#drepanosauridae

[alphynix]

Drepanosaurs were a weird little group of tree-climbing Triassic reptiles with prehensile claw-tipped tails, chameleon-like bodies, humped backs, grasping feet, long necks, and somewhat bird-like skulls that may have been tipped with toothless beaks in some species.

Recently some of them have been recognized as also having adaptations for digging and ripping into insect nests, similar to modern anteaters, with highly specialized forelimb bones and a massively enlarged hoked claw on each hand.

And now we have another one of these digging drepanosaurs: Unguinychus onyx, whose name delightfully translates to "claw claw claw"!

Living in what is now New Mexico, USA during the late Triassic, around 215-208 million years ago, Unguinychus is only known from its enlarged hand claws but was probably similar in size to some of its close relatives, likely around 40cm long (~1'4").

Based on skin impressions from the early drepanosaur Kyrgyzsaurus it also would have been covered in small scales, possibly with a skin crest and a chameleon-like throat sac.

Drepanosaurs' evolutionary relationships are rather unclear, with various studies classifying them as an early branch of diapsid reptiles, as close relatives of the gliding kuehneosaurids, or as protorosaurian archosauromorphs. But recently another idea has been proposed, instead placing them slightly further up the archosauromorph evolutionary tree in the allokotosaur lineage close to trilophosaurids – and notably making them very closely related to fellow Triassic bird-headed weirdo Teraterpeton.

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References:

Alifanov, V. R., and E. N. Kurochkin. "Kyrgyzsaurus bukhanchenkoi gen. et sp. nov., a new reptile from the Triassic of southwestern Kyrgyzstan." Paleontological Journal 45 (2011): 639-647. https://www.researchgate.net/publication/257843064_Kyrgyzsaurus_bukhanchenkoi_gen_et_sp_nov_a_New_Reptile_from_the_Triassic_of_Southwestern_Kyrgyzstan

Buffa, Valentin, et al. "‘Birds’ of two feathers: Avicranium renestoi and the paraphyly of bird-headed reptiles (Diapsida:‘Avicephala’)." Zoological Journal of the Linnean Society (2024): zlae050. https://doi.org/10.1093/zoolinnean/zlae050

Jenkins, Xavier A., et al. "Using manual ungual morphology to predict substrate use in the Drepanosauromorpha and the description of a new species." Journal of Vertebrate Paleontology 40.5 (2020): e1810058. https://www.researchgate.net/publication/344545876_Using_Manual_Ungual_Morphology_to_Predict_Substrate_Use_in_the_Drepanosauromorpha_and_the_Description_of_a_New_Species

Pugh, Isaac, et al. "A new drepanosauromorph (Diapsida) from East–Central New Mexico and diversity of drepanosaur morphology and ecology at the Upper Triassic Homestead Site at Garita Creek (Triassic: mid-Norian)." Journal of Vertebrate Paleontology (2024): e2363202. https://doi.org/10.1080/02724634.2024.2363202

[wtf-triassic]

Drepanosaurus unguicaudatus

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

Carroll, R. L. 1988. Vertebrate Paleontology and Evolution 1-698. 

Colbert, E. H. 1947. The little dinosaurs of Ghost Ranch. Natural History 59(9):392-399-427-428. 

Dalla Vecchia, F. M. 1991. Notes on the stratigraphy, sedimentology and paleontology of the Dolomia di Forni (Upper Triassic) of the Rio Seazza Valley (Preone, Friuli-Venezia Giulia)]. Gortania - Proceedings of the Friulian Museum of Natural History 12 (90) : 7-30. 

Irmis, R. B., S. J. Nesbitt, K. Padian, N. D. Smith, A. H. Turner, D. T. Woody, and A. Downs. 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317:358-361. 

Harris, J. D., A. Downs. 2002. A drepanosaurid pectoral girdle from the Ghost Ranch (Whitaker) Coelophysis Quarry (Chinle Group, Rock Point Formation, Rhaetian), New Mexico. Journal of Vertebrate Paleontology 111: 247 - 264. 

Pinna, G. 1979. Drepanosaurus unguicaudatus, nuovo genere e nuova specie di Lepidosauro del trias alpino. Atti della Societa Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano 121: 181 - 192. 

Pinna, G. 1986. On Drepanosaurus unguicaudatus, an Upper Triassic lepidosaurian from the Italian Alps. Journal of Paleontology 60 (5): 1127 - 1132. 

Pinna, G. 1988. Un nuovo esemplare giovanile di Drepanosaurus unguicaudatus del Norico di Val Preone (Udine) [A new juvenile specimen of Drepanosaurus unguicaudatus from the Norian of the Preone Valley, Udine]. Atti della Società Italiana di Scienze Naturali - Museo civico di Storia Naturale di Milano 128:80-84. 

Pinna, G., and S. Nosotti. 1989. Anatomia, morfologia funzionale e paleoecologia del rettile placodonte Psephoderma alpiunum Meyer, 1858. Memorie della Società Italiana di Scienze Naturali e del Museo Civico di Storia Naturale de Milano 25(2):1-50. 

Pritchard, A. C., S. J. Nesbitt. 2017. A bird-like skull in a Triassic diapsid reptile increases heterogeneity of the morphological and phylogenetic radiation of Diapsida. Open Science 4 (10): 170499. 

Renesto, S. 1994. The shoulder girdle and anterior limb of Drepanosaurus unguicaudatus (Reptilia, Neodiapsida) from the Upper Triassic (Norian) of Northern Italy. Zoological Journal of the Linnean Society 111 (3): 247 - 264. 

Renesto, S., J. A. Spielmann, S. G. Lucas, G. T. Spagnoli. 2010. The Taxonomy and paleobiology of the Late Triassic (Carnian-Norian: Adamnian-Apachean) drepanosaurs (Diapsida: Archosauromorpha: Drepanosauromorpha). New Mexico Museum of Natural History and Science Bulletin 46: 1 - 81. 

Senter, P. 2004. Phylogeny of Drepanosauridae (Reptilia: Diapsida). Journal of Systematic Palaeontology 2(3):257-268. 

Stefani, M., P. Arduini, A. Garassino, G. Pinna, G. Teruzzi, G. L. Trombetta. 1991. Palaeoenvironment of extraordinary fossil biotas from the Upper Triassic of Italy. Atti della Societa Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano 132 (24): 309 - 335. 

[infinitemachine]

Archosauromorph of the Day: Megalancosaurus Is Not Impressed by Eurwentala

Megalancosaurus Family: Drepanosauridae Time: Late Triassic Location: Italy Size (length): 25cm (10in) Note: Not a dinosaur. 

[alphynix]

Drepanosaurs were already some extremely weird animals, even among all the other weirdos of the Triassic period.

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.

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