Nix Illustration – Page 5 – Paleontology and science illustration

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.

Akidostropheus

Akidostropheus oligos was a small tanystropheid archosauromorph reptile that lived during the late Triassic, about 223-218 million years ago, in what is now Arizona, USA.

Only a few tiny isolated vertebrae have been discovered, so its full size and appearance isn’t known – making any reconstruction rather speculative – but it was probably around 30cm long (~12″). Like other tanystropheids it would have been a long-necked lizard-like animal, and may have had a similar build to the closely-related Tanytrachelos.

But despite the scarcity of material the few known vertebrae are unique among archosauromorphs, bearing elongated spikes with a surface texture that suggests they were covered with keratinous sheaths. The spikes were conical, sharp, and hooked on the neck and upper back, but became more flattened, straighter, and blade-like on the lower back and tail.

These structures were probably defensive in nature, especially considering that there’s direct fossil evidence for predators targeting the long necks of tanystropheids and decaptiating them.

Akidostropheus lived in a tropical floodplain environment around a meandering river system, but without more and better fossils it’s impossible to tell what its ecology was. Tanystropheids were a strange and diverse bunch, with both terrestrial and aquatic lifestyles, bipedal runners, and possibly even bizarre leg-gliders, so this spiky little Triassic weirdo could have been doing almost anything.

Gigantspinosaurus

Gigantspinosaurus sichuanensis was an early stegosaur that lived during the mid-Jurassic, about 166 million years ago, in what is now southwestern China.

Around 4.5m long (~14’9″), it had relatively small back plates and a pair of enormous shoulder spikes. It’s unclear exactly how the shoulder spines were positioned in life, but based on how they were found articulated in a fairly complete skeleton they seem to have swept sideways and backwards, protecting Gigantspinosaurus’ flanks.

Skin impressions show a mosaic of polygonal scales with scattered “rosettes” made up of larger scales surrounded by a ring of smaller scales, with a rough ridged surface texture that may have reduced light glare – suggesting an overall more matte appearance rather than glossy.

The thigh bones of one specimen are pathological, showing evidence that these dinosaurs sometimes suffered from bone tumors.

Tulaneia

Tulaneia amabilia was an enigmatic Ediacaran animal that lived in what is now Nevada, USA just before the start of the Cambrian Period, about 540 million years ago.

Up to around 10cm across (~4″), its body was made up of a fan-shaped frill of airbed-like tubes, with tips that separated from each other and tapered to blunt points. Much like its close relative Ernietta it would have lived with its base buried in the seafloor sediment, and it was probably a suspension feeder catching organic particles in water currents.

One Tulaneia fossil specimen shows birfurcating tips, but it’s unclear whether this was a common feature of this species or a developmental anomaly in this particular individual.

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“.

Mirasaura

Back in 1939, fossil collector Louis Grauvogel discovered a couple of reptile fossils in Middle Triassic-aged deposits (~247 million years old) in eastern France. A large preserved structure was noted above the animal’s back, but for many years it was interpreted as an unrelated fish fin, insect wing, or plant frond.

It was only when the State Museum of Natural History Stuttgart acquired the specimens in 2019 that they were recognized as representing something very special: a long-sought-after relative of the bizarre and enigmatic Longisquama!

Mirasaura grauvogeli grew to around 30cm long (~1′) and was, if anything, even stranger than its relative. It had humped shoulders, grasping limbs, and a bird-like head with large forward-facing eyes and a long pointed snout that was toothless at the front, probably used to probe for small invertebrates in cracks and crevices.

But most strikingly it had up to 20 tall structures overlapping along its back to form a sail-like crest. Although they were superficially feather-like in shape with preserved melanosomes that resemble those of birds, structurally they weren’t feathers at all – but they also weren’t modified scales. Instead these appear to have been an entirely novel type of skin appendage, made up of continuous sheets with a midline shaft and a corrugated texture.

The crest was probably used for visual display, and 80 additional fossils of isolated crest structures suggest they were regularly shed and regrown.

Along with Longisquama, Mirasaura appears to have been an early member of the drepanosaur lineage – a group of wonderfully weird tamandua-like reptiles whose evolutionary relationships are still disputed, with different studies currently recovering them as either a unique early offshoot of the diapsids or as archosauromorphs.

(Interestingly, a specimen of Drepanosaurus reportedly preserves some soft tissue on its back that may also be one of these strange new crest structures. Drepanosaurs just keep on getting weirder and weirder and I love them.)

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.

Sinopterus

Sinopterus dongi was a tapejarid pterosaur that lived during the early Cretaceous, around 120 million years ago, in a temperate forest in what is now northeastern China.

It’s known from multiple specimens representing different life stages, with the largest fully mature individuals reaching a wingspan of about 1.9m (6’2″). Like other tapejarids it had a toothless parrot-like beak, and a low bony crest on its skull may have supported a larger soft-tissue structure.

A specimen with gut contents has been found showing evidence of plant matter and gastroliths, suggesting that Sinopterus was primarily herbivorous.

Marmorerpeton

Marmorerpeton wakei was an early salamander that lived during the mid-Jurassic, about 166 million years ago, in coastal lakes and rivers covering what is now the Isle of Skye, Scotland.

Growing to around 40cm long (~1’4″), it had a wide shallow skull with strong jaws similar to those of modern giant salamanders, suggesting it had a convergently similar sort of sit-and-wait ambush predator lifestyle – using suction feeding to pull prey into its mouth, then powerful bites to subdue it.

Although its body was fairly robustly built its anatomy was somewhat neotenic, retaining some late-stage larval features and staying fully aquatic into adulthood.

Poposaurus

Despite its incredible resemblance to theropod dinosaurs, Poposaurus gracilis was actually a pseudosuchian more closely related to crocodilians than to dinosaurs.

Living in what is now North America during the Late Triassic, about 237-216 million years ago, Poposaurus grew to around 4.5m long (~15′) with roughly half of that length taken up by just its long tail. With its sharp-toothed jaws, small arms, bipedal locomotion, and counterbalancing tail, it convergently evolved the same sort of body plan and ecology as carnivorous theropods – which were still in their early days at the time, and wouldn’t really become the dominant terrestrial predators until after the end-Triassic extinction.

Unlike most other pseudosuchians Poposaurus lacked bony osteoderm armor, seems to have been capable of a digitigrade posture, and its claws were flattened and somewhat hoof-like, all adaptations that suggest it was built for running after fast-moving prey.