar ecological role to the later moa of Aotearoa.

A digital sketch of a speculative descendant of gondwanatherian mammals. It vaguely resembles a rabbit with small pointed ears, with a deep snout, long digging claws on its digits, a short thin tail, and long hind feet.

Cuniculitherium kerguelensis is another Mesozoic holdover, a gondwanatherian mammal — although a little less unique than Enantiochen since other gondwanatheres still also survive in early Cenozoic South America and Antarctica.

About 40cm long (~1’4″), it’s a rather rabbit-like burrowing herbivore with long hind feet and a fast bounding gait, traits its lineage originally evolved to evade unenlagiine theropods and small terrestrial crocodylomorphs prior to the end-Cretaceous extinction. Those predators are gone from Kerguelen now, but…

A digital sketch of a speculative descendant of australobatrachian frogs. It has a large head, short chunky limbs, and an elongated body with a row of bony amor plates along its spine.

Daptobatrachus archaeotropus is a descendant of australobatrachian frogs. In a case of island gigantism it’s close to the size of a cat, around 50cm long (~1’8″), and with its elongated body, stubby hind legs, and a row of osteoderms down its back, it almost looks like a throwback to the Permian.

Although unable to hop, it’s an ambush predator capable of raising itself up for very brief bursts of crocodile-like galloping, preying on pretty much anything it can potentially fit into its mouth.

Spectember 2025 #01: The Creeping Whale

Another September, another #Spectember, and maybe, just maybe, one day I’ll finally finish getting through the speculative evolution concept submissions you all gave me several years ago.

(Also, a reminder: I’m not taking further requests!)

As with the previous couple of years I’m not setting a definite posting schedule; it’ll just be whatever I can manage to get done during the month.

So, let’s get started with an anonymous submission that requested a “secondarily terrestrial cetacean similar to Cartorhynchus and Sclerocormus”:

A digital sketch of a speculative secondarily-amphibious early whale. It has a short blunt snout with nostrils in front of its large eyes, a humped back, large flippers, a vestigial-looking dorsal fin, and a fluked tail.

Repocetus aigialonatus is a 2.5m long (~8′) Late Oligocene cetacean closely related to mammalodontids — early baleen whales with toothy jaws — living around the mostly-submerged continent of Te Riu-a-Māui Zealandia.

Its ancestors hunted in shallow waters around the low-lying islands, occasionally semi-beaching themselves in pursuit of penguins or to escape from larger marine predators. This eventually led to Repocetus regaining some degree of terrestrial locomotion ability, able to galumph somewhat like modern seals using a combination of undulating its body and pushing off using flippers with powerful shoulder muscles.

It’s slow and awkward, but there are no terrestrial predators to threaten it — and so it’s also reverted to giving birth on the safety of the shore.

Like its mammalodontid relatives it has large eyes and a fairly short snout. It occupies a similar ecological niche to the modern leopard seal, using large sharp teeth to grip and tear at large prey. While it mainly feeds on large fish, it will also use its amphibious abilities to charge onto shore to raid beach-nesting bird colonies or to take advantage of other beached cetaceans.

Notiomastodon

Notiomastodon platensis was a gomphothere – a relative of modern elephants – that lived across much of what is now South America from the mid-Pleistocene to the early Holocene, between about 800,000 and 10,000 years ago.

Similar in size to an Asian elephant, it stood around 2.5m tall at the shoulder (~8’2″) with a domed head and thick tusks that varied in length and curvature between different individuals. It had a stockier build than modern elephants with thicker and slightly shorter limbs, and fossilized footprints suggest it had five nails on its front feet and at least three on the hind feet.

Isotope analysis and wear analysis of Notiomastodon’s teeth suggest it was a generalist browsing herbivore, with different populations adapting their dietary habits to local conditions. As one of the largest South American herbivores of its time it was probably an important seed disperser for plants such as bamboo and palms – and some of the plants that once depended on it may now be “evolutionary anachronisms“.

Protemnodon

Protemnodon viator was a large macropod that lived in what is now western and southern Australia during the late Pleistocene, around 50,000 years ago.

Although it was built more like a giant wallaby, ancient mitochondrial DNA has shown that its closest living relatives are actually modern grey kangaroos.

Estimated to have weighed about 170kg (~375lbs) – twice as much as the largest modern red kangaroos – it would have stood up to 2.4m tall (~8′) on its hind legs. But unlike its living relatives Protemnodon’s limb proportions indicate it wasn’t a very efficient bipedal hopper, instead probably mostly moving with a bounding or galloping quadrupedal gait.

Its forelimb anatomy also suggests it was a good digger, and strongly curved claws on its hind feet may have helped provide grip on uneven ground.

Panochthus

Panochthus tuberculatus was a large glyptodont – a group of giant heavily-armored armadillos – that lived in central and southern South America during the late Pleistocene, about 800,000-12,000 years ago.

Around 3.5m long (~11.5′) and 1.5m tall (~5′), it was similar in size to a modern rhino (or a small car), and its large domed “shell” made up of numerous small bony osteoderms made it resemble a mammalian tortoise. Its skull was short and deep, with ever-growing grinding teeth and downwards-flaring cheekbones that anchored powerful jaw muscles. A preserved hyoid apparatus indicates that Panochthus also had a more flexible tongue than some other glyptodonts.

The base of its tail was segmented into rings that allowed it to flex, while the end of the tail was fused into a solid bony tube that was probably studded with large keratinous knobs or spikes.

While these sort of tail weapons in glyptodonts have been proposed as being anti-predator defenses, biomechanical studies suggest they required precise aiming to be most effective and weren’t well-suited to fending off fast-moving attackers. Instead they may have been more specialized for fighting each other in ritualized forms of combat – an idea supported by injuries in fossil carapaces that appear to have been caused by blows from opponents’ tail clubs.

Dinosorex

Dinosorex, the “terror shrew”, was a genus of eulipotyphlan mammal found across much of Europe for most of the Miocene, ranging from about 23 to 9 million years ago. Part of a family of stem-shrews known as heterosoricids, it was larger than most of its living relatives – probably around 15-20cm long (6-8″) – and inhabited subtropical swampy forest environments.

Dinosorex kaelini here was one of the later species in this lineage, living in what is now Switzerland around 12-10.5 million years ago.

It had massive incisor teeth at the front of its jaws and crushing teeth further back, specialized for grabbing, immobilizing, and cracking open prey like hard-shelled invertebrates. Similar to some modern shrews the tips of these teeth were also reinforced with iron in their enamel, which would have given them a striking dark red coloration.

But while Dinosorex was quite abundant and successful during its time, it seems to have had such a specific ecological preference that it couldn’t adapt when the climate shifted towards the end of the Miocene. Drier conditions and more open savannas quickly took over, and the terror shrews disappeared along with the lush humid forests they were so dependent on.

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.