#diapsid

Noriko Atrociraptor oc

By Tas Dixon

Etymology: Swiss Reptile 

First Described By: Peyer, 1955 

Classification: Biota, Archaea, Proteoarchaeota, Asgardarchaeota, Eukaryota, Neokaryota, Scotokaryota, Opimoda, Podiata, Amorphea, Obazoa, Opisthokonta, Holozoa, Filozoa, Choanozoa, Animalia, Eumetazoa, Parahoxozoa, Bilateria, Nephrozoa, Deuterostomia, Chordata, Olfactores, Vertebrata, Craniata, Gnathostomata, Eugnathostomata, Osteichthyes, Sarcopterygii, Rhipidistia, Tetrapodomorpha, Eotetrapodiformes, Elpistostegalia, Stegocephalia, Tetrapoda, Reptiliomorpha, Amniota, Sauropsida, Eureptilia, Romeriida, Diapsida, Neodiapsida, Sauria, Helveticosauridae 

Time and Place: Around 242 million years ago, on the Anisian-Ladinian boundary of the Middle Triassic

Helveticosaurus is known from the San Salvatore Formation of Italy and the Besano Formation of Switzerland

Physical Description: Helveticosaurus is one of the weirdest of Triassic marine oddities in terms of relationships - once thought to just be one of many different turtle relatives, it now seems to be a completely separate, just outside the group containing all living reptiles swimming creature utterly removed from the rest. It was a lopsided sort of creature, about 2 meters long with a widened torso - almost circular - short neck, and long tail. Its forelimbs were much longer than its hind limbs, and the tail was thickened at the top, sort of like the tail of a marine iguana, much like the contemporaneous Thalattosaurs. The head was small and rectangular, with sharp and pointed teeth filled throughout the mouth. It was probably covered in thick scales, and the hands and feet of Helveticosaurus were probably webbed to some degree. 

Diet: Given the sharp, pointy teeth, Helveticosaurus probably was a carnivore, eating a variety of fish, invertebrates, and probably its fellow marine reptiles. 

Behavior: Helveticosaurus had an extremely unique method of locomotion in the water. It was able to both undulate its body - sweeping it from side to side and using the tail to move through the water like living crocodilians and marine iguanas - and paddle, propelling itself forward with grand movements of its front limbs. These limbs were well built for swimming, and if Helveticosaurus hadn’t been an evolutionary dead end, it may have had one of the more unique methods of marine movement in the oceans. As a predator, it would have needed to use its weird swimming to reach for prey that one of the many other things it lived with could not get to. It also may have been able to come up onto the shore, perhaps feeding on animals nearby or going there to mate or escape danger in the ocean. That said, there are so many questions remaining about this oddball - did it lay its legs on land or give birth like most marine reptiles? Did it live on both the land and in the ocean for any length of time? In addition to this, the strange short face may or may not have allowed Helveticosaurus to be a suction feeder, sucking up the various small animals around it and snapping into them with its long teeth. This is just extra, and I’m giving up on trying to understand this thing now. Also, it couldn’t swim very well - at least, not like modern penguins or turtles - it didn’t fly, but made a good business out of doggy paddling and brute-forcing the action, making it one hardcore badass of a reptile. 

Ecosystem: Helveticosaurus lived near the Pangean coast, in the shallow marine waters of the Tethys sea. These marine habitats were probably open ocean, as little evidence of reef material is present in the same places as Helveticosaurus, though that is conjecture. Here it lived alongside a wide variety of brachiopods, as well as marine snails and Ammonites a plenty. There was also the Nothosaurs Nothosaurus and Lariosaurus; the Thalattosaurs Hescheleria, Clarazia, and Askeptosaurus; the Tanystropheids Tribelesodon Tanystropheus and Macrocnemus; the other Helveticosaurid Eusaurosphargis; the Placodonts Paraplacodus and Cyamodus; the Ichthyosaurs Cymbospondylus and Mixosaurus; the Pachypleurosaurs Serpianosaurus and Pachypleurosaurus; the Suchian Ticinosuchus; and an extremely wide variety of fish and sharks (to the point that it is literally impossible for me to list them all.) 

Other: We have no idea what Helveticosaurus is. We used to think it was a generic marine reptile, maybe a Placodont. Then, perhaps, an Archosauriform. Finally, now, we place it far apart from the rest, not even a proper Crown-Reptile. Still, the story isn’t over - maybe it, along with all other uniquely marine reptiles, are in one separate group? Who knows. These things are odd. I just can’t. It had two other relatives, one not named, the other Eosaurosphargis, which was even flatter around the middle. Honestly, it looks like a more plausible and marine Godzilla, in a weird, twisted way. Here we are. Triassic, what the fuck. 

~ By Meig Dickson 

Sources Under the Cut

By Scott Reid

Etymology: Sickle Reptile 

First Described By: Pinna 1979 

Classification: Biota, Archaea, Proteoarchaeota, Asgardarchaeota, Eukaryota, Neokaryota, Scotokaryota, Opimoda, Podiata, Amorphea, Obazoa, Opisthokonta, Holozoa, Filozoa, Choanozoa, Animalia, Eumetazoa, Parahoxozoa, Bilateria, Nephrozoa, Deuterostomia, Chordata, Olfactores, Vertebrata, Craniata, Gnathostomata, Eugnathostomata, Osteichthyes, Sarcopterygii, Rhipidistia, Tetrapodomorpha, Eotetrapodiformes, Elpistostegalia, Stegocephalia, Tetrapoda, Reptiliomorpha, Amniota, Sauropsida, Eureptilia, Romeriida, Diapsida, Neodiapsida, Sauria, Archosauromorpha, Protorosauria?, Drepanosauromorpha, Elyurosauria, Drepanosauridae, Megalancosaurinae 

Time and Place: 212 to 205 million years ago, from the Norian to the Rhaetian ages of the Late Triassic

Drepanosaurus is known from the Zorzino Limestone and Dolomia di Forni Formations of Italy, and the Siltstone and Petrified Forest Members of the Chinle Formation in New Mexico

Physical Description: Drepanosaurus is the Titular Member of the Drepanosaurs, aka the “Monkey Reptiles”! These weirdos got their name for a reason - they were extremely well adapted for climbing trees, to the point of having prehensile tails like many monkeys. Drepanosaurus had a long, slender body, with a very long and thick tail for grabbing onto branches and moving around the forest. It had a long, thin neck and a small skull on the end of it, which was superficially similar to the skull of a bird - it was round on the back end, with huge eyes and a small pointed snout. Still, that head looked more like the head of a chick any number of nonavian dinosaurs, rather than like birds. It had long, robust limbs, with claws on the digits. Most notably, one front claw on each Drepanosaurus hand was huge, used for aiding in gripping branches more easily. It had an arched shoulder region, and in general very high spines on its vertebrae. This made it look quite odd indeed - a lumpy, lengthy reptile that sort of looks like what would happen if you tried to combine a woodpecker, a monitor lizard, a monkey, and a bison into one small reptilian creature that lived in the trees of the Triassic. It was weird, okay. It was just weird. The tail may have even ended in a claw - that’s right, a claw - to help it grab onto branches better. And all of this weirdness was packed into a body only about 45 to 50 centimeters long - a truly specialized representative of Triassic Oddities. 

Diet: Drepanosaurus was most likely an insectivore, using the claws to help get out various insects from tree bark. 

Behavior: Drepanosaurus was a weirdo, but a weirdo with a purpose. All of these weird traits came together in one wild animal to aid it in climbing among trees, gathering food, and moving nimbly in the forest. The small, pointed mouth aided in digging out food from crevices and burrows, which it could open up bigger using the large claws. Its long and skinny neck also helped it to reach spots where insects were hiding, rather than wasting energy to move its entire body to where food was on the tree. The large, splayed out feet and strong claws were able to wrap around tree trunks, gripping the wood tightly and helping Drepanosaurus stay stabilized. The prehensile tail helped Drepanosaurus go from branch to branch and move among the tree canopy, and the claw would help to keep the tail in place during particularly slippery or dangerous swings. 

Ecosystem: Drepanosaurus lived in a variety of environments, most importantly the Triassic shores of Northern Italy, around tidal basins and seasonal lagoons. In the Zorzino beach formation, it shared its home with its close cousins, Megalancosaurus and Vallesaurus; as well as the early Pterosaurs Bergamodactylus, Peteinosaurus, and Eudimorphodon; the very long-snouted Phytosaur Mystriosuchus; the marine reptile Endennasaurus; the Placodont Psephoderma; the Aetosaur Aetosaurus; the Tuatara Diphydontosaurus; the Tanystropheid Langobardisaurus; and plenty of fish such as Legnonotus, Gibbodon, Sargodon, Pholidorhynchodon, Parapholidophorus, Pholidoctenus, Dapedium, Dandya, and the shark Pseudodalatias. This was a very active and diverse fauna, placing Drepanosaurus in one of the truly uniquely Triassic locations of the end of the Period. 

Dolomia di Forni was no sneeze either, a Tidal Basin surrounded by coniferous trees. Here we have some preservation of things that Drepanosaurus was likely to eat, such as the spider Friularachne. There were also plenty of crustaceans, including decapods and crab like things that would have been crawling all over the tidal pools. Fish were very common too, such as the Coelacanth Holophagus, the sharp fish man Saurichthys, other Ray-Finned fish such as Eopholidophorus and Sargodon, the shark Pseudoalatias, and the Conodont Epigondolella. There was also the Tanystropheid Langobardisaurus again, as well as the other Drepanosaur Megalancosaurus. However, the true heroes of the environment were the early pterosaurs - the whole gang was there, including Preondactylus, Eudimorphodon, Austriadactylus, and Seazzadactylus. It was just a huge chaos of flying reptiles, which Drepanosaurus would have had a tough time avoiding! 

Drepanosaurus has also been found in the Siltstone and Petrified Forest environments of the Chinle Formation in North America. Now, even in the context of Pangea this was a long distance away, but it’s possible they migrated there during the end of the Triassic period. These were thick coniferous forest environments with a severely dry and severely wet season, indicating that Drepanosaurus really adapted to a new cliimate, and quickly. Here there were famous animals such as the dinosaurs Coelophysis, Daemonosaurus, Chindesaurus, Tawa, the Silesaurid Eucoelophysis, the Lagerpetid Dromomeron, Pseudosuchians like Hesperosuchus, Effigia, Vivaron, and the Aetosaur Typothorax; the swimming Archosauromorph Vancleavea, Tuataras like Whitakersaurus, Phytosaurs like Redondasaurus and Rioarribasuchus, and even other Drepanosaurs like Avicranium (which might actually be what all the specimens of Drepanosaurus in the Chinle are, so take this with a grain of salt). This is a very diverse ecosystem that has been touched on elsewhere on WTF Triassic, so I will leave it at that! 

Other: Oh ye Drepanosaurs. With heads so birdlike and bodies so weird. Much like other triassic weirdos, BANDits (“scientists” who insist, though literally all evidence points to the contrary, that birds could not have evolved from dinosaurs), you have been fodder for speculation for ages. However, you have almost nothing in common with birds - even the skull is only similar on the outside, and lacks many of the features seen in bird skulls (that are, however, found in dinosaur skulls). In fact, many of these creatures were grouped together in a group called Avicephala, which was eventually abandoned as it was found that most of them were not closely related. That said, it was then found that Drepanosaurs were Archosauromorphs, showing that weird arboreal lifestyles were a trend in the Ruling Reptile group, rather than a unique feature of the birds. Though, it is possible that Drepanosaurs are actually very early Diapsids (reptiles proper), and thus may have evolved as early as the Permian - and somehow survived into the Triassic. More fossils are needed, but for now, they remain a fascinating and unique Triassic group, highlighting the weirdness of this timeperiod in a way few other animals can. 

~ By Meig Dickson

Sources Under the Cut

By Tas Dixon

Etymology: Named after Phillip Van Cleave

First Described By: Long & Murry, 1995

Classification: Biota, Archaea, Proteoarchaeota, Asgardarchaeota, Eukaryota, Neokaryota, Scotokaryota, Opimoda, Podiata, Amorphea, Obazoa, Opisthokonta, Holozoa, Filozoa, Choanozoa, Animalia, Eumetazoa, Parahoxozoa, Bilateria, Nephrozoa, Deuterostomia, Chordata, Olfactores, Vertebrata, Craniata, Gnathostomata, Eugnathostomata, Osteichthyes, Sarcopterygii, Rhipidistia, Tetrapodomorpha, Eotetrapodiformes, Elpistostegalia, Stegocephalia, Tetrapoda, Reptiliomorpha, Amniota, Sauropsida, Eureptilia, Romeriida, Diapsida, Neodiapsida, Sauria, Archosauromorpha, Crocopoda, Archosauriformes, Eucrocopoda, Proterochampsia?, Doswelliidae?

Status: Extinct 

Time and Place: 228 to 203.6 million years ago, in the Norian of the Late Triassic

Vancleavea is best known from the Petrified Forest in Arizona and Ghost Ranch in New Mexico, but is found throughout the Chinle Formation in Arizona, New Mexico, Texas and Utah in the southern United States. It is also known from the Tecovas Formation in Texas, and the Redonda and Bull Canyon Formations in New Mexico.

Physical Description: Vancleavea is a peculiar reptile, even by Triassic archosauromorph standards. It effectively resembles an armoured, scaly eel with tiny legs, a long neck, the tail of a crocodile and a frighteningly fang-toothed skull. The largest complete specimen is approximately 1.2 metres (3.9 feet) long, although isolated pieces from other specimens indicate it could grow larger. Most of its body is covered in an array of overlapping bony osteoderms that come in 5 different shapes on the main body, throat, underbelly, limbs and tail (as well as possibly some strange spike-like osteoderms of unknown position). Uniquely, the osteoderms on the tail are tall and flat from side to side, forming a tall fin along the top of the tail for swimming. No other tetrapod—except for the closely related Litorosuchus—has a tail fin like this (usually they are made of tall neural spines from the tail bones).

Vancleavea’s skull is also unusual, as it is very robust and solid, despite the relatively thin and pointed snout. The back of the skull is boxy and has completely closed over the upper temporal fenestra, leaving just the very large lower temporal fenestra. The antorbital fenestra in front of the eyes, a typical feature of archosauriform reptiles, has also been lost, and the snout is short with nostrils that point directly upwards. The jaw bones of Vancleavea are heavily pitted and have a rough texture, which combined with the large teeth imply Vancleavea lacked lips and had exposed fangs, similar to crocodiles. Vancleavea had three fangs on each side of its jaws, one at the front, one on the lower jaw, and another on the upper jaw behind the bottom fang. The dentary fang slotted into a gap in the upper jaw when the mouth was closed, again similar to crocodiles.

The body of Vancleavea is long and tubular, enhanced by both the unusually long neck and the small size of its limbs. It’s unlikely Vancleavea’s limbs were strong enough to lift its body off the ground on land, and in fact the forelimb is so reduced that the shape of some its finger bones suggests it had even lost the claws on its hands. All in all Vancleavea is very clearly built to be semi-, if not almost entirely, aquatic, swimming with a sinuous, eel-like motion and rarely crawling onto land, perhaps only to lay its eggs.

Diet: The massive, serrated fangs and conical teeth indicate Vancleavea was carnivorous, likely feeding on fish and other aquatic prey, such as small temnospondyl amphibians.

Behavior: Vancleavea is almost certainly semi-aquatic, using its deep, finned tail to scull through the water similar to living crocodilians. It’s speculated that Vancleavea lived as an ambush predator, lunging forward to snag prey in its fangs. It lived in slow-moving freshwater environments, and its elongated, sinuous body would have been perfect for winding through plants and logs and other obstacles in the water.

Ecosystem: Vancleavea is known from much of the Chinle Formation, one of the most well known Late Triassic formations in the world, and its longevity means that it coexisted with a wide variety of other animals. There were of course the dinosaurs, including the likes of Coelophysis, Chindesaurus and Daemonosaurus, along with other dinosauriforms such as silesaurids and the lagerpetid Dromomeron, as well as early pterosaurs. Pseudosuchian archosaurs were incredibly abundant, such as the numerous herbivorous aetosaurs and Revueltosaurus, the dinosaur-like poposauroids including the herbivorous beaked Shuvosaurus and Effigia, as well as the predatory Poposaurus. Rauisuchid pseudosuchians were among the top predators, such as Postosuchus, while small long-legged crocodylomorphs like Hesperosuchus and Parrishia chased after smaller prey. Various other archosauromorphs were present too, including the bizarre drepanosaurs, herbivorous allokotosaurs such as Trilophosaurus and an unnamed azendohsaurid, and the strange armoured Doswellia, possibly Vancleavea’s closest relative. There was even an early turtle, Chinlechelys, one of the earliest known to have a fully formed shell, and a relative of the tuatara, Whitakersaurus. The only definitively known synapsid from the Chinle is the large herbivorous dicynodont Placerias.

In the water, Vancleavea would have coexisted with numerous species of giant phytosaurs—crocodile-like reptiles that may-or-may-not be pseudosuchians—such as Leptosuchus and Machaeoprosopus, as well as the predatory temnospondyl amphibian Anaschisma (formerly known as Koskinonodon). Vancleavea’s heavy armour may have been necessary protection against these predators, which could have had jaws almost as long as it was! Fish were abundant in the freshwater ecosystem, with various ray-finned fish such as the pike-like Saurichthys, the large lungfish Arganodus, freshwater sharks such as Xenacanthus, and even a freshwater coelacanth, Chinlea. Many of these fish grew to as large or larger than Vancleavea, and may have competed with it or even preyed upon it (at least as juveniles).

Vancleavea also coexisted with several other, more mysterious reptiles that are mostly only known from teeth. One of these, Acallosuchus, was discovered close by to the original specimen of Vancleavea. The skull and skeleton were originally suggested to belong to the same animal, but we now know Vancleavea had a very different skull to Acallosuchus. Supposedly its skull was long, pointed and triangular, with a knobbly texture on the bones. I say “supposedly” because the skull disintegrated while it was excavated, and all that’s left is a crude drawing and a few pieces of bone. The identity of Acallosuchus remains a mystery. Other mysterious species that Vancleavea coexisted with are the former ornithischians Tecovasaurus and Crosbysaurus, Colognathus, Palacrodon, the possibly venomous Uatchitodon, and the extremely enigmatic Kraterokheirodon known only from two teeth so unlike any known tetrapod alive or extinct it can only be classified as Amniota incertae sedis! Vancleavea was once in the same boat as all these creatures, known only by pieces of the skeleton and its armour, and with any luck, Acallosuchus and the other mystery creatures will end up like Vancleavea and turn up some complete skeletons one day.

Other: Vancleavea is known from throughout the Chinle Formation and several other localities in the southern US, however, most of these specimens consist of isolated bones and osteoderms. The Chinle Formation covers many tens of millions of years from top to bottom, and it’s unlikely the single species V. campi was that long-lived (its range spans a whole 20 million years!). Variations between some specimens suggest that there may be more diversity within Vancleavea then we currently recognise. However, until better specimens are found and can be compared, we can’t be sure how Vancleavea evolved and changed throughout the course of the Chinle.

Vancleavea has a fairly complicated history, the holotype was first discovered in the Petrified Forest by fossil collector Phillip Van Cleave, who lent it his name, but it wasn’t described and named until 1995 and still only consisted of a fragmentary skeleton. Nearly complete specimens from Ghost Ranch were discovered in 1982, but they wouldn’t be recognised as Vancleavea until decades later. In 2008, new specimens from the Petrified Forest were published, but Vancleavea still had to wait another year before the Ghost Ranch specimens were extensively described and its strangeness could be fully appreciated.

Until recently, Vancleavea was the only known stem-archosaur of its kind known in the world, and its relationship to other archosauriforms was enigmatic. However, the discovery of the closely related Litorosuchus from China indicates that the Vancleavea-family (“vancleaveans”) was indeed more diverse and widespread. Unlike Vancleavea, Litorosuchus was marine, and had a much longer, almost spinosaur-like snout. The position of Vancleavea in the archosauromorph tree is still uncertain, but it has been suggested to be a type of proterochampsian, a group of typically crocodile-like reptiles closely related to archosaurs proper. Particularly, it has been allied to the family Doswelliidae, a peculiar family of proterochampsians with similarly strange armour and skeletons. Regardless of where it truly belongs, Vancleavea is at least generally agreed to be a fairly derived archosauriform, quite close to the crown group of Archosauria, albeit having evolved down a very unusual, unique route all of its own.

~ By Scott Reid

Sources under the cut