reptile – Page 4 – Nix Illustration

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”.

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.

Eons Roundup 4

Some more recent commission work for PBS Eons!

An illustration of an extinct entelodont, an omnivorous hoofed mammal. It has a hippo-like head and a body proportioned rather like a hyena, with high shoulders and long slender legs. It has cloven-hoofed feet and a short tail, and its body is covered in a coat of short bristly fur. — Eoentelodon

The entelodonts Eoentelodon and Brachyhyops, from “The Hellacious Lives of the Hell Pigs”
https://www.youtube.com/watch?v=trJpxwMGoCw

An illustration of an extinct ichthyosaur, an ancient marine reptile. It has a short narrow snout full of rounded teeth, large eyes, a long tapering body, four flippers, and a long tail ending in a vertical fin. — Tholodus

An illustration of an extinct mosasaur, an ancient marine reptile. It has long triangular jaws full of many small sharp teeth, a long lizard-like body, four paddle-like flippers, and a long tail ending in a vertical fin. — Tholodus

The early ichthyosaur Tholodus and the mosasaur Pluridens, from “When Ichthyosaurs Led a Revolution in the Seas”
https://www.youtube.com/watch?v=V342aXQs9XY

An illustration of an extinct early bat in flight. It has claws on all five fingers on each wing, along with small ears and a long tail. — Onychonycteris

An illustration of an extinct early bat in flight. It has claws on both its thumb and the first wing finger one each wing, along with small ears and a long tail. — Onychonycteris

The early bats Onychonycteris and Icaronycteris, from “When Bats Took Flight”
https://www.youtube.com/watch?v=zWeYCULC0UQ

Island Weirdness #26 – The Mauritian Giant Skink

Along with its unique birds, Mauritius was also home to many endemic reptile species. In the absence of terrestrial mammals giant tortoises were the largest herbivores on the island, and various geckos, skinks, and snakes helped to fill out the rest of the vertebrate ecosystem.

Leiolopisma mauritiana was a very large skink, one of the biggest ever known to have existed with a total length of around 80cm (2′7″). Its ancestors originated in Australasia, over 5600km away (~3500 miles) at least 3-4 million years ago – and they must have endured a particularly long ocean rafting journey without any island hopping stops, since none of the other islands along that route seem to have ever had populations of similar skinks.

It probably lived in rocky areas, possibly also being capable of digging burrows, and would have eaten an omnivorous diet of seeds, fruits, invertebrates, and smaller lizards and birds.

By the early 1600s it was already extinct, very soon after the arrival of humans, probably due to predation from invasive mammals like rats. However, its half-sized close relative Leiolopisma telfairii does still survive on rat-free Round Island a short distance to the north of Mauritius, and recent conservation efforts have been rebuilding its population and setting up new colonies on other nearby small islands.

Almost-Living Fossils Month #23 – Enamel-Armored Lizards

The glyptosaurines were a group of lizards that first appeared in the Late Cretaceous, about 85 million years ago. They were an early branch of the anguid lineage, originating in North America, and had heavily armored bodies covered in bony osteoderms – superficially similar to those of modern beaded lizards, but structurally much more complex with the outermost layer formed from a unique enamel-like substance called osteodermine.

They were some of the few lizards to survived through the end-Cretaceous extinction 66 million years ago (which killed off over 80% of the lizard species known at the time) and went on to become quite successful in the warm climates of the early Cenozoic.

They spread across to Europe and Asia and developed much larger body sizes, going from small 10cm-long (4″) forms in the Early Paleocene (~65 mya) to over 60cm long (2′) by the mid-Eocene (~40 mya). In North America and Europe they became common enough that they were probably important parts of the local ecosystems, and their widespread distribution suggests they were able to adapt to a variety of different habitats and environmental niches.

Their teeth resembled those of modern omnivorous lizards like blue-tongued skinks, suggesting they had a similar generalist diet – although their strong jaws have also been proposed to be specializations for crushing hard-shelled invertebrates such as snails.

Helodermoides tuberculatus here was one of the largest glyptosaurines, about 65cm long (2′2″). It lived during the Late Eocene and Early Oligocene (~34-33 mya) in the northwestern and midwestern United States, with fossils known from Montana, Wyoming, and Nebraska.

One fossil shows evidence of having lost part of its tail, probably dropping it in a self-defense behavior to escape a predator. However, unlike the regenerating tails of many other lizards, the osteoderms of Helodermoides instead seem to have formed a thick rounded bony cap over the wound, preventing any significant regrowth and leaving its tail permanently stumpy.

During the Late Eocene and Early Oligocene the glyptosaurines began to disappear, probably struggling to cope with cooling and drying climates, and their last definite fossils date to about 30 million years ago. Possible fragmentary remains from as late as the Early Miocene of Central Europe (~16 mya) may indicate that a few isolated late-surviving members of the group persisted on for a while longer, but if they did hang on that long they were probably finished off by further sharp temperature drops in the mid-Miocene.

Almost-Living Fossils Month #20 – Some Very Spiky Turtles

The meiolaniformes were a group of terrestrial turtles that first appeared in the fossil record in the Early Cretaceous, around 125 million years ago. Although they were originally thought to be cryptodirans, more recent studies suggest they weren’t actually quite true turtles at all, instead being close evolutionary cousins to them in a much older and more “primitive” lineage that may go back as far as the Triassic.

They’re known mainly from South America and Oceania, but they may have had a more global distribution during the Cretaceous, with some fossils from the northern continents sometimes being classified as members of the group. However, only the South American meiolaniformes seem to have actually survived through the end-Cretaceous extinction.

The most distinctive meiolaniformes were the heavily armored meiolaniids, which first appeared in Patagonia during the Early Eocene (~48 mya). With large horns on their heads and thorn-like spikes along their long tails, they seem to have convergently evolved to fill the same sort of large-herbivore-tank niche as ankylosaurs and glyptodonts.

They also had fairly large nasal cavities, which might indicate a well-developed sense of smell – or may have been an adaptation for regulating the heat and moisture content of each breath, similar to the complex noses of ankylosaurs.

The South American meiolaniformes all went extinct around the end of the Eocene (~33 mya), but some meiolaniids had already dispersed across to Australia via Antarctica (before the continents had fully separated, and before Antarctica had frozen over) and they continued to survive there for most of the rest of the Cenozoic. They even went on to spread to various islands around Oceania, suggesting they were able to float and swim like modern giant tortoises.

The largest Australian meiolaniids reached sizes of around 2.5m long (8′2″), making them some of the biggest of all known terrestrial turtles. These giant forms went extinct in the Late Pleistocene, around 50,000 years ago, alongside much of the other Australian megafauna.

A few smaller varieties hung on in smaller islands to the east, with one of the latest-surviving species being Meiolania platyceps on Lord Howe island. It was only about half the size of its biggest Australian relatives – an example of insular dwarfism – and lived into the Late Holocene just 3000-2000 years ago.

Meiolania species on other islands seem to have gone extinct after the arrival of humans. But Lord Howe Island appears to have never been inhabited prior to European settlement in the late 1700s, so it’s unclear why this last of the meiolaniformes disappeared.

[Edit: A 2018 study of Meiolania platyceps’ anatomy suggests it may have been more aquatic than previously thought. It might have been something like a giant herbivorous snapping turtle or an armored reptilian hippo, bottom-walking around in coastal lagoons, with its big nasal cavity housing salt glands.]

Almost-Living Fossils Month #14 – Ancient Snakes

While the evolutionary origin of snakes is still rather poorly understood, one very early branch of their lineage – known as the madtsoiids – were a particularly long-lived group.

Originating back in the mid-Cretaceous (~100 mya), these “primitive” snakes were found mostly in the southern continents of Gondwana (known from South America, Africa, India, and Australia), but a few also spread into Europe. They were either some of the earliest true snakes or perhaps ophidians very closely related to them, and may have retained small hindlimbs that were slightly more well-developed than the vestigal ones of some modern snakes.

They ranged in length from under 1m (3′3″) to at least 7m (23′), with biggest of them rivaling some of the very largest living snakes in size.

They would have been similar to pythons, non-venomous and relying on constriction to kill their prey, although they had less flexible skulls than their modern relatives and couldn’t easily swallow animals much larger than their own heads. At least some of the Cretaceous species would have preyed on smaller dinosaurs, with one fossil even preserving a mid-sized madtsoiid in a sauropod nest alongside a hatchling.

Although the madtsoiids survived the end-Cretaceous extinction quite well and kept going throughout most of their range for the first half of the Cenozoic, most of them eventually disappeared in the Eocene-Oligocene extinction about 33 million years ago.

Aside from a single possible Late Olgiocene/Early Miocene record from South America (~29-21 mya), after that point the madtsoiids were found only in Australia, where they persisted almost into modern times.

Wonambi naracoortensis was one of the last of the Australian madtsoiids, living from the mid-Miocene (~11 mya) to at least the Late Pleistocene (~40,000 years ago). It was also one of the larger members of the group, 5-6m long (16′5″-19′8″), and seems to have been an ambush predator that lurked around waterholes to catch drinking animals.

The last madtsoiids went extinct at the same time as many of the other Australian megafauna, and it’s not clear exactly what caused them to die out. Humans had arrived in Australia about 20,000 years earlier, and hunting – either directly targeting the large snakes, or simply gradually reducing their available prey – combined with a changing climate may have been too much for them to handle.

Almost-Living Fossils Month #05 – Cryptic Choristoderes

The choristoderes were a group of aquatic reptiles that mostly inhabited freshwater environments. Known mainly from North America, Europe, and Asia, they first appeared in the fossil record in the Late Triassic (~205 mya) – although their lineage could potentially go back further than that – and they varied in appearance from large long-snouted croc-like creatures to more lizard-like and miniature plesiosaur-like forms.

Many them were fully aquatic and spent their entire lives in the water, with some developing the ability to give live birth and others returning to land only to lay eggs (with only females having well-developed enough limbs to be able to haul themselves out onto shore). In some places their fossils are incredibly common, with every life stage represented from babies to adults (even one with two heads!), and yet despite having such detailed knowledge of their lives we still don’t know exactly what type of reptile they actually were.

Their evolutionary origins and relationships are very unclear, with the only real certainly being that they’re at least diapsids. They’re often classified as either archosauromorphs (closer related to crocodilians and dinosaurs/birds) or as lepidosauromorphs (closer related to lizards), but they could also be a much earlier separate branch of the reptile family tree.

Some of the large crocodilian-like neochoristoderes survived into the Cenozoic and initially did quite well for themselves – even outcompeting actual crocodilians in the northern continents for a while – but then they seem to have fallen victim to the cooling and drying climate of the Eocene-Oligocene extinction about 33 million years ago.

But that wasn’t the end of the choristodere lineage just yet.

A small number of fossils of a little choristodere named Lazarussuchus have been found in a few different places around Europe, with the youngest specimens dating to as recently as the Early Miocene (~20-16 mya). Surprisingly it wasn’t closely related to the neochoristoderes at all, but instead seems to have been part of a much older and more “primitive” branch of the choristodere family tree that must have been surviving since at least the mid-Jurassic with very little presence in the fossil record.

At about 30cm long (1′) it was less aquatic than most other choristoderes, with large claws that would have given it good traction on land and a more generalized lizard-like body plan. One specimen even preserves soft tissue impressions, showing that its toes lacked webbing and that it had a low crest running along its tail.

Its lack of specialization may have been the reason for its longer survival, being able to adapt to a wider variety of environments compared to its more water-reliant cousins.

It’s unclear exactly how much closer to present day these rare last choristoderes survived. If they managed to make it through the mid-Miocene extinction then they might potentially have persisted until the onset of the Pleistocene Ice Age 2.5 million years ago – but their fossils are scarce enough that we’ll probably never know for certain.

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.