Panzhousaurus

Panzhousaurus rotundirostris, a sauropterygian marine reptile from the mid-Triassic of southwestern China (~245 mya), living just a few million years after the devastating Permian-Triassic mass extinction. This small marine reptile was only about 40cm long (1′4″) and is known from a single near-complete skeleton.

Although it was a distant evolutionary cousin to plesiosaurs (and even more distantly to modern turtles), it was actually most closely related to an early sauropterygian lineage known as the pachypleurosaurs – a group of small lizard-like aquatic reptiles with tiny heads, long necks, and paddle-like limbs.

It had an unusually short and rounded-off snout compared to its relatives, and since it would have lived alongside many other diverse marine reptiles it was probably specialized for a slightly different ecological niche.

Anomalochelys

Anomalochelys angulata, a terrestrial turtle from the mid-Cretaceous of Hokkaido, Japan (~100-94 mya).

Measuring around 60cm long (2′), it had a pair of large forward-facing horn-like spikes at the front of its shell – the function of which isn’t clear, but they may have been useful for defense if it was incapable of fully retracting its head into its shell.

It was part of a family of turtles from Asia and North America known as nanhsiungchelyids, a group that adapted to live fully on land and ended up convergently closely resembling modern tortoises. Other members of this group included the larger Nanhsiungchelys (which was also recently found to have possessed “horns” on its shell!) and the very flat Basilemys.

They were also a rare example of a turtle family that didn’t survive through the end-Cretaceous mass extinction, with no known remains from the Cenozoic.

Ocepechelon

Ocepechelon bouyai, a sea turtle from the late Cretaceous of Morocco (~70-66 mya). Closely related to the modern leatherback turtle and the pug-nosed Alienochelys, it’s only known from a single 70cm-long skull (2′4″) – and while its body proportions aren’t known for certain it was probably very big, possibly up to 4m long (13′).

Unlike any other known turtle it had a unique narrow tube-shaped snout. This is thought to be an adaptation for suction feeding, vacuuming up tiny fish, squid, and jellyfish in a similar manner to modern pipefish or beaked whales.

Paludidraco

Paludidraco multidentatus from the Late Triassic of Spain (~237-227 mya).

This 3m long (9′10″) animal was a member of the nothosaurs, a group of semi-aquatic seal-like marine reptiles that were closely related to plesiosaurs (and both were also evolutionary cousins to modern turtles).

It had long slender jaws full of numerous tiny teeth, creating an interlocking comb that was probably used for filter feeding – scooping up mouthfuls of fine-grained sediment from the seafloor and filtering out small invertebrates or soft plant matter.

The bones of its skeleton were also highly thickened and dense, a condition known as pachyostosis that provided ballast to weigh it down in the water. This would have made it a slow and unmaneuverable swimmer, but a very energy-efficient one, using its natural neutral buoyancy to hover or walk along the seabed.

It was essentially a reptilian manatee, filling a similar sort of ecological niche.

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.]

Alienochelys

Alienochelys selloumi, a sea turtle from the Late Cretaceous of Morocco (70-66 mya). Although only known from a single skull, it was probably around 2-2.5m long (6′6″- 8′2″), and was closely related to both the modern leatherback turtle and the giant Archelon – and so it wouldn’t have had a solid shell but instead a leathery skin-covered carapace.

But that one skull was also incredibly weird. While most turtles have pointed beaks, Alienochelys had a blunt squared-off face, sort of “pug-nosed”, with its nostrils set high up between its eyes. It seems to have been specialized for crushing hard-shelled prey between the wide flat grinding surfaces of its beak, more similar to the jaws of rays than those of other turtles.

It also lived alongside another bizarre-jawed turtle, but that’s a subject for another time.

Gamerabaena

Gamerabaena sonsalla, a baenid freshwater turtle that lived at the very end of the Cretaceous (~66 mya) in North Dakota, USA. Known only from a single skull, its full size is uncertain, but it may have reached lengths of around 50cm (1′7″).

Its genus name was inspired by Gamera, a fictional giant turtle from a series of Japanese kaiju movies.

Baenids first appeared in the mid-Cretaceous (~112 mya) – although their ancestry may go as far back as the Late Jurassic (~150 mya) – and were part of an early lineage of the cryptodiran turtles, the grouping which includes most freshwater turtles and terrapins, all terrestrial tortoises, and all sea turtles. However, unlike many of the their modern cousins, they weren’t capable of fully retracting their heads inside their shells.

They survived well through the K-Pg mass extinction, with several species found on both sides of the boundary, but eventually went extinct in the mid-Eocene (~42 mya).

Mauriciosaurus

Mauriciosaurus fernandezi, a polycotylid plesiosaur from the Late Cretaceous of Mexico (~94-89 mya). About 1.9m long (6′3″) with a flipper-span of 1.5m (4′11″), it’s known from a near-complete skeleton with preserved soft tissue impressions. The fossil shows evidence of rows of very tiny scales, the skin outlines of the flippers, and also a thick layer of insulating blubbery fat.

Its body shape in life would have been similar to modern leatherback turtles, roughly teardrop-shaped and hydrodynamic – much chubbier than most plesiosaur reconstructions had been previously depicting!