#aetosaur

[fossilized-starlight]

Desmatosuchus 🌧️

[saritapaleo]

Archovember 2025 Day 4

Pseudosuchian Typothorax coccinarum, of Late Triassic, North America!

Our next archosaur, and our first pseudosuchian of this Archovember is Typothorax coccinarum! Pseudosuchians, the lineage that would eventually lead to crocodilians, dominated the Triassic, and did many of the things first that dinosaurs would do later on. Typothorax was an aetosaur, a unique group of pseudosuchians that evolved body armor similar to ankylosaurs. Typothorax was herbivorous, possessing small, leaf-shaped teeth, and had an upturned, shovel-like snout. Their forelimbs also seemed to be uniquely adapted to digging, suggesting they may have found food by rooting around in the soil for roots and tubers.

Typothorax coccinarum is known from the Late Triassic Chinle Formation of Arizona, as well as the Bull Canyon Formation of New Mexico and Texas. In the Chinle Formation, Typothorax would have lived alongside other aetosaurs like Rioarribasuchus and Scutarx, along with smaller pseudosuchians like Hesperosuchus and Revueltosaurus. It would have been preyed on by large rauisuchids like Postosuchus and Vivaron. Other archosaurs Typothorax could have seen in the Chinle Formation would have included lagerpetids like Dromomeron, allokotosaurs like Trilophosaurus, and dosweliids like Vancleavea. Dinosaurs were only just getting a foothold in the Late Triassic, and Typothorax could have come across early saurischians like Chindesaurus and Coelophysis. In the Bull Canyon Formation, the environment was similar, with the addition of the giant, beaked poposauroid Shuvosaurus, as well as the aetosaur Paratypothorax and the phytosaur Machaeroprosopus.

This art may be used for educational purposes, with credit, but please contact me first for permission before using my art. I would like to know where and how it is being used. If you don’t have something to add that was not already addressed in this caption, please do not repost this art. Thank you!

[knuppitalism-with-ue]

Results from the Flocking #paleostream!

Himalayasaurus, Typothorax, Lunataspis and Kunpengopterus.

[arminreindl]

Garzapelta: The Convergent Aetosaur

Our second pseudosuchian of 2024 couldn't be any more different from the first. While the first genus named this year was Varanosuchus, a small, agile atoposaurid from the Cretaceous, our second genus is Garzapelta (Garza County Shield), a large lumbering aetosaur, basically the ankylosaur of the Triassic.

If you remember the two posts on aetosaurs I did last year, you probably remember how osteoderms are super diagnostic for these guys and how the material doesn't need to be all that exciting to represent a new genus. In the case of Garzapelta its kind of an intermediate. It's better than the handfull of osteoderms we got for Venkatasuchus and Kryphioparma but its still mostly just osteoderms and some ribs (and a single toe bone).

Now the thing that stands out about Garzapelta is the specific combination of characters displayed by the osteoderms. So if you take a step back and look at aetosaurs as a whole, you'll see two big groups that split off from one another. The stagonolepoids, which eventually gave rise to the overly spiky desmatosuchines, and the aetosaurines, which gave rise to some really wide paratypothoracines. Shown below Desmatosuchus and Paratypothorax (not to scale), taken from Martz et al. 2013 and Heckert et al. 2010

But this doesn't yet say why Garzapelta is special. Well you see. We got both the paramedian osteoderms (the central two rows) and the lateral osteoderms (those spikes on the side). Now, the lateral osteoderms are morphologically really similar to those of desmatosuchines, HOWEVER, the paramedian osteoderms more closely resemble those of paratypothoracines. This is so extreme that when writing the paper, Reyes and colleagues did separate phylogenetic analysis for both osteoderm types. And as you might have guessed, when just looking at the laterals it was recovered as a desmatosuchine, but when looking at the paramedians it was recovered as a paratypothoracine (or rather something close to said groups). And when looking at both at the same time....well still a desmatosuchine.

Ironically, despite this, the authors don't think it was a desmatosuchine. Instead, the way the lateral and paramedian osteoderms connect is way more similar to paratypothoracines and ultimately the authors argue that its way more likely that the shape of the lateral osteoderms is the thing that evolved convergently. This whole situation does however highlight a major thing. Current datasets aren't really ready to deal with convergence like this.

And thats all I got to say about this one. Not as extensive as little Varanosuchus I know, but its surprisingly much given its just a bunch of osteoderms and not much in terms of skull remains or anything like that.

[saritawolff]

#Archovember Day 15 - Stagonolepis robertsoni

The Late Triassic aetosaurs were heavily armoured, terrestrial, herbivorous pseudosuchians (croc-line archosaurs), somewhat similar to the dinosaurian ankylosaurs that came much later. They were very successful, being the most abundant vertebrates in some environments. They came in a variety of shapes and sizes, from the large, spike-shouldered Desmatosuchus to the flattened, neck-spiked Typothorax to the tiny Aetosaurus ferratus. Some aetosaurs had a flattened, upturned, beak-like snout similar to pigs, which they probably used to dig for roots and tubers.

Stagonolepis robertsoni had one of the most extreme shovel snouts. It lived in Late Triassic Scotland and was a mid-sized aetosaur at around 2.5 metres (8 ft) long. Like other aetosaurs, it was covered in thick osteoderms covering the full length of its body. As it was fairly slow moving, this armour would have been necessary to repel attacks from other archosaurian predators of the time. It likely uprooted plants like horsetails, ferns, and the newly arrived cycads, chewing them with the peglike teeth at the back of its mouth. Stagonolepis’ front legs also seems to be adapted for “scratch digging,” which it would have employed to break through compacted soil before rooting around with its shovel snout.

Stagonolepis robertsoni lived in a sandy desert environment, and would have shared it with a variety of odd Late Triassic animals, including other pseudosuchians like Erpetosuchus and Ornithosuchus, early dinosauromorphs like Saltopus, early pterosauromorphs like Scleromochlus, rhyncosaurs like Hyperodapedon, and lizard-like parareptiles like Leptopleuron. No large predators (other than possibly Ornithosuchus) have been found in the Lossiemouth Sandstone Formation, but there must have been Carnian-era predators (likely large pseudosuchians) in Scotland for Stagonolepis’ armour to have been necessary, and they may be out there waiting to be found.

[arminreindl]

Venkatasuchus: Aetosaur from India

Once more I come bearing croc news. For the second time this year we are getting a new type of aetosaur, you know, those weird stem-crocodiles that somewhat converged with ankylosaurs? Yeah those guys. Much like Kryphioparma from just a few months ago, this new genus Venkatasuchus is a member of the Typothoracinae and known only from osteoderms. Thankfully, in the case of Venkatasuchus a lot more of them at least.

I mean sure 8 associated osteoderms plus the connected lateral elements is not that much, but it sure beats the few remains of Kryphioparma.

Anyhow, Venkatasuchus is from the middle Norian to Rhaetian stages of the Triassic of India, more specifically the Lower Dharmaram Formation in the east of the subcontinent. This is actually quite significant as aetosaurs are generally rare in Gondwanan parts of the world and the Dharmaram Formation actually has two: Venkatasuchus and an as of yet undescribed desmatosuchine. Furthermore, the formation actually represents a melting pot of Laurasian and Gondwanan fauna. The aetosaurs and phytosaurs are of Laurasian origin, but the dinosaurs of the formation are Gondwanan lineages.

Much to my surprise, there is ALREADY an illustration of this guy online courtesy of Scott Reid on Twitter, fantastic art, love how he cheekily hides the head and focuses on the armour.

Venkatasuchus - Wikipedia

Of course I jumped at the opportunity to write its wiki page, so far I do believe I managed to cover every new genus published this year.

[psie-smutki]

Late triassic aetosaur from Poland

Kocurypelta 🐽

[arminreindl]

Triassic Double Feature

Just weeks ago I remissed the lack of new croc taxa, seems I spoke to soon because they are being pumped out like crazy right now. For simplicity, I will cover two of the recent sorta-crocs together as neither are super extensive and they match in overall time.

These two new genera are the aetosaur Kryphioparma and the phytosaur Jupijkam. Pictured below the fossils of both with reconstructions of close relatives (art by Brian Engh and Gabriel Ugueto).

I'll start with Kryphioparma, which I wager is the less interesting of the two. Kryphioparma was an aetosaur, which are effectively early pseudosuchians that evolved a body type very similar to what nodosaurs did later. Heavily armored, sometimes with prominent spikes and herbivorous.

Kryphioparma is only known from four isolated and incomplete osteoderms, and though these are actually diagnostic and highly distinct, it does mean there's not super much to say. Hell, the scientific name literally means "mysterious shield" in reference to how little we know.

Regardless, scientists did determine two things. 1) It's a typothoracine aetosaur, narrowing down its placement to one of the two main branches. This means its closer related to Typothorax (with its armored cloaca) than to Desmatosuchus (with its shoulder spikes). 2) The second thing we know is that it wasn't alone. No, the localities that yielded its bones (Placerias Quarry and Thunderstorm Ridge) actually preserve a highly diverse aetosaur fauna, including Calypsosuchus, Tecovasuchus and two species of Desmatosuchus. All images by Jeff Martz.

Now the arguably more exciting find is that of Jupijkam, a type of phytosaur, which are archosaurs superficially resembling today's crocodiles. Now when I grew up, phytosaurs used to be considered to be entirely unrelated to crocs, being a type of archosaur believed to have diverged prior to the bird-croc split. However, it would appear that recent studies suggest that they could actually be true croc-line archosaurs, potentially being the earliest diverging group of Pseudosuchian.

Jupijkam is from the Rhaetian-Norian Blomidon Formation of Novia Scotia, Canada. This not only makes it one of the youngest, but also one of the northern-most known phytosaurs to date. It's scientific name, Jupijkam, is actually derived from the name given by the local Mi’kmaq people to their version of the horned serpent.

How Jupijkam is related to other phytosaurs is a bit wonky. Now generally, its recovered as a mystriosuchine, which isn't exactly a surprise given that most phytosaurs fall into this category. It's placement however shifts ever so slightly depending on the precise methods and characters used. 2/4 times it was found to be most closely related to Rutiodon (the phytosaur shown at the very start), once alongside the Indian Volcanosuchus and once to its exclusion. One tree simply results in a big polytomy which isn't really helpful, and one time it was found as a much more derived form related to Mystriosuchus. Whatever the case, additional finds both of other phytosaurs and Jupijkam specifically might clarify this in the future. Currently however, it seems that this form is not related to all the other American species of its time, suggesting it held out till the late Triassic independently. Which is pretty neat. Below you can see a comparisson between Jupijkam and some other slender-snouted phytosaurs, courtesy of Brownstein 2023. A is Jupijkam, B is Rutiodon and C is Machaeroprosopus

Really that wraps things up already, two new genera, both Triassic, both (potentially) early Pseudosuchians. A little bit out of my usual focus but very interesting none the less. Definitely gotta make another post soon since they just dropped yet another new one (a metriorhynchid), but I gotta read that paper first. Speaking of which A new aetosaur (Archosauria: Pseudosuchia) from the upper Blue Mesa Member (Adamanian: Early–Mid Norian) of the Late Triassic Chinle Formation, northern Arizona, USA, and a review of the paratypothoracin Tecovasuchus across the southwestern USA (escholarship.org) A late-surviving phytosaur from the northern Atlantic rift reveals climate constraints on Triassic reptile biogeography | BMC Ecology and Evolution | Full Text (biomedcentral.com) plus the respective Wikipedia pages Kryphioparma - Wikipedia Jupijkam - Wikipedia