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!

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


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

Stenaulorhynchus

Taking place during the 50-million year span between two huge mass extinctions, the Triassic was a very weird time. At the start of the period there was world domination by the synapsid Lystrosaurus, then after a few million years of recovery time came an evolutionary “explosion” from the rest of the survivors – filling new roles in their ecosystems and producing a brief but bizarre menagerie of unique species.

And one of the groups that rose to prominence during this time were the rhynchosaurs. Part of the archosauromorph branch of reptiles, they were closely related to the ancestors of crocodilians, pterosaurs, and dinosaurs, and evolved from small superficially lizard-like forms living in southern Africa during the very start of the Triassic, around 250 million years ago. But within just a few million years they became larger and bulkier, specialized for herbivory and scratch digging, and they soon spread all over Pangaea and became incredibly abundant in some fossil deposits.

Stenaulorhynchus stockleyi was one of larger member of this lineage, around 1.2m long (4’), known from Tanzania about 247-242 million years ago. It had a typical triangular rhynchosaurian skull, with wide deep cheeks supporting powerful jaw muscles and multiple rows of grinding teeth, along with a narrow hooked “beak” formed from the premaxillary bones of its snout.

Its unclear what the actual life appearance of the rhynchosaur “beak” was, with some reconstructions having a shrinkwrapped “alien mole-rat” look, others giving them keratinous parrot-like actual beaks, and still others going with fleshy tuatara-like lizard lips. In the past I’ve leaned somewhat towards the latter, but since one fossil does actually show some evidence for a keratinous covering I’ve gone for an extensive full beak this time around.

Ancistronychus

Drepanosaurs were already some extremely weird animals, even among all the other weirdos of the Triassic period.

These strange little tree-climbing reptiles had chameleon-like bodies, humped backs, long necks, and oddly bird-like skulls with toothless beaks – and then some of them also had bizarre forelimb anatomy with a single enormous claw on the second finger of each hand, along with a claw on the tip of their prehensile tail.

But new discoveries are showing that some members of this bizarre group were doing something different.

Ancistronychus paradoxus here lived during the late Triassic, about 227 million years ago, in what is now the southwestern United States. Measuring around 50cm long (1’8″), its enormous hand claws were unusual compared to its close relatives, with a distinctly wide and hooked shovel-like shape.

Along with another recently-discovered species, Skybalonyx skapter, and the weird burly arms of Drepanosaurus, this suggests that instead of tree-climbing some drepanosaurs were instead much more specialized for digging. They may have been Triassic equivalents to modern anteaters or pangolins, using their enlarged claws to excavate burrows and rip their way into insect nests.

Weird Heads Month #24: Hook-Snouted Swimmers

Thalattosaurs were another group of weird Triassic animals, found in coastal marine environments all around the world. Their evolutionary relationships are unclear beyond “they were some sort of diapsid reptile”, and they were well adapted for aquatic life, with streamlined lizard-like bodies, short limbs with webbed feet, and long paddle-like tails.

Most of them had long narrow toothy snouts, but others had odd spear-shaped noses or downturned upper jaws

Hescheleria rubeli here was one of the strangest, living in Europe during the mid Triassic, about 247-235 million years ago. It was one of the smaller known species of thalattosaurs, around 1m long (3’3″), and had a particularly bizarre-looking head.

A close-up of the head of the extinct marine reptile Hescheleria. The front of its snout is sharply downturned, forming a near-right-angled hooked shape, with small sharp teeth at the front of its jaws along with a pair of large conical bony projections in its lower jaw.

Its snout was so sharply curved downward that it formed a right-angled hook relative to the rest of its jaws, sort of resembling the initial interpretation of Atopodentatus but without the vertical split.

There were also small sharp teeth at the front of its mouth, along with a pair of large conical bony projections on its lower jaw.

This weird arrangement must have been highly specialized for something, but its actual function is still unknown. One suggestion is that the large jaw-spikes were used to crunch into hard-shelled prey, although there doesn’t seem to have been any reinforced surface in the upper jaw for them to crush against.

But I personally wonder if maybe these jaws were the equivalent of the hooked kypes seen in the males of some modern salmonid fish – structures associated with dominance fighting.

Weird Heads Month #15: Hammerhead Reptiles

Atopodentatus unicus lived in Southwest China during the early-to-mid Triassic, around 247-240 million years ago. About 3m long (9’10”), it was a marine reptile – probably part of an early branch of the sauropterygians – with an elongated streamlined body and paddle-like limbs.

When it was originally described in 2014 it seemed to have a head unlike anything seen before. The skull of the only known fossil specimen was incomplete and badly crushed, but it was reconstructed as having a downward-hooking upper jaw with a vertical split in the middle forming a zipper-like row of teeth.

An illustration of the old interpretation of Atopodentatus. It has a bizarre vertical split in the front of its snout full of needle-like teeth resembling a zipper.
The original version of Atopodentatus

But then just two years later some more complete skulls were discovered and revealed something completely different: the projections on Atopodentatus‘ snout actually stuck out to each side in a wide flat “hammerhead” shape on both its upper and lower jaws.

Not quite as bizarre as before, but still a Triassic weirdo!

It also seems to have been a rare example of a herbivorous Mesozoic marine reptile, probably rooting around on the seafloor with its shovel-like mouth, using its chisel-shaped front teeth to scoop up mouthfuls of algae and other marine plants and then straining out the water through its closely spaced needle-like back teeth.

Weird Heads Month #07: The Wonderful Creeping Thing

The Triassic was an incredibly weird time, full of evolutionary experiments in the wake of the worst mass extinction in Earth’s history.

Teraterpeton hrynewichorum here was part of group known as allokotosaurs, a lineage of mostly-herbivorous archosauromorphs that also included the long-necked bull-horned Shringasaurus.

Living in Nova Scotia during the Late Triassic, around 235-221 million years ago, Teraterpeton (meaning “wonderful creeping thing”) was first named in the early 2000s based on a skull and partial skeleton, with some additional skeletal material being described recently in 2019.

Its head had a confusing mix of anatomical features, with a long beak-like toothless snout at the front of its jaws, small sharp interlocking cheek teeth further back, a huge nasal opening, and a closed-up fenestra at the back of its skull making it look more like the skulls of marine reptiles.

It also had a lizard-like body, perhaps up to 1.8m long (~6′), with rather long slender limbs and large blade-like claws, and more anatomical weirdness in the pelvic region convergently resembling those of distantly related groups like rhynchosaurs and tanystropheids. It had a sprawling posture, but its hind limb musculature suggests it might have been capable of getting up into a more erect stance when walking, somewhat similar to modern crocodilians’ “high walk” gait.

It was clearly quite an ecologically specialized animal, but quite what it was specialized for is still uncertain. It was presumably a herbivore like its close relatives, but it must have been eating a very different diet with its long beak, and its deep claws could have been used for scratch digging to get at roots and tubers.

Another possibility it that it could have been an insectivore with a diet similar to modern aardvarks or armadillos, probing with its beak and digging with its claws for insects, grubs, and other invertebrates. Since termite-like social insect nests do seem to have existed around the same time, it might even have been one the earliest known animals to specialize in myrmecophagy.

Weird Heads Month #05: Crested Snorkelers

Phytosaurs were a lineage of incredibly crocodile-like archosauriformes – essentially “crocodiles before crocodiles” – convergently evolving an incredibly similar appearance at a time when the ancestors of modern crocs were still small and terrestrial.

But while they had toothy snouts and bodies heavily armored with bony ostederms, unlike crocodilians their nostrils were far back on their heads up near their eyes, often in a sort of bony “snorkel” so they could breathe while almost fully submerged underwater.

Mystriosuchus westphali lived in Germany during the Late Triassic, about 215-212 million years ago. Around 4m long (~13′), it was even more aquatic than other phytosaurs, with paddle-like limbs and long slender gharial-like jaws adapted for catching slippery prey.

And along with the typical phytosaur snorkel, it also had raised crests along its upper jaw – which may have supported even larger keratinous display structures.

Weird Heads Month #03: Big Head Mode

In the last entry we had heads that looked much too small… so now how about heads that were too big?

Erythrosuchus africanus was part of an early branch of the archosauriformes, related to the ancestors of crocodiles, pterosaurs, and dinosaurs. Living in South Africa during the mid Triassic, around 247-242 million years ago, it was the largest predator of its time, reaching about 5m long (16’5″).

It was one of the earliest archosaurifomes to develop a more upright-limbed posture, and convergently evolved a very theropod-like head with a deep narrow snout full of large serrated teeth.

A head that was absolutely massive proportional to the rest of its body, measuring about 1m long (3’3″).

As a result of such a big noggin, Erythrosuchus must have also had some bulky musculature in its neck and forequarters to support it. And while its fairly short neck wouldn’t have been very flexible buried in all that tissue, it probably didn’t need to be – some of its main prey would have been large slow-moving dicynodonts, and its hunting strategy may have consisted of simply “aim at food and lunge”.

Shonisaurus

Most ichthyosaurs were similar in size to the modern dolphins they convergently resembled, but during the Late Triassic some of them got much much bigger.

Shonisaurus popularis lived about 222-212 million years ago, in Nevada, USA — a region that’s currently made up of dry deserts, but which was submerged under a tropical inland sea at the time.

At around 15m long (49′) it was roughly the same size as a modern humpback whale, with a long narrow snout, a fairly deep fusiform body, and four equally-sized flippers. Unlike many other ichthyosaurs it doesn’t seem to have had a dorsal fin, and its tail fluke shape was rather “primitive” indicating it was probably a slow cruising swimmer.

Juveniles had a few small teeth at the tips of their jaws, but larger adults were entirely toothless, suggesting that they may have specialized in different ecological niches at different stages of their lives. Fully-grown Shonisaurus probably mostly fed on prey such as soft-bodied cephalopods and small fish, which must have been incredibly abundant in the ancient Nevadan sea to support a population of such huge marine reptiles.

But Shonisaurus popularis wasn’t even the biggest of the Late Triassic giant ichthyosaurs. Further north in British Columbia, the closely related species Shonisaurus sikanniensis reached lengths of up to 21m (69′), and fragmentary remains from England hint at something even larger still, estimated at around 25m (82′) – close in size to the modern blue whale, and potentially being the largest non-dinosaurian reptile to ever live.