#diapsid

[velochiocus-feather]

Dilophosaurs

Male + female

[ildarotyrannus]

Portrait of the diapsid reptile Youngina capensis from the Late Permian of the Karoo basin (South Africa). This is the second drawing in Paint after Vastatosaurus) Angina belongs to the Younginidae family, which was assigned to the order of the so-called Eosuchians, a group of small Permian-Triassic diapsids that became a wastebasket of not too closely related species. This reptile is known from several specimens, some of which were previously considered separate genera. Its anatomy combines features of primitive diapsids and more progressive groups. Being a small creature (the length of the skull is 5 cm with a total length of 30 cm), angina hunted insects in the shadow of the prevailing therapsids at that time.

Paint, 2024.

[alphynix]

Remarkably similar-looking gliding reptiles have appeared multiple different times over the group's evolutionary history, including the modern Draco – and despite being unrelated to each other almost all of them have achieved this in the exact same way, supporting their wing membranes on extremely elongated rib bones.

…Except for the weigeltisaurids.

These early members of the neodiapsid lineage were the very first vertebrates known to have experimented with gliding, all the way back in the late Permian period 260-252 million years ago. And while they superficially resembled all the later rib-gliders, their wings were actually something never seen before or since in a gliding reptile.

Basically, these animals were the closest that Earth life ever came to legitimately evolving a dragon.

Coelurosauravus elivensis here was a weigeltisaurid living in what is now Madagascar, which at the time was part of southern Pangaea. About 40cm long (1'4"), its body was adapted for a life climbing and gliding around in the treetops, with pneumatized air spaces lightening its bones and long slender limbs similar to those of modern tree-climbing lizards.

Its large wings were formed from around 30 pairs of long hollow rod-shaped bones extending out from the sides of its belly. These flexible structures could furl and unfurl with a motion like a foldable fan, and are thought to have been highly modified from osteoderms in the skin, creating an entirely new part of its skeleton. 

Towards the front of the wing the rods were arranged in several closely-packed "bundles", and one specimen of Coelurosauravus preserves an impression of what seems to be the outline of the wing membrane's leading edge – showing a stiffened pointed shape resembling the alula of a bird wing, which may have served a similar aerodynamic stabilization function.

[ From fig 2 in Schaumberg, G. et al (2007). New information on the anatomy of the Late Permian gliding reptile Coelurosauravus. Paläontologische Zeitschrift 81, 160–173. https://doi.org/10.1007/BF02988390 ]

But aside from the wings, the most striking feature of weigeltisaurids were their heads. Their skulls featured large crest-like frills resembling those of chameleons and ceratopsid dinosaurs, and their edges were adorned with prominent bumps and spikes. These were probably used for visual display and might have been a sexually dimorphic feature, with males having larger spikier crests than females. The crests may also have anchored large powerful jaw muscles, giving weigeltisaurids a wider gape and faster bite speed, helping them to snap up their fast-moving insect prey.

———

Nix Illustration | Tumblr | Pillowfort | Twitter | Patreon

[just9art]

Another selection of quick sketches done recently, longisquama, concavenator, smok, iguanodon, torvosaurus, stellasaurus, dilong, tauraspis, mei long and suminia more substantial content on the way soon, maybe

[wtf-triassic]

Longisquama insignis

By Tas Dixon

Etymology: Long Scales

First Described By: Sharov, 1970

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, ???

Time and Place: 242 million years ago, in the Ladinian of the Middle Triassic

Longisquama is known from the Madygen Formation of Kyrgyzstan

Physical Description: Longisquama was a small, somewhat lizard-like reptile reaching somewhere around 8 or 9 centimeters in body length from snout to tail - though this is uncertain, as tail elements are not preserved at this time. It had very large, hockey-stick shaped scales in a single row going along its back, with some of the longest scales being as long as the body of the animal - or longer, we really don’t have its tail. They go from somewhat long towards the head, reaching a peak length right after this, and then shrink in size as they go towards the tail - probably. Again, we don’t have a lot in terms of preserved elements of this animal, and while we know they were shaped like hockey sticks, there is a chance the fronds may have varied in size or shape or extended more on the back. They were attached to the spine by knob-like attachment points, similar to follicles for other integumentary structures like hair. There was probably soft tissue surrounding this follicle to keep the scale steady. The fronds had a raised ridge down the middle, with horizontal bars going up and down the length of the scale. The head of Longisquama was small, ending in a short point with tiny teeth inside, and it had a small head. It appears to have been quadrupedal - maybe, we don’t really have hind limbs - and with its legs splayed out to the side on its body. It was also quite skinny, based on the size of its ribcage. 

Diet: Longisquama was probably an insectivore, eating the variety of different insects that were present in its environment. 

Behavior: We really have no idea what the long scaled were used for. They were probably for display, nothing like feathers at all, and would have looked pretty to other Longisquama. They may have even been iridescent, much like many lizard scales, allowing them to display to each other in their deeply green and dense forested environment. There is no evidence that they would have been suitable as flying structures, and honestly beyond that we have no idea. There doesn’t seem to be evidence that they were used like Synapsid sails for cooling, either. Display is the best idea we have at this point. As for other behaviors, it probably would spend a good chunk of time in trees, and may have been social in doing so - the display structures do seem to imply a certain amount of social behavior. As far as parental care or other complex social structures, however, we have no evidence either way. 

Ecosystem: The Madygen was a deeply forested environment, with dense coniferous trees surrounding extensive lakes set in deep mud. This very wet and very green environment meant that there weren’t a lot of large animals present - instead, most of the animals were adapted for the trees and catching each other and plantlife among the branches. This extensively muddy and sticky environment means that a wide variety of animals - especially insects - were preserved well in the formation. Other creatures include the leg-glider Sharovipteryx; the Drepanosaur Kyrgyzsaurus; a mysterious probable-salamander Triassurus; a primitive cynodont Madysaurus; the Reptiliomorph Madygenerpeton; sharks such as Fayolia, Lonchidion, and Palaeoxyris; and many ray-finned fishes like Alvinia, Megaperleidus, Sixtelia, Ferganiscus, Oshia, and Saurichthys. As for insects, there too many to list: the earliest Hymenopterans (the group including wasps, bees, and ants); the great Titanopterans like Gigatian; moths, beetles, crickets, mosquitos, flies, grigs, and even mysterious Triassic insects with no close modern relatives. Seriously, you don’t want me to list them all - there’s hundreds of species on Fossilworks alone! So there was plenty for Longisquama to chow down on. 

Other: Oh Longisquama. Such a poorly preserved animal. Locked away in Russia, far away from the prying eyes of so many in this world. Unstudied, unloved. And yet, from the few photographs we have of its fossil, so many have insisted - insisted - we know exactly what it is. The enigmatic nature of Longisquama and it's completely poor fossil record (and, again, entrapment in Russia) have left it as a sort of Schrodinger’s Triassic Weirdo. What is it? What is it related to? What are those frond things? Does it play a role in the evolution of other groups? 

Here’s the thing, though. Longisquama is so poorly preserved and all we have are pictures of the fossil unless you want to go to Russia, badger some Russians, and look at the fossil - which very few people actually want to do. So, that having been said, we can’t use it for anything, basically, and we certainly can’t say anything about the fossil. 

We do know some things:

The long ribbons on Longisquama are not leaves it fell on top of. There are enough fossils of Longisquama to reinforce that it has these fronds every time, and they weren’t really shaped like any known plant leaves anyway. I know, it’s a bummer. 

It’s not a Dinosaur. It lacks Archosaur features, as far as we can tell from the fossil photos. So, if it’s not an Archosaur, it’s not a Dinosaur. 

It is not a Bird Precursor. While Longisquama - and quite a few other reptiles of the Triassic - convergently evolved similar facial features in the superficial sense to birds, they weren’t actually that similar on the skeletal level - they aren’t archosaurs! - and none of the rest of the skeleton resembles birds. Furthermore, we have one of the best transitional sequences ever known specifically for bird evolution - we have in the fossil record every step of the process from ancestral archosaur to bird, through the dinosaur family tree. The sheer number of feathered dinosaur fossils and other features found in dinosaurs such as similar hand configuration, body shapes, skeletal structures, and behaviors have left no doubt in the minds of the vast majority of scientists that birds are dinosaurs and, therefore, not descendants of Longisquama. 

It’s not a Pterosaur precursor. Literally all studies of its classification puts it far away from pterosaurs; furthermore, there are no clear links between Longisquama and the early pterosaurs of the Triassic period. While Pterosaur evolution isn’t quite as clear as bird evolution, we also have decent reason to believe pterosaurs are Archosaurs; meaning, Longisquama isn’t their ancestor. 

The fronds aren’t feathers. Even if feathers were that deep in terms of reptile ancestry that it was retained through many stages of evolution from Longisquama to early dinosaurs and pterosaurs, there is no evidence for this trait in living non-avian reptiles like Crocodilians (no, they don’t carry a feather gene, they just have the same protein that feathers are made out of) or Lizards, and thus the odds of these being weird pre-feathers is low. Instead, they are most likely highly modified scales. 

So, what is it? We don’t know. Maybe a Drepanosaur (more on those weirdos later). Maybe just a completely separate lineage of Triassic Weirdos. Probably an Archosauromorph? Maybe something else entirely? A Diapsid. We know it was a Diapsid. And that will have to be enough for now. 

~ By Meig Dickson 

Sources Under the Cut

Alifanov, V. R., and E. N. Kurochkin. 2011. Kyrgyzsaurus bukhanchenkoi gen. et sp. nov., a new reptile from the Triassic of southwestern Kyrgyzstan. Paleontological Journal 45(6):42-50. 

Fischer, J.; Voigt, S.; Schneider, J.W.; Buchwitz, M.; Voigt, S. (2011). "A selachian freshwater fauna from the Triassic of Kyrgyzstan and its implication for Mesozoic shark nurseries". Journal of Vertebrate Paleontology. 31 (5): 937–953. 

Ivakhnenko, M. F. 1978. Tailed amphibians from the Triassic and Jurassic of Middle Asia. Paleontological Journal 1978(3):84-89. 

Sharov, A. G. 1970. An unusual reptile from the Lower Triassic of Fergana. Paleontological Journal 1970(1):112-116. 

Sharov, A. G. 1971. Novye letayushche reptilii is Mesosoya Kazachstana i Kirgizii [New Mesozoic flying reptiles from Kazakhstan and Kirgizia]. Trudy Paleontologicheskiya Instituta Akademiy Nauk SSSR 130:104-113. 

SHCHERBAKOV, Dmitry (2008). "Madygen, Triassic Lagerstätte number one, before and after Sharov". Alavesia. 2 (5): 125–131. 

Tatarinov, L. P. 2005. A new cynodont (Reptilia, Theriodontia) from the Madygen Formation (Triassic) of Fergana, Kyrgyzstan. Paleontological Journal 39:192-198. 

Unwin, D. M., V. R. Alifanov, and M. J. Benton. 2000. Enigmatic small reptiles from the Middle-Late Triassic of Kirgizstan. In M. J. Benton, M. A. Shishkin, D. M. Unwin, E. N. Kurochkin (eds.), The Age of Dinosaurs in Russia and Mongolia. Cambridge University Press, Cambridge 177-186

[neat-deadandlive-things]

Tuatara skulls are truly beautiful.

Dead thing fact: Tuataras are unique in having a true diaspsid condition. They have two clear skull fenestras.

Juveniles also have a third eye on the top of their heads that remains somewhat functional in adults.

[archtangential]

Typical. Northern Alligator Lizards, Elgaria coerulea, have been biting me for 2 decades. This one is a younger adult, apparently already through its first tail loss, and caused no pain. Larger inds. can draw light blood. Generally lethargic. The blue fuzz on its mouth is from the old packing blanket it was disturbed from under. Eats arthropods, sometimes smaller lizards/verts like you'd expect. Alligator lizards are consistently outnumbered by the more active and agile fence lizards in my yard, but have maintained a consistent littoral presence of a least several inds. in the general area at a time for as long as I remember. I have however witnessed and photographed at least a couple of occasions of these #squamates climbing to the top of shrubbery to sun. #lizardsofinstagram #anguidae #anguimorpha #alligatorlizard #alligator #socal #bernie2020 #diapsid #eattherich (at Oceanside, California) https://www.instagram.com/p/B9aZhSMg-r1/?igshid=xqe4pj2j220h

[alithographica]

Science Fact Friday: A skull classification system that works all of the sometimes.

This is an example of why evolutionary trees get reorganized fairly often. Until recently it was believed that turtles were anapsids. Molecular studies indicate that they’re actually diapsids who lost their fenestra so they just /look/ anapsid. With our spotty fossil record, morphology isn’t always reliable – but sometimes it is. Some of the first evidence that birds are dinosaurs was based on skull studies. Likewise, it helped separate ancient proto-mammalian and non-mammalian reptiles. Like most tools, it’s best used in combination with other techniques.

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Transcript below the cut.

Skull Classification *in early amniotes

The rise of terrestrial animals required the evolution of an egg capable of being laid on dry land. These animals are called “amniotes”. This is in contrast to fish and amphibians, whose eggs must be laid in water.

There are four general skull types seen in early amniotes. Each skull represents a different branch of animals and is classified by the number of temporal fenestra (holes in the skull behind the eye). There is still debate over the function of the temporal fenestra, but many believe the holes allow for more mobile jaw muscles.

[Illustration of a general skull with no holes behind the eye socket]

Anapsid. No temporal fenestra. The most basic amniotic skull. Modern turtles have anapsid skulls but are probably actually descended from diapsids whose fenestra closed.

[Arrow to another general skull with one low hole behind the eye socket]

Synapsid. A single temporal fenestra. Seen in extinct, mammalian-ancestor reptiles. Modern mammals are synapsids but no longer have temporal fenestra.

[Arrow from anapsid skull to another skull with two holes behind the eye socket, one over the other]

Diapsid. Two temporal fenestra. Seen in Lepidosaurs (snakes, lizards) and Archosaurs (birds, crocodilians, dinosaurs). Modern birds, lizards, and snakes have modified fenestra, but the diapsid condition can still be easily seen in tuatara and alligators.

[Arrow from diapsid skull to another skull with one high hole behind the eye socket]

Euryapsid. A single temporal fenestra like a synapsid, but positioned higher. Debated classification, as the euryapsid condition probably evolved multiple times and can therefore be seen in unrelated animals. Seen in extinct aquatic reptiles like Ichthyosaurs and Plesiosaurs.

References: http://www2.fiu.edu/~longoria/gly1101/Mz-reptiles.htm

http://tolweb.org/accessory/Temporal_Fenestration_of_Amniotes?acc_id=463