#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.

[confusedhadrosaur]

Day 24: Burkesuchus mallingrandensis

[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

[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

[confusedhadrosaur]

Day 17: Shamosuchus djadochtaensis (may bite when hugged)

[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.

[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.