reptile – Nix Illustration

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.

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.)

Hwiccewyrm

Hwiccewyrm trispiculum lived during the late Triassic, around 208-202 million years ago, in what is now England. It was one of the last known members of the procolophonid family, a lineage of small stocky lizard-like animals that had been widespread and abundant earlier in the Triassic.

(Traditionally procolophonids are classified as parareptiles, but some recent studies suggest this group is paraphyletic or polyphyletic, with some “parareptiles” potentially nesting within the diapsids instead.)

Measuring around 30cm long (~1′), Hwiccewyrm had wide flaring cheek bones ornamented with large spines, and like some other procolophonids it may also have had bony scute armor on its body. Its large blunt teeth suggest it was feeding on particularly tough foods such as fibrous vegetation or hard-shelled invertebrates.

Anthracodromeus

Anthracodromeus longipes was an early reptile* that lived in what is now Ohio, USA, during the late Carbonifeorus about 307-305 million years ago.

(*or possibly a very reptile-like stem–amniote)

Around 20cm in total length (~8″), it had a rather lizard-like shape with a long body and a short tail. The digits on all four of its limbs were highly elongated with hooked claws, which appears to have been an adaptation for climbing.

It inhabited a coal forest dominated by lycopsid trees and seed ferns, and as one of the earliest known tetrapods to develop climbing behavior it would have had some ecological advantages over its relatives, being better able to escape from predators and access new food sources.

Schoenesmahl

Schoenesmahl dyspepsia was a lizard that lived in what is now Europe during the late Jurassic, about 150 million years ago. Around 30cm long (~1′), it had a fairly small head, elongated hind limbs, and a very long tail – proportions that suggest it was an agile animal capable of fast running.

Only one specimen is known, most notable for being preserved inside the stomach of the dinosaur Compsognathus. For a long time it was classified as an example of Bavarisaurus, but it was finally recognized as representing a distinct type of lizard in 2018, with recent studies placing it as an early member of the gecko lineage closely related to ardeosaurids and eichstaettisaurids.

Unguinychus

Drepanosaurs were a weird little group of tree-climbing Triassic reptiles with prehensile claw-tipped tails, chameleon-like bodies, humped backs, grasping feet, long necks, and somewhat bird-like skulls that may have been tipped with toothless beaks in some species.

Recently some of them have been recognized as also having adaptations for digging and ripping into insect nests, similar to modern anteaters, with highly specialized forelimb bones and a massively enlarged hoked claw on each hand.

And now we have another one of these digging drepanosaurs: Unguinychus onyx, whose name delightfully translates to “claw claw claw”!

Living in what is now New Mexico, USA during the late Triassic, around 215-208 million years ago, Unguinychus is only known from its enlarged hand claws but was probably similar in size to some of its close relatives, likely around 40cm long (~1’4″).

Based on skin impressions from the early drepanosaur Kyrgyzsaurus it also would have been covered in small scales, possibly with a skin crest and a chameleon-like throat sac.

Drepanosaurs’ evolutionary relationships are rather unclear, with various studies classifying them as an early branch of diapsid reptiles, as close relatives of the gliding kuehneosaurids, or as protorosaurian archosauromorphs. But recently another idea has been proposed, instead placing them slightly further up the archosauromorph evolutionary tree in the allokotosaur lineage close to trilophosaurids – and notably making them very closely related to fellow Triassic bird-headed weirdo Teraterpeton.

Jiangxichelys neimongolensis

Jiangxichelys neimongolensis was a terrestrial turtle that was part of an extinct group known as nanhsiungchelyids, whose closest living relatives today are the aquatic softshell turtles.

(This species was previously known as “Zangerlia” neimongolensis, but has since been moved into the genus Jiangxichelys instead.)

It lived towards the end of the Cretaceous, about 75-71 million years ago, in what is now the Gobi Desert – which at the time was more of a semi-arid climate with both rivers and sand dunes.

Its 60cm long (~2′) carapace had a long wide shape that made it appear rather flattened from the front, but not to quite as much an extreme as its larger American cousin Basilemys.

Several fairly well-preserved specimens have been found that appear to have been buried alive, probably either engulfed by sudden sandstorms or trapped in collapsing burrows. This has preserved some anatomical details previously unknown in nanhsiungchelyids, such as the pattern of scales on top of the head and the presence of large bony osteoderms on the underside of the front toes, which may have aided with traction on loose sandy ground.

Dinocephalosaurus

Dinocephalosaurus orientalis was a fully aquatic protorosaur reptile living in what is now southwest China during the mid-Triassic, about 244 million years ago.

Up to 6m long (~19’8″), it had a long serpentine body with paddle-like limbs and an especially elongated neck – but despite the superficial similarities to its semi-aquatic cousin Tanystropheus, Dinocephalosaurus’ long neck appears to have been independently evolved.

Much like the similarly-shaped elasmosaurs, its neck may have had a “stealth” function, allowing it to bring its jaws closer to targets before the rest of its body was visible, then using side-to-side snapping bites to catch its prey in its interlocking “fish-trap” teeth.

A preserved well-developed embryo inside one specimen also suggests that Dinocephalosaurus gave birth to live young, making it one of only two archosauromorph lineages known to have ever evolved this reproductive strategy.

Megapterygius

Most mosasaurs all had very similar body plans: they were streamlined scaly monitor-lizard-like marine reptiles with four rounded paddle-shaped flippers, and many of them also had large shark-like tail fins.

But Megapterygius wakayamaensis here seems to have been doing something a bit different.

Living towards the end of the Cretaceous, about 72 million years ago, in the waters covering what is now western Japan, this mosasaur was around the size of a modern orca, roughly 6m long (~20′).

Unlike other known mosasaurs its flippers were huge, bigger than its own head and distinctively wing-shaped, with the back pair being larger than the front. This is an arrangement oddly reminiscent of the unrelated plesiosaurs, and may suggest a convergent sort of highly maneuverable “underwater flight” swimming ability – but unlike plesiosaurs Megapterygius also still had a powerful fluked tail, so how exactly all of its fins worked together is still unknown.

It’s also the first mosasaur known to preserve potential evidence of a dorsal fin. Some of its back vertebrae show a change in orientation at the point where a fin base would be expected to be, closely resembling the vertebrae shape of cetaceans like the modern harbor porpoise.

Lewisuchus

Last week I mentioned the one oddball dinosauriform that had crocodilian-like osteoderm armor, so let’s take a look at that one too.

Lewisuchus admixtus lived in what is now northwest Argentina during the late Triassic, around 236-234 million years ago. About 1m long (3’3″), it was an early member of the silesaurids – a group of dinosauriforms that weren’t quite dinosaurs themselves, but were very closely related to the earliest true dinosaurs.

(They’ve also been proposed as instead being early ornithisichians, but we’re not getting into that today.)

Much like its later silesaurid relatives Lewisuchus had a long neck and slender limbs, and was probably mainly quadrupedal, possibly with the ability to briefly run bipedally to escape from threats. Its serrated teeth suggest it was carnivorous, likely feeding on both smaller vertebrates and the abundant insects found in the same fossil beds.

Uniquely for an early dinosauriform it also had a single row of bony osteoderms running along its spine. Although it lived at close to the same time as the similarly-armored Mambachiton their last common ancestor was at least 10 million years earlier, and no other early dinosaur precursors with osteoderms are currently known – so this was probably a case of Lewisuchus independently re-evolving the same sort of feature.