#neosuchia

[arminreindl]

Varanosuchus: First Fossil Croc of 2024

We are two weeks into the year and we already had a bunch of big croc papers, so today I'll cover the first of the two new genera named so far. Varanosuchus sakonnakhonensis (Monitor lizard crocodile from Sakon Nakhon) is a small atoposaurid neosuchian from the Early Cretaceous of Thailand, a country that has seen a virtual boom in croc papers this past year between the description of Alligator munensis and Antecrocodylus.

Varanosuchus was a small animal, maybe a meter in length if a little longer with a notably short and deep skull and long slender limbs revealing it to have been at least somewhat terrestrial. We actually have a decent amount of material of this guy. The holotype consists of a 3 dimensionally preserved skull as well as assorted postcranial remains (vertebrae, ribs, osteoderms and limbs), there is a second skull of whats likely to be a differently aged individual also showing a 3D skull and well the third ones just a skull table but 2/3 is still great.

Now this guy was an atoposaurid, which is a group of crocodylomorphs that lived from the Jurassic to the end of the Cretaceous, their last members existing on the island of Hateg some 66 million years ago. Atopsaurids were generally small animals with short snouts and longish legs. Some examples of atoposaurids include Knoetschkesuchus from Germany, Aprosuchus from Romania and Alligatorellus from France and Germany, all three pictured below, art by @knuppitalism-with-ue

Now the matter of ecology for atoposaurids in general and Varanosuchus in particular is not clear. Altirostral skulls such as that of Varanosuchus are generally associated with terrestrial crocodylomorphs as best examplified by notosuchians. Their teeth and size both obviously speak against being shoreline ambush predators like modern crocs and their legs are straight and slender, suggesting they had an erect posture and not the more sprawling one seen in semi-aquatic forms. Though they could have still had some aquatic affinities. The authors for instance argue that the osteoderms, having plenty of pits, are more like those of an animal that spends time in the water and would thus use them in thermoregulation. So maybe they did enter water from time to time, somewhat like some modern lizards, tho I think its fairly certain that they spend a decent amount of time on land. The artwork below is the reconstruction from the paper itself.

Another matter discussed in the paper is phylogeny, more precisely the relationship of Neosuchians and how Eusuchia is defined. On the first front, its worth noting that the paper recovered both atoposaurids and paralligatorids as monophyletic groups and had them be each others closest relatives, a notion that has been recovered before. More interesting perhaps is the fact that the next closest relatives to these two were hylaeochampsids and Bernissartia, which are typically recovered closer to modern crocs. Which in fact form a separate branch that is the sister group to all the afforementioned clades and taxa. And then you got goniopholids, dyrosaurs and pholidosaurs which are all more basal than the paralligatorid+atoposaurid+crocodilian group, which is back to the ordinary really. The second thing is the definition of Eusuchia. So for the longest time Eusuchia has been defined to include those Neosuchians that have choanae that are fully enclosed by the pterygoid bones (I know I know a bunch of anatomy stuff bear with me). So if the choanae was surrounded by the pterygoid, its an Eusuchian, if not, its more basal. Well, atoposaurids don't have that....BUT VARANOSUCHUS DOES. This, coupled with hylaeochampsids also having this feature and being recovered closer to atoposaurids than to Crocodilians basically suggests that the feature is not diagnostic for Eusuchia and instead appeared multiple times independently.

Moving away from anatomy and phylogeny and all that stuff, I think its very cool that croc research in Thailand has kinda picked up this last year. And fittingly enough some people have even worked on a short documentary covering the known diversity of pseudosuchians from Thailand, giving an overview over the named forms from the Jurassic to today, from titans like Chalawan to even these newest dwarf forms. While the narration is obviously in Thai, there are English subs and I highly recommend looking into it (even if I disagree with their depiction of Varanosuchus as arboreal, its perhaps overshooting the goal a little bit).

Finally here's the paper itself (tho paywalled) New Cretaceous neosuchians (Crocodylomorpha) from Thailand bridge the evolutionary history of atoposaurids and paralligatorids | Zoological Journal of the Linnean Society | Oxford Academic (oup.com) and the wikipedia page I've been working on Varanosuchus - Wikipedia

I'll try to write up a post on the other new genus, Garzapelta, later this weekend so stay tuned for that.

[paleonativeart]

Day 14: Indosinosuchus

An teleosaurid neosuchian that swim throughout the shallow rivers during the wettest season of late Jurassic or Early Cretaceous period.

[extinctworld-ua]

Shamosuchus

Shamosuchus — вимерлий рід неозухієвих крокодилоподібних, що мешкав у пізньокрейдяному (кампан) періоді на території Джадохтинської формації в Монголії, приблизно 75-71 мільйон років тому.

Повний текст на сайті "Вимерлий світ":

https://extinctworld.in.ua/shamosuchus/

[arminreindl]

Two lovely crocs in this one, there's the medium-sized (2-2.5 meter) Confractosuchus which we know for a fact ate dinosaurs (based on the fact that we found an ornithopod in its stomach). And on the right there's Isisfordia which probably only grew up to a meter in length. Both are Neosuchians, tho its not entirely certain how they relate to modern forms, with papers sometimes featuring them within Eusuchia and sometimes outside of it.

And so here is the result of the Winton Formation stream!

Home of Australovenator, a bunch of sauropods and lots of other critters. Preserved in this formation are the animal of a coastal river system.

Have some detail shots as well

[confusedhadrosaur]

Day 24: Burkesuchus mallingrandensis

[alphynix]

While modern crocodilians are all semi-aquatic, their Mesozoic ancestors (known as neosuchians) started off fully terrestrial, only really moving into their familiar water-based ecological niches around the mid-Jurassic when the dinosaurs were dominating on land.

But on multiple occasions members of the neosuchian croc lineage independently went back to fully terrestrial habits, and Tarsomordeo winkleri here is one of the most recently discovered examples.

Living about 113 million years ago in the Early Cretaceous of central Texas, USA, Tarsomordeo was surprisingly small, only about 60cm long (2′) -- the size of an average cat. Its tiny size even ended up inspiring its name, which translates to “ankle biter”.

It had long slender limbs held in an upright posture, suggesting it was a swift and agile runner capable of chasing after fast-moving prey. Since it lived in a semi-arid environment that seems to have been a major nesting site for the herbivorous Convolosaurus, their hatchlings probably also made up a large part of its diet during the breeding season.

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[jolikmc]

*metallic boop sound* by Neosuchia on DeviantArt

[astronomy-to-zoology]

Sotmatosuchis inermis

...was a very large (10m/32ft) stomatosuchid crocodilian from the late Cretaceous of Egypt. Unlike many other crocodyliforms it is largely unknown what exactly S. inermis ate. Its flattened skull had a long, lid-like snout which was filled with small conical teeth. Some theorize that the mandible might of been toothless and supported a pelican-like throat pouch. 

Sadly the only known specimen (a large skull, collected by German paleontologist Ernst Stromer) was destroyed when the Munich Museum was bombed in 1944.

Classification

Animalia-Chordata-Reptilia-Crocodylomorpha-Neosuchia-Stomatosuchidae-Sotmatosuchis-S. inermis

Image: Dmitry Bogdanov

[arminreindl]

Croc Paleontology Recap January 2025

The year has just begun and already we got a bunch of pretty neat new studies on fossil pseudosuchians so I'll just briefly go over them and unless I forget or end up procrastinating/getting too busy I'll hopefully be able to keep this going throughout the rest of the year.

Just to give you a brief overview, the highlights of this month include: salt glands in gavialoids, crocodilian predation on azhdarchids, diversifications and extinctions in thalattosuchians and a new species of aetoaur from India. Lets begin.

Evidence for salt glands in gavialoids

Starting off with something relating to the dispersal of gavialoids, we got "Evaluation of the endocranial anatomy of the early Paleogene north African gavialoid crocodylian Argochampsa krebsi and evolutionary implications for adaptation to salinity tolerance in marine crocodyliforms" by Pliggersdorfer, Burke and Mannion.

The title already gives a lot away, but the point was that Argochampsa, from the early Paleocene Ouled Abdoun Basin in Morocco, was examined for evidence of salt tolerance. Why? Because the dispersal of gavialoids remains weird. Both modern forms aren't especially keen on saltwater and are only known to consistently occur in freshwater (tho we have a recent example of an indian gharial caught in a fishing net off the coast of India), yet we have plenty of extinct gavialoids that either indicate that the group must have crossed oceans (see any "gryposuchine") or straight up lived at sea (also see some "gryposuchines").

Now, one such example might also be Argochampsa. Both because the Ouled Abdoul Basin famously preserves coastal deposits and because, at least following some phylogenies, Argochampsa might be closely related to the gharials of South America and today (others say its not even a gavialoid but lets ignore that for now). So all things considered one might expect marine habits from Argochampsa, yet so far no such adaptations could be identified. Well, Pliggersdorfer and co. analyzed a thus-far undescribed skull and actually managed to find something. Small depressions on the inside of the skull are suspiciously similar to ones seen in the extinct, fully marine metriorhynchoids, depressions that in the latter have been interpreted as having been left by salt glands. There is also some further evidence through the morphology of the inner ear.

This conclusion further extends to a handfull of other taxa, including the dyrosaurid Rhabdognathus and the recently named gavialoid Sutekhsuchus, and lends itself to the hypothesis that salt glands may have been ancestral to gavialoids, something I personally find unsurprising given their proximity to crocodyloids and their dispersal across the world (really if anything alligatoroids seem like the odd one out).

Fun fact, yours truly is featured in the paper in the form of two silhouettes.

Left: Argochampsa, illustrated by Seismic Shrimp/JW Right: Piscogavialis, perhaps the most famous marine gavialoid, illustrated by Joschua Knüppe

The brain of Paralligator

Second on our neat little list, the neuroanatomy of Paralligator, studied through CT scans and 3D modeling and published on in "Neurocranial anatomy of Paralligator (Neosuchia: Paralligatoridae) from the Upper Cretaceous of Mongolia". Given that I am not great with brain things, I'll keep this one short.

Now for those unfamiliar, Paralligator is part of a somewhat strange clade known as the Paralligatoridae, which contrary to their name are nowhere near real alligators (tho some do look deceptively similar). Instead, they are much more basal members of Eusuchia.

Measurements of the olfactory bulbs, responsible for the sense of smell, indicate that in Paralligator this sense was similarily developed to allodaposuchids and crocodilians, as is the inner ear who's anatomy suggests a semi-aquatic lifestyle. Paralligator does however differ in possessing a mesothemoid, a bony septum in the olfactory region that is also seen in dyrosaurids, baurusuchids and dinosaurs, but not modern crocodiles.

Borealosuchus remains from Colorado

Tho seemingly unexciting, this study, "First record of Borealosuchus sternbergii from thelower Paleocene Denver Formation (lower Danian),Colorado (Denver Basin)" actually helps us fill a neat little gap in our previous knowledge on croc survival across the Cretaceous-Paleocene extinction.

Simply put, though America's croc record across the KPG is rather remarkable, showing both many survivors and some incredible diversification after the impact, Colorado is kind of a blind spot, despite its potential importance. Perhaps one of the best examples of a survivor concerns the genus Borealosuchus, which is both geographically and stratigraphically widespread. To put things into perspective, this genus occured as far north as Canada and as far south as Texas, first appearing in the Late Cretaceous and dying out in the Eocene.

This paper now described several skulls from the Corall Bluff's locality of the Denver Formation, earliest Paleocene, that can be attributed to Borealosuchus sternbergii, definitively extending its range beyond KPG (granted, there are tentatively referred Paleocene occurences elsewhere), making it one of the largest suvivors of the mass extinction, with adults growing up to 2.3 meter in length. The specimens from Colorado are smaller, in the 1.5 to 1.7 meter range, but they are also regarded as immature individuals and are therefore also regarded as usefull in illustrating how the animals changed as they grew into adulthood.

This paper is especially well timed for those that follow @knuppitalism-with-ue 's Formation Stream series. As you might know, Corall Bluffs is to be drawn barely a week from now and this is a fantastic addition.

Left: Borealosuchus drawn by Atak_Draws Right: Distribution of Borealosuchus by Lessner, Petermann and Lyson 2025

Growth of a peirosaur

Our next paper for discussion is "Life history and growth dynamics of a peirosaurid crocodylomorph (Mesoeucrocodylia; Notosuchia) from the Late Cretaceous of Argentina inferred from its bone histology" by Tamara G. Navarro and colleagues. This study conducted the first histology of peirosaurid limb bones, specifically of an indetermined taxon clading together with Uberabasuchus.

As a brief refresher, peirosaurids are a branch of medium to large sized Notosuchians that I personally think can be aptly described as appearing somewhat like scaly dogs or pigs with often robust, wedge-shaped heads and heavily armored bodies.

The results show that the animal had reached sexual maturity, yet was not yet fully grown. What's also noted is the exact growth dynamics of this animal. This is to say, the studied peirosaurid had overall slow growth with cycles of no growth whatsoever and two periods of increased growth, tho once put against other notosuchians the study deems the growth rates to be better described as "moderate". Pepesuchus meanwhile, belonging to the closely related itasuchids, was a fast grower. Extending things beyond their shared clade shows a virtual mish-mash of dynamics, with Araripesuchus buitreraensis displaying slow growth rates (yet Araripesuchus wegeneri having faster rates than the peirosaur), Iberosuchus showing slow rates, and Notosuchus displaying high growth rates (hell, theres even variation between individuals). A final point concerns the age of the individual, which is....contradictory. Based on the limb bones, the study estimates that the animal was at the very least 15 years old, but previous study of the osteoderms has yielded an estimated age of 18 years old. Ultimately, further study is needed, but it does clearly show how the histology of different parts of the skeleton varies.

Shown below, Uberabasuchus terrificus by Scott Reid

Predation on pterosaurs

Here's a fun one, "A juvenile pterosaur vertebra with putative crocodilian bite from the Campanian of Alberta, Canada", once again with a name that tells you very much what you're in for.

Brown and colleagues report on the discovery of a juvenile specimen of the azhdarchid Cryodrakon from the Dinosaur Park Formation of Alberta, Canada. The neck vertebra bears some conical bite marks, notably different from those of theropods, which generally have D-shaped or compressed tooth crosssections (sans spinosaurids, which aren't present). Champsosaurus is also ruled out due to its inferred feeding preferences, weak bite force and slender teeth. Mammals are potential candidates, but the team regards it as more likely that the trace maker was a crocodilian. Considering the fauna of the Dinosaur Park Formation, this would suggest the culprit was either Leidyosuchus, Albertochampsa or an animal described as "Stangerochampsa-like".

Now this is a very interesting, if not exactly unexpected interaction. On the one hand, having direct fossil evidence for this is a big deal, even if we don't know if the bite marks were left due to the pterosaur being actively hunted or if they were simply left when a lucky croc came across the carcass of an already deceased Cryodrakon. On the other hand, crocodiles and kin are notoriously opportunistic and broad in their diet, so one feeding on a pterosaur is something that seems like a no-brainer in principle, especially a relatively small individual with a wingspan of "only" 2 meters. This is further supported by the fact that crocodilian bite marks have also been reported from the Romanian pterosaur Eurazhdarcho.

Obvious difference in prey size and geography aside (and taxon names even within the chosen setting while we're on it), Prehistoric Planet really nailed the nailon the head with this one.

In the left corner, a juvenile Cryodrakton (art by Hank Sharpe). In the right corner, Leidyosuchus (art by Gunnar Bivens) LET THEM FIGHT (or scavenge)

Evolutionary trends and extinctions in Thalattosuchia

This one's a last minute entry, by which I mean this one got just published as I was about to wrap this whole thing up. "Analysing Thalattosuchia palaeobiodiversity through the prism of phylogenetic comparative methods" explores how the evolution and the extinctions of members of this group were shaped by both biotic and abiotic factors.

Given the shere breadth of this topic, a quick summary of thalattosuchia seems kinda in order. In short, thalattosuchians are a group of what are likely to be early crocodyliforms adapted to life at sea. They can be split into two groups, the teleosauroids, superficially gharial like animals that likely stuck to coastal waters, and the metriorhynchoids, open ocean animals with fluked tails, no body armor and paddle-like limbs. Both groups reached their greatest diversity in the late Jurassic, but managed to survive into the Cretaceous before disappearing entirely.

The study recaps that thalattosuchians first reach great diversity during the Toarcian, tho this is likely influenced by preservation bias thanks to Lagerstätten such as the Posidonia shale, and a later diversification takes place during the Bathonian. Regardless, the transition from the lower to middle Jurassic sees an increased trend in both thalattosuchian groups towards shorter snouts, which are associated with durophagy or hypercarnivory. This essentially gives rise to the teleosauroids of the Machimosaurinaei, which appear during the Bathonian and have blunt, robust teeth, as well as the metriorhynchoid Geosaurinae, which appeared at the same time and had ziphodont (serrated teeth). The reasons for this could be twofold. On the one hand, thalattosuchians were very abundant, so expanding into new nisches helped them coexist, with ecosystems preserving fish-eaters, hypercarnivores, durophages and more at the same time. More of an underlying factor could be a drop in ichthyosaur diversity, leaving plenty of open nisches for these crocs to fill.

Subsequently, during the transition from the Middle to Late Jurassic, there was another diversification event with both groups establishing new major clades, possibly associated with the warm temperatures of the Late Jurassic, before the diversity crashes with the onset of the Cretaceous. The authors note that this too might have been related to climate, with the Cretaceous survivors mostly being found in warmer waters.

Left: A Dakosaurus ambushing an ichthyosaur by Gabriel Ugueto Right: A large Machimosaurus rests on the beach as a sauropod approaches, art by Joschua Knüppe

and for the final study I wanna talk about

Kuttysuchus: A new Aetosaur from India

Now, by all accounts one might be surprised to see this just kinda thrown in at the end here rather than getting a dedicated post as I usually like to do with new forms. And truth be told, theres just not that much to say about "A New paratypothoracin aetosaur (Archosauria: Pseudosuchia) from the Upper Triassic Dharmaram Formation of India and its biostratigraphic implications".

Kuttysuchus is our first pseudosuchian to be described this year and to get things out of the way, its not super exciting in terms of material. Like some other recently named aetosaurs, Kuttysuchus is based entirely on a handfull of osteoderms. And there's nothing wrong with that, after all osteoderms are rather distinctive for these animals. It does however mean that the information we can get from them is a bit limited and thus makes it hard to really put together something engaging.

More interesting than the anatomy then is the range and its relationship to other aetosaurs. The fossils are known from the Dharmaram Formation of India, which you might recall is also home to the recently named Venkatasuchus. Both Venkatasuchus and Kuttysuchus are members of the Paratypothoracini, tho the former is significantly more derived and the latter more basal.

Fossil osteoderms of Kuttysuchus, all belonging to the central double row that stretches across the back.

I'll be entirely honest. This was a lot more work to type out than anticipated, but admittedly also fairly rewarding. Hopefully you dear reader found it equally interesting, and hey, congrats on making it to the end.

[kiragecko]

[Image shows a small crocodilian with the text,

MHNM-kh01 Sidi Chenane Morocco Danian (Paleocene) Neosuchia Tethysuchia Pholidosauridae Osteoderms not included Scale: 20 cm

and a small map showing it's location in North-Central Morocco.

A silhouette of Steve Irwin crouching with arms outstretched (probably to excitedly tell us 'I'n't she a beauty?') is in the background for scale.

The pholidosaurid is about the length of Steve's outstretched arms.

End ID.]

Something that few people are aware of, but pholidosaurids managed to live for much longer than most know. Although its true that this group peaked around halfway through the Cretaceous (with Sarcosuchus), a paper from 2020 not only extends the record to the Maastrichtian, but also showcases material from Morocco dated to the early Paleocene But unlike the other three groups, pholidosaurids seem to have gone extinct soon afterwards. That is, unless fossils are found that extend their range yet again.

[confusedhadrosaur]

Day 17: Shamosuchus djadochtaensis (may bite when hugged)

[alphynix]

Stomatosuchus inermis, a huge crocodylomorph from the Late Cretaceous of Egypt, living about 100-94 million years ago. Estimated to have been up to 10m long (~32′10″), it had an unusually long and flat head, with the upper jaw lined with hundreds of tiny conical teeth. Exactly what it ate with such a strange mouth is unknown, but the shape of its lower jaw suggests it may have had a large throat pouch -- perhaps filter-feeding somewhat like modern baleen whales.

Only one fossil has ever been found, a single large skull which was kept in the Munich Museum. Unfortunately, in 1944 the museum was severely damaged in an Allied bombing raid, and Stomatosuchus was among the specimens destroyed -- along with the original material of the much more famous Spinosaurus.