triassic weirdos – 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.)

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.

Panacanthocaris

Panacanthocaris ketmenica* here was a member of an extinct group of crustaceans known as kazacharthrans – close relatives of modern tadpole shrimp known mainly from Central Asia during the mid-to-late Triassic (but with possible German relatives from both the late Triassic and further back in the late Paleozoic).

Fossils of Panacanthocaris have been found in Kazakhstan and northwest China, dating to about 235-221 million years ago. It was fairly big compared to most of its modern cousins, reaching at least 10cm in length (~4″), and had distinctive spines around the edges of its carapace and its telson.

It’s not clear if it had eyes – there’s a single opening near the front of its carapace that may have housed some, and so I’ve depicted it here with just one naupliar eye similar to the “third eye” of tadpole shrimp.

It probably had a fairly similar lifestyle to its modern relatives, living in shallow freshwater and temporary pools and opportunistically feeding on everything from algae to smaller aquatic animals.

(* Sometimes also called P. ketmenia. May also be the same thing as Iliella spinosa, but until that paper is officially published the current name still stands.)

Hupehsuchus

Hupehsuchians were small marine reptiles closely related to ichthyosaurs, known only from the Early Triassic of southwestern China about 249-247 million years ago. They had toothless snouts, streamlined bodies, paddle-like limbs, and long flattened tails, along with a unique pattern of armor along their backs made up of overlapping layers of bony osteoderms.

Hupehsuchus nanchangensis was a mid-sized member of the group, about 1m long (3’3″). Newly-discovered fossils of its skull show that its long flattened snout had a distinctive gap between the bones (similar to the platypus-like snout seen in its relative Eretmorhipis) with an overall shape surprisingly convergent with that of modern baleen whales – suggesting that this hupehsuchian may have been a similar sort of filter-feeder.

A diagram comparing Hupehsuchus' skull to that of a modern baleen whale. — *Hupehsuchus skull compared to a modern minke whale*
From fig 2 & fig 3 of Fang et al (2023). First filter feeding in the Early Triassic: cranial morphological convergence between *Hupehsuchus* and baleen whales. *BMC Ecol Evo* 23, 36. https://doi.org/10.1186/s12862-023-02143-9

Grooves in the bones along the outer edges of its upper jaws may be evidence of filtering structures similar to baleen, although with no soft-tissue preservation we don’t know exactly what this would have looked like. Its slender flexible lower jaws probably also supported a large expandable throat pouch, allowing it to filter plankton out of larger volumes of water.

Rechnisaurus

Rechnisaurus cristarhynchus here was a member of the dicynodonts, a group of stocky herbivorous beaky-jawed synapsids that were distantly related to modern mammals. Living in what is now eastern India during the Middle Triassic, about 247-242 million years ago, it’s only known from a single fossil skull – but based on the body proportions of better-known close relatives like Kannemeyeria it was probably somewhere around 1.2m long (~4′).

It had a raised bony crest running down the middle of its snout, with deep bowl-like depressions on either side that probably served to make the crest seem visually larger it already was. (They probably didn’t house any weird soft-tissue structures, however, since these type of dicynodonts tended to have very extensive keratinous coverings over their snouts.)

It also had raised bony areas around its parietal eye, and extensive bony flanges covering most of its tusks giving its face a sort of jowly appearance. All these features were probably for visual display and may have been brightly colored in life.

And, while I usually like to reconstruct dicynodonts as extensively fluffy… recently some fossil specimens of Lystrosaurus have been found showing bumpy leathery skin impressions. This doesn’t necessarily mean that all dicynodonts were hairless (especially since there are still those Permian coprolites), but since kannemeyeriiformes like Rechnisaurus were quite closely related to Lystrosaurus, I’ve gone with no fuzz at all on this one.

Tropidosuchus

Proterochampsids were a group of Triassic archosauriformes, closely related to the true archosaurs (crocodilians, pterosaurs, and dinosaurs/birds).

Known only from South America between about 242 and 205 million years ago, these reptiles’ heads were wide at the back but very narrow along the snout, often with prominent bony bumps and ridges on their skulls, and they had less osteoderm armor on their bodies than other archosauriformes.

They’ve traditionally been interpreted as very crocodile-like and semi-aquatic, but their long slender limbs and presence in rather arid paleoenvironments suggest they may have been more terrestrial fast-running predators.

Tropidosuchus romeri here lived about 235 million years ago in what is now Argentina. It was one of the smaller proterochampsids, only about 50cm long (1’8″), with just a single row of osteoderms along its back, and had larger and lower-set eyes compared to its relatives.

CT scans of its braincase indicate it had a particularly good sense of smell, and it may have relied mainly on scent to locate prey.

Spinosuchus

Allokotosaurs were a group of mostly-herbivorous archosauromorph reptiles, distantly related to the ancestors of crocodiles, pterosaurs, and dinosaurs. They lived across Eurasia, Africa, and North America during the mid-to-late Triassic period, and their lineage included some weird and diverse forms – such as the bull-horned Shringasaurus, the long-beaked Teraterpeton, and possibly also the gliding kuehneosaurids.

Spinosuchus caseanus here was yet another one of these Triassic allokotosaurian weirdos, part of the trilophosaurid family and closely related to Trilophosaurus and Teraterpeton.

Living about 221-212 million years ago in what is now northwest Texas, USA, Spinosuchus was around 2.2m long (~7’2″) and had distinctive elongated neural spines along the vertebrae of its back and the base of its tail, forming a “high back” or short “sail”. Since it’s only known from a partial spinal column the rest of its anatomy isn’t known for certain, but it probably had body proportions similar to its close relative Trilophosaurus, with sprawling limbs and a short-snouted beaked head adapted for herbivory.

Like many other fossil “sailbacked” animals the exact function of Spinosuchus’ elongated vertebrae is unclear, but the structure may have been used for visual display. I’ve depicted it here with a speculative frill of colorful elongated scales, along with a flashy dewlap.

Silesaurus

Silesaurus opolensis here was a type of dinosauriform – a reptile very closely related to the ancestors of true dinosaurs, but not quite actually a dinosaur itself.

Living in Poland during the Late Triassic (~230 million years ago), it was a quadrupedal animal roughly the size of a large modern dog, about 50cm tall at the shoulder (1’8″) and 2m long (6’6″). The front of its lower jaw was toothless and covered with a keratinous beak, and there may have been a corresponding much smaller beak at the very tip of its upper jaw, too.

It was originally thought to be a herbivore, but coprolites full of insect remains suggest it was probably more of an omnivore, possibly foraging by pecking in a convergently similar manner to its distant bird cousins.

In fact, one of those pieces of Silesaurus poop was recently found to preserve a new species of tiny beetle in incredible detail.

Eons Roundup 11

It’s time for another batch of PBS Eons commission work!

An illustration of an extinct marine reptile. It has a lizard-like body and a long paddle-like tail, and a small head with an oddly-shaped wide mouth lined with many tiny teeth – the overall shape of its bizarre jaws resembles the head of a vacuum cleaner! — Atopodentatus unicus

An illustration of an extinct marine reptile. It resembles a turtle with a wide squared-off beak, small spikes on the back of its head, and a wide carapace shaped vaguely like a horseshoe crab. — Atopodentatus unicus

The marine reptiles Atopodentatus and Henodus, from “The Triassic Reptile With ‘Two Faces'”
https://www.youtube.com/watch?v=-8W26SiCylI

An illustration of an extinct giant marine turtle. it has a ridged shell like a leatherback, and a hooked eagle-like beak. — Archelon ischyros

An illustration of an extinct sea turtle. — Archelon ischyros

The marine turtles Archelon and Euclastes, from “The Return of Giant Skin-Shell Sea Turtles”
https://www.youtube.com/watch?v=Tmb8XCwb3FI