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.
The modern tuatara is the only living representative of an entire major lineage of reptiles known as sphenodontians – an evolutionary “cousin” group to all lizards and snakes, last sharing a common ancestor with them over 240 million years ago.
And during the Triassic and Jurassic these lizard-like animals were a widespread and diverse bunch, found worldwide and occupying many of the ecological roles that were later taken over by true lizards. They ranged from tiny insectivores to omnivores, relatively large herbivores, and specialized shell-crushers – and some even adapted to a fully aquatic fish-eating lifestyle.
Pleurosaurus ginsburgi here lived during the Late Jurassic, about 150-145 million years ago, in the warm shallow seas and lagoons that covered most of Europe at that time. Fossils of this particular species are known from southern France, with the closely related Pleurosaurus goldfussi found in both the same region and the German Solnhofen Limestone.
These swimming sphenodontians could grow to around 1.5 in length (~5′), with elongated bodies, pointed triangular snouts with retracted nostrils, short flipper-like forelimbs, and especially long eel-like tails. Soft tissue impressions also show scaly skin covering their bodies and a “frill” running along the top of the tail.
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.
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.
During the late Cretaceous period, about 72-66 million years ago, the Oulad Abdoun Basin region of Morocco was submerged under the Atlantic ocean – and the water above it was absolutely teeming with mosasaurs.
Fossils of at least a dozen different species of these predatory marine reptiles have been found in the area, and they seem to have all been occupying different ecological roles to avoid being in direct competition with each other. Many had conical piercing teeth adapted for gripping onto slippery soft-bodied prey, but others had rounded blunt teeth for crushing hard shells, and some even had sharp shark-like teeth for tearing flesh.
And one of the most surprising recent discoveries from this diverse ecosystem was Gavialimimus almaghribensis.
This 7m long (23′) mosasaur was part of the plioplatecarpine lineage, but it had uniquely long and narrow jaws with pointy interlocking teeth and highly retracted nostrils. Its snout shape resembled that of a crocodilians like modern gharials more than any of its short-skulled close relatives, and it was probably specialized for a similar diet of small fast-moving fish.
Mainly known from mid-Triassic deposits on the Swiss-Italian border, dating around 247–235 million years ago, fossils of the species Tanystropheus longobardicus have been found in two different “morphs” – small forms less than 2m long (6’6″), and larger ones up to 6m long (19’8″).
For a long time the smaller fossils were thought to be juveniles, but while they certainly had juvenile-looking facial proportions they also had very different teeth compared to the larger forms. They had pointed teeth at the front of their mouths and multi-cusped cheek teeth further back, and the “adults” had jaws containing only the pointed teeth, suggesting very different diets and lifestyles between the two size classes.
Extreme changes in dentition and diet during maturation aren’t unheard of in fossil species, but something particularly odd was going on here. Larger forms over 2m long always had just the pointed teeth, and there were no signs of intermediate tooth arrangements at all.
And a new study using x-ray microtomography has given an answer: they weren’t actually the same species!
Turns out the smaller Tanystropheus longobardicus were all skeletally mature adults, already fully grown at that size. The larger ones were a completely separate species occupying a different ecological niche to their smaller relatives, and have been named Tanystropheus hydroides in reference to the mythical hydra.
Comparison of the skulls of T. hydroides and T. longobardicus
[ From fig 3 in Spiekman, S. N. et al (2020). Aquatic Habits and Niche Partitioning in the Extraordinarily Long-Necked Triassic Reptile Tanystropheus. Current Biology. https://doi.org/10.1016/j.cub.2020.07.025 ]
While the exact lifestyle of Tanystropheus is an ongoing paleontological argument, Tanystropheus hydroides at least appears to have been much more on the aquatic side of things, with nostrils positioned on the top of its snout and its pointed teeth forming a “fish trap” in its jaws.
Stomach contents suggest it mainly ate fast-moving aquatic prey like fish and cephalopods, but its body wasn’t really adapted for strong swimming and so it couldn’t have been catching them via active pursuit. Instead it was probably an ambush predator hunting in a similar manner to some plesiosaurs, using its incredibly long neck and relatively small head to carefully approach prey species without the rest of its body startling them, and then catching them with fast snapping sideways lunges.
Mixosaurus cornalianus here was a small early ichthyosaur, only about 0.8-1m long (2’7″-3’3″) and generally considered to be transitional between the eel-like swimming style of basal forms and the more dolphin-like later forms. Living during the Middle Triassic, about 242 million years ago, it inhabited a shallow tropical sea that covered what is now the modern border between Switzerland and Italy.
It was previously thought to be a slow swimmer with a low and poorly-developed tail fin, and whether it even had a dorsal fin or not was unclear. But now new specimens with soft tissue impressions have given us a big surprise.
Not only did it actually have a fairly well-developed semilunate tail fin, but it also had a dorsal fin positioned much further forward on its body than expected, giving it a shape similar to some small sharks and representing the current earliest known dorsal fin of any amniote.
Bundles of stiffening collagen fibers inside its fins were very similar to those known from later Jurassic ichthyosaur species, indicating that this adaptation evolved much earlier in the lineage than previously thought. Along with stomach contents showing it mainly ate both cephalopods and small fish – fairly fast-moving prey – this suggests it was a capable open-water swimmer. It wouldn’t have been quite as speedy as its much more specialized Jurassic relatives, but it may have still been about as efficient as the small modern sharks it resembled.
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.
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.
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.
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.
