Prestosuchus and the Rauisuchians: The Pangean top predators

File:Prestosuchus-chiniquensis (2).jpg - Wikimedia Commons
An artists impression of Prestosuchus chiniquensis. AKA “Prestes Crocodile”
Image Credit: Dmitry Bogdanov, https://commons.wikimedia.org/wiki/File:Prestosuchus-chiniquensis_(2).jpg

The Mesozoic era is usually associated with one group of animals. You may have heard of them already, but if you haven’t, I’ll give you a clue; the name starts with D! However, during the first third of the Mesozoic era, a time known as the Triassic period, that famous group were only just beginning to establish themselves and radiate into their early sub groups. During this time the Triassic was instead dominated by other animal groups. These included Dicynodonts; large reptilian pig-looking herbivores who were part of a larger group known as “stem-mammals” (the lineage that would give rise to true mammals) and Cynodonts; small omnivorous stem mammals that often lived in burrows. However the animal I will be talking about here belonged to an altogether different reptile group. This animal is Prestosuchus; a huge four legged carnivore that belonged to a line of reptiles known as the Pseudosuchians (the same group that modern crocodiles would descend from). Despite being part of the same lineage, and possessing similar morphological features, Prestosuchus wasn’t a crocodile. Instead it belonged to the now extinct sister group known as the Rauisuchians. This important group of carnivores I think don’t get the attention they deserve, something that I shall now try rectify!

The first fossils of Prestosuchus (from a species eventually named Prestosuchus chiniquensis) were discovered in Brazil during the war torn year of 1942 by a German Palaeontologist named Friedrich von Huene. However, while he is credited as the discoverer of the fossil he was only able to do it with the help of his colleague; Vicentino Prestes de Almeida. A local self-taught Brazilian palaeontologist Vicentino is who Prestosuchus is named after, (the name translates to “Prestes Crocodile”), while the “chiniquensis” part refers to Vicentino’s birthplace of Chiniquá in Brazil. The two men found these first fossils in a rock formation known as the “Santa Maria formation”. Back when Prestosuchus was alive, Santa Maria was the site of a vast watering hole where animals of all kinds would gather to take a much needed drink. For a predator like Prestosuchus this provided regular hunting opportunities and one could imagine that the area around this watering hole was Prestosuchus’ home, with little need to move far from such fine real estate! (unless it became so hot that the watering hole dried up of course). Since this first discovery, two other Prestosuchus species have been identified; Prestosuchus nyassicus (originally thought to be a different, though closely related, Pseudosuchian named Stagonosuchus nyassicus) and an as yet unnamed species, which sadly will probably not have a naming competition any time soon!

Prestosuchus lived during the early to mid-Triassic period (roughly 241-236 million years ago). During this time all the continents of the world were joined together into one great landmass known as Pangea. Pangea would have been a hot holiday destination, with the dry climate resulting in an arid central region. However towards the coast and away from the equator the climate was a lot milder allowing the growth of wet and dry seasonal forests battered by regular monsoons. It was in these places where Prestosuchus was found and at 6.5 metres long (based on measurements of a specimen discovered in 2010) and a ton in weight it would’ve been hard to miss! As I mentioned earlier, Prestosuchus shares many similarities with its relatives the crocodiles and alligators. These include regular tooth replacement, strong jaws, a thick muscular body and, most notably, a row of hard scaly scutes that ran along its neck, back and down its tail. These hard scutes would’ve given protection from prey violently defending themselves or indeed from other Prestosuchus’ looking to pick a fight. It is also possible (and this is speculation on my part) that like crocodiles these scutes may have had a thermoregulatory function, keeping the carnivore cool by releasing excess heat through them. However these scutes did have one drawback; their weight would have slowed Prestosuchus down, meaning that it probably couldn’t run very fast. However this might not have been that much of a problem for two reasons. Firstly, Prestosuchus is thought to have been an ambush predator. Having targeted its prey using the binocular vision provided by its forward facing eyes (a key predator trait) Prestosuchus would’ve burst out of an ambush site and used its strong jaw muscles (attached at the back of its wide skull) to powerfully crush small animals and inflict massive wounds on any animal large enough to survive the first attack. Secondly the Dicynodonts that were its main food source (e.g. Dinodontosaurus & Stahleckeria) were not very fast themselves. So Prestosuchus could keep up with them just fine. Besides when you have powerful jaws and a heavy body that can overpower anything in your way who needs speed!

File:Prestosuchus skull diagrams.png - Wikimedia Commons
Skull diagrams of Prestosuchus. Note how wide the back of the skull is. This anchored large muscle that gave Prestosuchus its fearsome bite!
Image Credit: Lacerda et. al. 2016, https://peerj.com/articles/1622/

The Rauisuchians were the top predators of the Triassic. They ruled over nearly all the Pangean supercontinent, ranging from only a metre long to the 9 metre long Saurosuchus (who was very closely related to Prestosuchus). Nearly all of them were covered in characteristic heavy scutes and they were nearly all quadrupeds (walked on four legs). However some Rauisuchians did occasionally break the mold, such as the North American Postosuchus; which possessed reduced forelimbs and is thought to have walked on two legs. The Rauisuchians were so successful that the early theropod dinosaurs, which actually co-existed with them, spend the majority of the Triassic in their shadow. However this wasn’t to last. While Prestosuchus itself went extinct around 235 million years ago the Rauisuchians managed to cling on until the end of the Triassic (around 201 million years ago). At this time the world was going through a massive extinction event that was caused by massive volcanic eruptions that split Pangea apart and fuelled a runaway global warming event and acidification of the oceans. This event is so big that it is classed as one of the “big 5” extinction events, alongside the K/T (65 million years ago) and end-Permian (250 million years ago) events to name two. The Rauisuchians were one of many animal groups that didn’t survive the end Triassic, dying out alongside other Triassic defining groups like the Dicynodonts, Rynchosaurs and other Pseudosuchian groups. Why these groups didn’t survive whilst the dinosaurs did is a mystery. Dinosaurs were not a “superior” species as previous narratives have stated. In fact studies (such as one published in 2008 and led by Dr Steve Brusatte) have found that Pseudosuchians contained more species and more variety between species during the Triassic period than the dinosaurs. Furthermore dinosaurs and Pseudosuchians were so similar to each other that even palaeontologists have classified an animal as part of one of these groups only to find out they were the other!. It is a real mystery and the answer may simply be just chance, with dinosaurs only just managing to fare better in the chaos. If the end Triassic extinction event hadn’t happened it’s possible that the Pseudosuchians would’ve been the dominant animals of the entire Mesozoic instead of the dinosaurs, with animals like Prestosuchus being as successful and iconic as theropod dinosaurs like T-Rex and Allosaurus.

So Prestosuchus and the Rauisuchians as a whole are truly fascinating reptiles and I’m happy that I finally got to talk about them in this blog article. I hope that in the future I will be able to introduce you to other fascinating crocodile relatives, as the crocodile family tree, as shown by Prestosuchus, is a truly rich, varied and colourful lineage!

File:Saurosuchus and hyperodapedon.jpg
Rauisuchians were the “top dogs” in Pangea. This piece of paleoart depicts the 9 metre long Saurosuchus, with Hyperodapedon the animals looking to get away from it!
Image Credit: ABelov2014, https://www.deviantart.com/abelov2014/art/Saurosuchus-Hyperodapedon-753703812

References/Further Reading

Desojo et. al. 2020 study on the anatomy, taxonomy and phylogenetic relationships of Prestosuchus chiniquensis

Desojo, Julia Brenda, von Baczko, María Belén, and Rauhut, Oliver W.M. 2020. Anatomy, taxonomy and phylogenetic relationships of Prestosuchus chiniquensis (Archosauria: Pseudosuchia) from the original collection of von Huene, Middle-Late Triassic of southern Brazil. Palaeontologia Electronica, 23(1):a04. https://doi.org/10.26879/1026

• A blog article reporting on the 2010 discovery of a specimen of Prestosuchus. This fossil is important as it showed that Prestosuchus was much larger than previously thought

Mike, “Most Complete Fossil of a Crocodylotarsian found in Brazil”, Everything Dinosaur, www.blog.everythingdinosaur.co.uk, https://blog.everythingdinosaur.co.uk/blog/_archives/2010/05/12/4528166.html

• Another blog article, also from everything dinosaur, that provides more background on Prestosuchus while also previewing a model of it

Mike, “Preparing for Prestosuchus”, Everything Dinosaur, www.blog.everythingdinosaur.co.uk, https://blog.everythingdinosaur.co.uk/blog/_archives/2018/11/07/preparing-for-prestosuchus.html

• “The Rise and Fall of the Dinosaurs” by Steve Brusatte. Chapters 2 and 3 (“Dinosaurs rise up” and “Dinosaurs become dominant”) details what dinosaurs were like in the Late Triassic, the Pseudosuchians that co-existed with them and the end Triassic extinction event.

Brusatte et. al. 2008 paper discussing the evolutionary radiation of dinosaurs and Pseudosuchians

Brusatte, S. L., et al. (2008). “Superiority, Competition, and Opportunism in the Evolutionary Radiation of Dinosaurs.” Science 321(5895): 1485-1488.

Lacerda et. al. paper analysing the 1942 fossils of Prestosuchus chiniquensis

Lacerda MB, Mastrantonio BM, Fortier DC, Schultz CL. 2016. New insights on Prestosuchus chiniquensis Huene, 1942 (Pseudosuchia, Loricata) based on new specimens from the “Tree Sanga” Outcrop, Chiniquá Region, Rio Grande do Sul, Brazil. PeerJ 4:e1622 https://doi.org/10.7717/peerj.1622

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