#palaeblr

Once again I'm here to recap exciting fossil croc news. To give a quick rundown of papers from the last week, we had one on non-semi aquatic adaptations in crocodylomorphs (mostly life on land but also notes of marine groups), a paper that I'm biased toward because it feaures two of my silhouettes in its phylogeny.

The two silhouettes of mine used in the study. Duerosuchus representing the Planocraniidae and Trilophosuchus representing Atoposaurids (eventhough it's not one, it was picked since it at least conveys the right proportions).

Thalattosuchians recieved a lot of attention this past week. For starters, in addition to being brought up in the afforementioned paper, they were given a lot more focus in a study comparing the function and phylogenetic importance of their shoulder girdles (and those of dyrosaurids), a metriorhynchoid skeleton of uncertain affinities from the Cretaceous northeast Italy was described and just today we got a study on the braincase anatomy of Thalattosuchus.

The one paper that excited me the most however was the description of ziphodont crocodilian teeth from the Pliocene Otibanda Formation of Papua New Guinea. To those unaware, ziphodont teeth are essentially teeth that are flattened like a blade and bear serrations along their cutting edge, something seen in dinosaurs, monitor lizards and a select few crocodile groups like sebecid notosuchians, planocraniids and some mekosuchines. Now these teeth are nothing new, they've been known since 1967, hell I even mentioned them on both the wikipedia pages for Mekosuchinae and Quinkana, but they were never properly described...until now.

Leave it to Jorgo Ristevski, Ralph Molnar and Adam Yates to tackle this one, describing not just the ziphodont teeth but also the postcranial material and conical teeth from the formation. Now don't expect any new species or genera. Though valuable, the study doesn't cause any major stirr ups. The ziphodont teeth are tentatively referred to the Mekosuchinae, though they are not morphologically distinguishable from other ziphodont groups like sebecids or the previously mentioned planocraniids, mekosuchines are the only ones that fit the time and location. The other fossils are even more ambiguous, the postcrania referred to Crocodylia incerta sedis and the conical teeth to cf. Crocodylus sp., so basically an unknown crocodilian and a modern croc. This at least suggests that two different crocodiles inhabited Papua New Guinea at the time, maybe even three assuming that the postcrania don't belong to either the ziphodont or conical form.

Since New Guinea and Australia were once connected, forming the continent of Sahul, some Quinkana-like mekosuchines could have easily traveled to the island.

The final thing I want to mention is not an actual study, but still newsworthy. Scientists in Peru just revealed whats thought to be the first juvenile Piscogavialis. An amazingly preserved skeleton was unveiled, preserving much of the skull minus the tip of the snout, most of the spinal collumn until the base of the tail, both hindlimbs and some other bones as well (from the photos theres a few ribs at least).

Whats fun is that though described as a juvenile, the animal is estimated to have already reached around 3 meters in length. To put this into perspective, thats the size of the average female saltwater crocodile and just shy of the 4.3 meters reached by the contemporary Sacacosuchus. Now on the one hand, I think calling that a juvenile might be a bit of an exaggeration (then again the term subadult is arguably vague and meaningless) and I'm curious to see whether or not an eventual study will back this up with anatomical features or if its even possible that it could just be an instance of dimorphism between sexes. But thats just me musing on the basis of a few photos.

Anyways, given that they just state that this 3 meter animal is a "juvenile", you might wonder how large the adult would be?

The short answer...large. Yeah Piscogavialis got big. The skull alone measures over a meter in length and a recent paper on Sacacosuchus said that they grow to nearly twice the length of their smaller contemporary. With Sacaco sitting at 4.3 meters, one could easily imagine Piscogavialis reaching 7 to maybe 8 meters (I should make a proper scaling at some point). Here's how Gabriel Ugueto and artbyjrc scaled this animal and yeah, even if it ate fish it could probably do some real damage if provoked.

Yep, it sounds like you’ve got the general idea!

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

It's June 17th, world crocodile day, a day to appreciate these amazing yet endangered animals. They are my personal favourite group of animals period and just endlessly fascinating to me, both those we have today and those that lived in the ancient past. Tho I'm no professional by any means, I strive to learn about them and spread this knowledge. So here's some photos, art and skeletals of fossil crocs (using the term rather liberally I know). Feel free to drop your favourites in the reblogs, doesn't matter if extinct or not.

My newest size comparisson featuring the newly named genus Sutekhsuchus, previously known as Tomistoma dowsoni.

This gharial lived some 17 million years ago in what is now Egypt and Libya, at the time lush coastal environments comprised of swamps, estuaries, lagoons and meandering rivers.

For starters, the rostral boss is a large bump that is located on the snout of some crocodiles just before the eyes, covering the back of the nasal bone and areas of the prefrontals, lacrimals and parts of the frontal bone. This boss, among modern crocs, is most prominent in the American Crocodile. Sidenote, I know its a pain, but here American Crocodile (capitalized C) means Crocodylus acutus. When meaning the crocodiles of America, I'll use Neotropic crocodiles. Also tho I'm usually liberal with the term, here crocodile specifically refers to the genus Crocodylus. Good? Good. Anyhow, this kinda gives them a look thats been likened to the Triassic phytosaurs and makes individuals with said bump really distinct. Below are some pictures which show different indivudals with less and more pronounced bosses.

Now this feature is not unique to American Crocodiles (again meaning C. acutus, I know the terminology is confusing), but can be seen in at least some other neotropic Crocodylus species. Now I've yet to see images of either Morelet's or Orinoco Crocodiles with the same and they don't appear to have been recognized with them by older literature, but there are some Cuban Crocodile skulls also showing a slight boss. If you look at the two photos below, you can see an American Crocodile skull on the left and several skulls of Cuban Crocodiles on the right (from the Quaternary Sawmill Sink on the Bahamas). It's comparably subtle in the Cubans, but there is a boss present in these skulls.

The fun part is that this isn't just a random trait that these crocodiles got out of nowhere. No, the rostral boss is actually a trait thats likely to be ancestral to ALL Crocodylus species of the Neotropics (so again, Morelet's, Cubans, Orinocos and Americans). The oldest known Crocodylus species from the Americas is Crocodylus falconensis from the Pliocene of Venezuela. And guess what, it had that very same bump on its face.

But that's not where the trail ends. No. Back in the 1940s a crocodile was found in Miocene sediments of Northern Africa that had a similar bump. Meaning on the other side of the Atlantic. This was largely ignored at the time, despite the similarities to American and Cuban Crocodiles and their rostral bosses being known back then. But more recently, scientists have taken a second look at this species, Crocodylus checchiai, and concluded that it is a likely ancestor to today's Neotropic crocodiles.