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.

Hovasaurus

The Permian-Triassic extinction 252 million years ago was the most severe mass extinction in Earth’s history, so incredibly devastating that it’s been nicknamed the “Great Dying” – but there were still some animals that somehow just… didn’t seem to really notice it at all.

And one of these surprisingly resilient species was Hovasaurus boulei.

It was part of a group known as the tangasaurids, a fairly early evolutionary branch of diapsid reptiles from Madagascar and East Africa that originated sometime in the mid-Permian, just before the common ancestor of modern lizards and archosaurs.

Hovasaurus lived in Madagascar both just before and for some time after the Great Dying, dating to around 252-247 million years ago. Growing up to about 90cm long (~3′), it was one of the largest tangasaurids and was also highly specialized for aquatic life in freshwater rivers, with an eel-like tail twice the length of the rest of its body and heavy thickened ribs.

Hundreds of fossils have been found representing life stages from hatchling to adult, and juvenile Hovasaurus actually seem to have been almost fully aquatic – they had proportionally shorter limbs and may have behaved similarly to modern sea turtles, crawling into the water shortly after hatching and only returning to land as adults once they had longer better-developed legs.

Many fossils also preserve clusters of pebbles in their abdominal cavities, which are thought to have been used as extra ballast to help weigh them down in the water when hunting small fish and invertebrates.

It’s not entirely clear why these odd little aquatic reptiles were apparently unaffected by the Great Dying. Perhaps, much like the many freshwater species that survived though the later end-Cretaceous mass extinction, Hovasaurus was simply very good at dealing with sudden changes in its environment and food availability due to the variability of river habitats, and was able to weather though the worst of the extinction without much trouble. 

Or maybe it was just one of the lucky ones.

Xinpusaurus

Thalattosaurs were a weird and rather mysterious group of Triassic marine reptiles. It’s not clear where they actually fit on the reptile evolutionary tree (we know they’re diapsids, but nobody can really agree on anything more definite than that), and they had some very strange skulls that seem to have been highly specialized for something, although their actual function is still unknown.

Xinpusaurus kohi here is known from the Late Triassic of China (~232-221 mya). About 1.3m long (4′3″), with half of that being its paddle-like tail, it had an elongated upper jaw that formed a protruding pointed spear-shaped snout.

It’s not clear whether this odd snoot was an adaptation for hunting similar to the long bills of swordfish – there’s quite a bit of variation in length and shape between different individual specimens – or if it was serving some other purpose like the sexually dimorphic noses of some modern lizards.