#paralligator

[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.

[skyradiant]

Life of our Prehistoric Planet: Shamosuchus djadochtaensis.

[saritapaleo]

Originally known only from a foot, with scarce remains found since, Elmisaurus rarus means “Rare Foot Sole Lizard.” Even today, Elmisaurus fossils are highly fragmentary, as are most Caenagnathid remains, and consist mostly of foot and hand bones. However, if the fossils of Nomingia gobiensis can actually be attributed to Elmisaurus, which they may be, we might have a bigger picture of the animal. Elmisaurus has been the subject of but one study so far, where 23 foot bones from various specimens were studied for signs of stress fracture, and none were found. This animal was probably lightly built and not using its feet for strenuous activities. Rather, like other oviraptorosaurs, it would have relied on a sharp beak and strong bite force, lending to either herbivory of tough plant material or omnivory of both plants and small creatures.

Found in Late Cretaceous Mongolia, Elmisaurus rarus would have lived in the arid canyons of the Nemegt Formation. This environment was not entirely desert like the older Barun Goyot and Djadochta Formations, but also filled with thickly wooded forests of tall conifer trees and shallow lakes. It would have shared this environment with other oviraptorosaurs like Rinchenia, Nemegtomaia, and Avimimus. It would have also lived alongside troodontids like Tochisaurus and would have had to look out for Tyrannosaurs like Bagaraatan and Tarbosaurus. Hadrosaurs like Barsboldia and Saurolophus, the pachycephalosaurs Homalocephale and Prenocephale, sauropods like Nemegtosaurus, and the crocodylomorph Paralligator also lived here, as well as turtles, frogs, and small mammals.

If Nomingia is actually Elmisaurus, then it would have also lived alongside ornithomimosaurs like Anserimimus, Gallimimus, and Deinocheirus, the dromaeosaur Adasaurus, the bird Brodavis, alvarezsaurs like Mononykus, troodontids like Zanabazar, and Therizinosaurus in the Bügiin Tsav locality of the Nemegt Formation.

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!

[saritapaleo]

The gracile caenagnathids are notorious for fossilizing badly, and as such Nomingia gobiensis is only known from its spine, upper legs, and tail (which is honestly more than most other caenagnathids). However, its tail represents a significant discovery for oviraptorosaurs. Nomingia had five fused vertebrae at the tip of its tail, a structure similar to the pygostyle of birds, that would have supported a fan of tail feathers. When Nomingia was found in 1994 and described in 2000, this feature was thought to be unique to birds. And while we have evidence of tail fans in other oviraptorosaurs, pygostyles themselves are rare. It’s unknown why Nomingia would have needed this, as it was certainly too big for flying. Perhaps, like Khaan’s tail fan, it was used for display, and the structure would have allowed it to have a sturdier, larger, more “sexy” tail fan.

As of 2021, it has been suggested that Nomingia may actually be Elmisaurus, but further study is needed to confirm this. Since caenagnathid fossils tend to be so fragmentary, this may take some time.

Hailing from the Bügiin Tsav and Nemegt localities of Mongolia’s Late Cretaceous Nemegt Formation, Nomingia would have lived alongside Avimimus nemegtensis in this seasonally arid environment characterized by cliffs, shallow lakes, and patches of conifer forests. If not Elmisaurus itself, it would have lived alongside it as well as the oviraptorids Nemegtomaia in the Nemegt and Oksoso in the Bügiin Tsav. There were of course other dinosaurs here, including Therizinosaurus, the troodontid Tochisaurus, the tyrannosaur Bagaraatan, the sauropod Nemegtosaurus, the hadrosaur Barsboldia, and the pachycephalosaur Homalocephale in the Nemegt.

In the Bügiin Tsav, Nomingia would have lived alongside the troodontid Zanabazar, the dromaeosaur Adasaurus, the bird Brodavis, the ornithomimosaurs Anserimimus and Deinocheirus, and the alvarezsaur Mononykus.

It would have come across Gallimimus, the hadrosaur Saurolophus, the pachycephalosaur Prenocephale, and the tyrannosaur Tarbosaurus in both localities. Crocodylomorphs like Paralligator, fish like Harenaichthys, and turtles could be found in the freshwater lakes.

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!