#archosauriforms

[agiantshark]

Vancleavea campi is wonderfully weird, so it, of course, deserves a quick drawing :)

[saritawolff]

Whelp we’ve got about a week and a half til November (aaaaaah), so I guess I’ll post this year’s Archovember list now!

It’s a bit dinosaur-heavy this time, but there are a lot of species I’d really like to try my hand at! Also, we have two leptoceratopsians and two Araripesuchus species. I thought it would be interesting to compare and contrast these species within the same month, so I hope it doesn’t get /too/ repetitive!

For new folks: this is my “Draw Dinovember” list that I expanded out to include other archosauriforms. I started doing this a few years ago to challenge myself to draw species I’ve never drawn before and/or ones that don’t get a lot of attention. Feel free to join in! You can do the whole list, just the dinosaurs, just the pterosaurs, just the pseudosuchians, just your favorites, just ones you’ve never drawn before, roll a D20 and a D10 and draw the sum of whichever numbers you get, etc. Just make sure they’re posted on or after their specific day so I remember to share them on my blog! You can use #Archovember or #Archovember2023, as those are the tags I follow. (Note that I and the whole Archovember event are usually a lot more active on Instagram so if you have an IG I encourage you to join in there!)

Anyway, here is the list in case the graphic is hard to read:

1. Your Choice!

2. Furcatoceratops elucidans

3. Tupandactylus navigans

4. Deinosuchus hatcheri

5. Herrerasaurus ischigualastensis

6. Lewisuchus admixtus

7. Supersaurus vivianae

8. Zhejiangopterus linhaiensis

9. Dynamosuchus collisensis

10. Megalosaurus bucklandii

11. Macrospondylus bollensis

12. Miragaia longicollum

13. Dorygnathus banthensis

14. Leptoceratops gracilis

15. Stagonolepis robertsoni

16. Shantungosaurus giganteus

17. Paleorhinus bransoni

18. Cascocauda rong

19. Kelenken guillermoi

20. Prestosuchus chiniquensis

21. Yangchuanosaurus shangyouensis

22. Istiodactylus latidens

23. Kunbarrasaurus ieversi

24. Araripesuchus wegeneri

25. Tylocephale gilmorei

26. Ixalerpeton polesinensis

27. Udanoceratops tschizhovi

28. Tapejara wellnhoferi

29. Araripesuchus rattoides

30. Scutellosaurus lawleri

One last note, and a warning I usually issue to new paleoartists: while looking for references for these species you’ll come across David Peters. His references tend to dominate search results when looking for less well-known species. They are also highly inaccurate, even the skeletals. So make sure you omit “The Pterosaur Heresies” and “Reptile Evolution” from your google search. If you have issues finding references, let me know and I can share what I’m using!

[catella-ars]

Belatedly finished @saritawolff 's Archovember

https://saritawolff.tumblr.com/post/731715077418385409/whelp-weve-got-about-a-week-and-a-half-til

[alphynix]

Proterochampsids were a group of Triassic archosauriformes, closely related to the true archosaurs (crocodilians, pterosaurs, and dinosaurs/birds).

Known only from South America between about 242 and 205 million years ago, these reptiles' heads were wide at the back but very narrow along the snout, often with prominent bony bumps and ridges on their skulls, and they had less osteoderm armor on their bodies than other archosauriformes.

They've traditionally been interpreted as very crocodile-like and semi-aquatic, but their long slender limbs and presence in rather arid paleoenvironments suggest they may have been more terrestrial fast-running predators.

Tropidosuchus romeri here lived about 235 million years ago in what is now Argentina. It was one of the smaller proterochampsids, only about 50cm long (1'8"), with just a single row of osteoderms along its back, and had larger and lower-set eyes compared to its relatives.

CT scans of its braincase indicate it had a particularly good sense of smell, and it may have relied mainly on scent to locate prey.

———

NixIllustration.com | Tumblr | Twitter | Patreon

[roygattero]

Ischigualasto series, alternate takes:

Proterochampsa chasing Trialestes, black and grey watercolor, 2023

[faunalregion]

[ddhoneyboy]

Please look at my dino-puppies

They are Erythrosuchids and just.. just look at them. With the huge heads and short lil legs

And sure they are apex predators and one of them is insanely large but… dino puppy.. baby shaped.. look like pitbulls..

(The amazing artists are credited in alt text, if you can find the artist for the last image please tell me!)

[confusedhadrosaur]

Day 14:  Proterosuchus fergusi

[justgoji]

Erythrosuchus africanus from memory. How well did I do guys?

Yes I drew this on my geometry packet, math is freaking boring and I’m tired of pretending it’s not.

[a-dinosaur-a-day]

Birds are class Aves.

Sure, under Linnaean taxonomy. But, well,

A) Linnaeus was a eugenecist so his scientific opinions are suspect and his morality is awful

B) he didn't know about evolution

C) he didn't know about prehistoric life

so his classification system? Sucks ass. It doesn't work anymore. It no longer reflects the diversity of life.

Instead, scientists - almost across the board, now - use Clades, or evolutionary relationships. No rankings, no hierarchies, just clades. It allows us to properly place prehistoric life, it removes our reliance on traits (which are almost always arbitrary) in classifying organisms, and allows us to communicate the history of life just by talking about their relationships.

So, for your own edification, here's the full classification of birds as we currently know it, from biggest to smallest:

Biota/Earth-Based Life

Archaeans

Proteoarchaeota

Asgardians (Eukaryomorphans)

Eukaryota (note: Proteobacteria were added to an asgardian Eukaryote to form mitochondria)

Amorphea

Obazoa

Opisthokonts

Holozoa

Filozoa

Choanozoa

Metazoa (Animals)

ParaHoxozoa (Hox genes show up)

Planulozoa

Bilateria (all bilateran animals)

Nephrozoa

Deuterostomia (Deuterostomes)

Chordata (Chordates)

Olfactores

Vertebrata (Vertebrates)

Gnathostomata (Jawed Vertebrates)

Eugnathostomata

Osteichthyes (Bony Vertebrates)

Sarcopterygii (Lobe-Finned Fish)

Rhipidistia

Tetrapodomorpha

Eotetrapodiformes

Elpistostegalia

Stegocephalia

Tetrapoda (Tetrapods)

Reptiliomorpha

Amniota (animals that lay amniotic eggs, or evolved from ones that did)

Sauropsida/Reptilia (reptiles sensu lato)

Eureptilia

Diapsida

Neodiapsida

Sauria (reptiles sensu stricto)

Archelosauria

Archosauromorpha

Crocopoda

Archosauriformes

Eucrocopoda

Crurotarsi

Archosauria

Avemetatarsalia (Bird-line Archosaurs, birds sensu lato)

Ornithodira (Appearance of feathers, warm bloodedness)

Dinosauromorpha

Dinosauriformes

Dracohors

Dinosauria (fully upright posture; All Dinosaurs)

Saurischia (bird like bones & lungs)

Eusaurischia

Theropoda (permanently bipedal group)

Neotheropoda

Averostra

Tetanurae

Orionides

Avetheropoda

Coelurosauria

Tyrannoraptora

Maniraptoromorpha

Neocoelurosauria

Maniraptoriformes (feathered wings on arms)

Maniraptora

Pennaraptora

Paraves (fully sized winges, probable flighted ancestor)

Avialae

Avebrevicauda

Pygostylia (bird tails)

Ornithothoraces

Euornithes (wing configuration like modern birds)

Ornithuromorpha

Ornithurae

Neornithes (modern birds, with fully modern bird beaks)

idk if this was a gotcha, trying to be helpful, or genuine confusion, but here you go.

all of this, ftr, is on wikipedia, and you could have looked it up yourself.

[manusuchus]

Vancleavea campi at the bottom of a river.

An extrange semi-aquatic non-archosaurian archosauriform from the Late Triassic of North America.  

[harpagornis]

Did phytosaurs have lips?

Mystriosuchus planirostris by @paleoart, the inspiration for this post.

2016 was many things, but one of the best was definitely being the call out year for many archaic paleoartist mistakes. One of these was the absence of lips in many reconstructions, from the skin-wrapped maws of theropod dinosaurs to the bare-toothed saber-toothed cats to the rather ridiculous depictions of entelodonts and other prehistoric mammals as fanged demons. This year saw the publication of various papers showing that teeth do generally in fact need lips to be protected from damage and moistened, meaning that many animals traditionally reconstructed as bared-toothed monsters need a healthy amount of oral tissue.

That said, things aren’t black and white. Crocodilians, after all, still have bare teeth. In one of these papers, Larson et al 2016, it’s been suggested that their aquatic habits compensate for their lack of lips, as humidity certainly isn’t a problem. However, as the Mark Witton link above informs you, many crocodiles go through prolonged periods of life on land without tooth degradation. It also doesn’t cover how terrestrial crocodylomorphs would have coped with the absence of lips, or why many aquatic vertebrates like dolphins (Platanista aside) still kept their lips.

It seems, therefore, that crocodiles are simply off in this regard. Their liplessness actually appears to derived from a highly unusual facial development process, which essentially renders their entire face a single “scale”. This seems to have evolved in order to develop the extensive Integrumentary Sense Organs (ISOs), thinning the facial skin in order to increase sensivity, and it carried over into their terrestrial descendants.

This obviously raises the question of whereas groups similar ecologically and morphologically to aquatic crocodilians underwent a similar process. Where they also lipless, or did they in fact retain their lips, making comparisons to crocodiles all the more questionable?

The Phytosaurs

​

Phytosaur head diversity by Darren Naish. Taxa included: Smilosuchus gregorii, Pravusuchus hortus, Mystriosuchus westphali, Paleorhinus bransoni and Pseudopalatus pristinus.

Phytosaurs were, in some respects, the “original crocodiles”, having evolved and prospered long before crocodylomorphs ever touched the water. Although they weren’t particularly closely related (birds are closer to crocodiles than phytosaurs are), these archosauriform reptiles did hit most of the same notes as crocodiles: barrel-shaped bodies, extensive osteoderm armours (in some cases even better protected, due to the bell-shaped cap on the throat and various scutes on the forelimbs and belly), generally short limbs and large, paddle-like tails.

While some phytosaurs explored odd ecological niches – Nicrosaurus and similar taxa are adapted to a primarily terrestrial lifestyle,  while Mystriosuchus was inversely so specialised to life in the water that it was practically the Triassic Metriorhynchus -, a generally semi-aquatic lifestyle for most phytosaurs can be inferred due to due sheer prevalence in freshwater and shallow marine deposits, limb proportions and shape, laterally flattened and powerful tails and retracted nostrils (though keep reading).

Various tracts attributed to these animals similarly imply a close functional match between phytosaurs and crocodiles. Various swimming tracts have been attributed to phytosaurs, while the Apatopus footprints show an interesting insight on these animals’ terrestrial locomotion capacities, being capable of an erect gait like archosaurs and mammals, including modern crocodiles and alligators. Paleopathology studies indicate similar behaviours such as interspecific biting (hence the need for strong armour), and perhaps more damningly endocast studies show that the general phytosaur brain shape was rather similar to that of modern crocodilians (albeit with a few differences, like the size of the brain and the presence of multiple sinuses; see below).

For all intents and purposes, phytosaurs were functionally crocodilian, offering one of the most extreme cases of convergent evolution ever recorded. But no matter how close, phytosaurs were still off the mark in various ways.

Phytosaur facial anatomy and morphology

Pseudopalatus buceros skulls, exemplifying the general morphology of phytosaur skulls as well as interspecific variation. Notice massive premaxila.

The most classical thing you’ve ever heard about phytosaurs was how they differ from crocodiles in having the nostrils be close to the eyes/on top of the head rather than at the tip of the snout. This is true; as you can see, the nostrils are located in front or above the eyes in a “volcano-like” elevation; combined with the nostril-less and often conical snouts, this gives them a distinctive dolphin-like profile.

Like in cetaceans, this nostril placement would come in handy on a mostly aquatic lifestyle, avoiding drag and allowing the animal to surface only a small part of the head and remain concealed underwater. However, unlike cetaceans – and marine reptiles such as plesiosaurs -, this nostril position is not derived from nasal retraction. In fact, phytosaur nostrils are sometimes noted as being rather protracted, sometimes as a result of the general elevation of the nasal region.

Instead, what happened is that phytosaurs elongated the premaxila at the expense of the other skull bones. Unlike crocodiles – and whales and plesiosaurs and many other aquatic tetrapods -, half or more of the phytosaur upper jaw is composed of a single bone, normally a vestige at the end of the jaw in most amniotes, that expanded radically. This hints at a pretty rapid elongation of the snout, explaining maybe why long-snouted phytosaurs appear “out of nowhere” in the fossil reccord.

Predictably, this could also hint at rather atypical development, which is etremely important in dictating the presence or absence of lips.

Another frequently cited difference is the presence of antorbital fenestrae. These are the famous “holes” in front of the eyes present in most dinosaurs and other archosauriform reptiles. Crocodiles have lost them, but they are present in phytosaurs, though they can be reduced in some species. Perhaps associated with this, phytosaurs also have extensive antorbital sinuses, while crocodilians lack them altogether. Phytosaurs also have an extensive premaxillary sinus, though as crocodilians have most of their snout taken by the nasal airways this may not make a lot of difference.

With a few exceptions, most aquatic crocodilians have conical teeth; they compensate for the lack of meat-cutting speciations with the infamous “death-rolls”. Phytosaurs, by contrast, generally have serrated teeth, and combined with the presence of crests on many specimens it seems unlikely that these animals engaged in “death-rolls”, instead opting for more typical meat-eating behaviours. To date longirostrine phytosaurs are the only “gharial-like” vertebrates with serrated teeth, and it might explain why they were frequently associated with the carcasses of terrestrial vertebrates like rhynchocephalians and dinosaurs.

Unlike the teeth of crocodiles, phytosaur teeth seem to be rarely interlocked. Even without lips, it seems likely that the upper jaw teeth covered the lower jaw ones.

What about the lips?

​

Leptosuchus skull, illustrating the basic points for and against phytosaur lips. For are in red: anteorbital fenestra and serrated teeth. Against are in green: long prexmaxila, POSSIBLE ISOs, front teeth POSSIBLY too large to fit within lips. The latter two are of course ambiguous.

With the above in mind, the absence for or against phytosaurian lips is…mixed.

The rapid premaxilary development in phytosaurs is the key to understanding how the jaw integument of these animals worked. It is possible that the premaxila’s growth prevented the formation of conventional lips, either due to physical and metabolic constraints or because the same genes triggering it could have prevented the development of lips. Perhaps the same pressures causing the crocodilian “single scale” would have been forced on phytosaurs by this developmental quirk.

On the other hand, other parts of the phytosaur skull anatomy seem to suggest the presence of lips:

The aforementioned antorbital fenestrae suggests that the phytosaur skull was less “skin-tight” than that of crocodilians. In modern birds, the only living reptiles with antorbital fenestrae, that area of the skull is covered by various soft tissues, and indeed areas of the avian beak devoid of a rhamphotheca tend to be covered by fleshy lips.

Serrated teeth tend to be more vulnerable than conical teeth to degradation, so most predatory animals that possess them have them covered by lips. The only crocodilians with clearly serrated teeth are terrestrial species and the fairly basal thalattosuchians, which are still on the limbo on whereas they had lips or not.

It is possible that phytosaurs found themselves in an unique integumental arrangement. Perhaps they did become lipless, with a “single scale” covering the jaws, while the rest of the head had a more normal integument.

A deciding factor in this argument would be the discovery of ISOs on phytosaur jaws. However, structures associated with these organs, such as pits, are rarely discussed outside of the context of pathology when it comes to these animals. There is plenty of literature on pits and holes in phytosaur skulls being caused by fights and bites, but few on any possible natural ones.

Conclusion

​

Modern Ganges River Dolphin. Although it has exposed teeth, it’s also not the norm among cetaceans.

Just because something resembles another doesn’t mean that there is an exact equivalency. Case in point: no matter how close phytosaurs got to crocodilians, they still differed in many aspects, and could not be mistaken for them in life.

It’s clear that skin-wrapping is a tremendous lack of appreciation for the organic nature of extinct animals. The lack of lips in crocodilians has been taken far too long to be the “norm”; but, as it turns out, it is an anomaly among the usual amniote tendencies.

We may never know for sure whereas phytosaurs had lips or not. Hell, it’s even possible that some had while others went full Platanista. However, far too often are they taken to be crocodile-like for granted, without other possibilities, equally as valid as they are, taking into consideration.

Hopefully, further research will grant us insights on how these already spectacular animals looked in life.

References:

Reisz, R. R. & Larson, D. (2016) Dental anatomy and skull length to tooth size rations support the hypothesis that theropod dinosaurs had lips. 2016 Canadian Society of Vertebrate Paleontology Conference Abstracts, 64-65.

Grigg, G., & Kirshner, D. (2015). Biology and evolution of crocodylians. Csiro Publishing.

Soares, D. (2002). Neurology: an ancient sensory organ in crocodilians. Nature, 417(6886), 241-242.

Stocker, M. R. & Butler, R. J. 2013. Phytosauria. Geological Society, London, Special Publications 379, 91-117.

Kimmig, J. 2013. Possible secondarily terrestrial lifestyle in the European phytosaur Nicrosaurus kapfii (Late Triassic, Norian): a preliminary study. Bulletin of the New Mexico Museum of Natural History and Science 61, 306-312.

Gozzi, E. & Renesto, S.A. 2003. Complete specimen of Mystriosuchus (Reptilia, Phytosauria) from the Norian (Late Triassic) of Lombardy (Northern Italy). Rivista Italiana Di Paleontologia e Stratigrafia 109(3): 475-498.

Michelle R. Stoker; Sterling J. Nesbitt; Li-Jun Zhao; Xiao-Chun Wu; Chun Li (2016). “Mosaic evolution in Phytosauria: the origin of long-snouted morphologies based on a complete skeleton of a phytosaur from the Middle Triassic of China”. Society of Vertebrate Paleontology 76th Annual Meeting Program & Abstracts: 232.

[saritawolff]

#Archovember Day 9 - Doswellia kaltenbachi

Hailing from Late Triassic North America, Doswellia was an archosauriform relative of the crocodile-like Proterochampsids. Together with the proterochampsids, Doswelliids formed an ancient group outside of Archosauria and, unlike the Archosaurs, have no living representatives to this day.

From neck to tail, Doswellia was heavily armored in rows of bony scutes (which make it just SO fun to draw /sarcasm). Unlike crocodiles, which have a strong bite force but a much weaker ability to open their jaws, Doswellia had strong jaw muscles for both closing and opening their jaws in a scissor-like motion. It’s sharp teeth and upward-pointing eyes seem to suggest that Doswellia was at least a semi-aquatic predator. It may have hunted on land as well, partially burrowing itself with only its armoured back exposed for defense. Possible food sources include small reptiles, crustaceans, mollusks, or even large insects.

Doswellia kaltenbachi would have shared its environment with other Late Triassic North American animals, such as cynodonts, crocodyliformes, temnospondyl amphibians, Redfieldiid fish, and the freshwater shark Lissodus.

Bonus:

[prehistorichumanetal]

Megapnosaurus

Etymology: Big Dead Lizard

Length: 3 meters ( 3 m )

Height: 80 centimeters ( 80 cm )

Weight: 32 kilograms ( 32 kg )

Diet: Carnivore

Temporal range: Early Jurassic, Mesozoic Era ( 199 million years ago - 188 million years ago )

Place: Africa ( Zimbabwe · South Africa )

Classification: Life, Animalia, Chordata, Vertebrata, Gnathostomata, Tetrapoda, Amniota, Sauropsida, Reptilia, Diapsida, Neodiapsida, Sauria, Archosauromorpha, Archosauriformes, Archosauria, Avemetatarsalia, Ornithodira, Dinosauromorpha, Dinosauriformes, Dracohors, Dinosauria, Saurischia, Theropoda, Neotheropoda, Coelophysoidea, Coelophysidae, Coelophysinae

[alphynix]

It Came From The Wastebasket #15: Rauisuchian Revolution

Pseudosuchians, or "croc-line archosaurs", are one of the two major lineages of archosaur reptiles, alongside the avemetatarsalians (pterosaurs and dinosaurs). Although today they're represented only by crocodilians, they were especially successful and diverse back in the Triassic – and it was only after a mass extinction took out most of them that the dinosaurs were able to rise to prominence for the rest of the Mesozoic Era.

A grouping of pseudosuchians traditionally known as "rauisuchians" had upright limbs in a distinctive "pillar-erect" hip arrangement. Many of these croc-relatives were large quadrupedal predators, but others developed bipedal theropod-like postures, with some so remarkably convergent that they were initially misidentified as ornithomimosaurs.

The first rauisuchians were discovered in the 1930s, represented only by fragmentary remains, and while they were initially recognized as being pseudosuchians their exact evolutionary relationships within that group were poorly understood for a long time. Over the next several decades they were classified with aetosaurs (early armored pseudosuchians), then ornithosuchids (even earlier pseudosuchians), and then erythrosuchids (not even pseudosuchians but an earlier type of archosauriform).

More complete fossil discoveries and better cladistic analysis methods in the 1980s led to them being classified as being very closely related to crocodylomorphs, with three main lineages recognized: the prestosuchids, the rauisuchids, and the poposauroids.

The "prestosuchid" Prestosuchus chiniquensis, the rauisuchid Postosuchus kirkpatricki, & the poposauroid Effigia okeeffeae (not to scale)

But even by the end of the 20th century "Rauisuchia" had never actually gotten a formal definition, and it had very much become a wastebasket taxon for a variety of paracrocodylomorph pseudosuchians that didn't easily fit into any other major lineages.

In the 2000s renewed interest in rauisuchians' anatomy and evolutionary relationships led to increasing recognition that they weren't even a single defined group, with various species instead falling into different points along an "evolutionary grade". The poposauroids and rauisuchids still seem to be distinct lineages, but the "prestosuchids" were found to be polyphyletic, with some forming a grade between the other two "rauisuchid" groups and others turning out to not even be paracrocodylomorphs.

And although the taxonomic concept of "Rauisuchia" as a distinct group has now been abandoned, the term "rauisuchians" does still remain in common use as an informal name for these animals – probably because it's much more concise than saying "non-crocodylomorph paracrocodylomorphs".

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Nix Illustration | Tumblr | Twitter | Patreon

[roygattero]

Ischigualasto series, alternate takes:

Proterochampsa chasing Trialestes, ballpoint pen, 2023