Pseudosuchian Saurosuchus galilei, of Late Triassic, Argentina!

This Archovember’s pseudosuchian apex predator is Saurosuchus galilei, a large, heavy Loricatan from Late Triassic South America. Loricata is the clade responsible for many of the most famous large predatory pseudosuchians of the Triassic, including Postosuchus and Prestosuchus, and also includes the crocodylomorphs which would eventually become today’s crocodilians. Saurosuchus was one of the largest high-walking predatory loricatans (often referred to as “rauisuchians”, though this is a paraphyletic term) at 5.5–7 m (18–23 ft) long and weighing over 590 kg (1,300 lb). Studies have shown that it had a mechanically strong skull, but a surprisingly weak bite force for its size, and likely scraped flesh and muscles off of carcasses with its teeth rather than crunched down on bone. Saurosuchus also had large olfactory bulbs but poorly developed optic lobes, indicating it likely relied on a good sense of smell rather than sight to track down prey. It also seemed to have broad hearing sensitivity, especially for low-frequency sounds.

As the apex predator of the Ischigualasto Formation, Saurosuchus galilei had little competition. Its environment was a tropical, fluvial and floodplain ecosystem with strongly seasonal rainfalls, similar to the warm temperate grasslands of Oklahoma and central Argentina. It would have shared the environment (and probably preyed on) other pseudosuchians like the tiny Trialestes, the aetosaur Aetosauroides, and the giant herbivorous shuvosaurid Sillosuchus. Dinosaurs were on the menu as well, including early theropods like Anteavis and Eodromaeus, early sauropodomorphs like Chromogisaurus, Eoraptor, and Panphagia, and of course, the only saurischian that could have possibly given Saurosuchus any trouble, Herrerasaurus. Other reptiles included the bizarre Hyperodapedon, the proterochampsids Proterochampsa and Pseudochampsa, and lepidosaurs like Taytalura. Synapsids lived here as well, including cynodonts like Chiniquodon, Diegocanis, Ecteninion, and Exaeretodon, and dicynodonts like Ischigualastia.

Pseudosuchian Yacarerani boliviensis, of Late Cretaceous, Bolivia!

The notosuchians were a strange group of highly derived and diverse terrestrial pseudosuchians. Where the aetosaurs seemed to be the prototype for ankylosaurs, notosuchians almost seemed to be the prototype for mammals, with their mammal-like teeth and possible fleshy cheeks. They include herbivores (ex. Chimaerasuchus), omnivores (ex. Simosuchus), wolf-like predators (ex. Baurusuchus), and apex predators (ex. Razanandrongobe). They include favorites like the “armadillo croc” (Armadillosuchus), “pug croc” (Simosuchus), “duck croc” (Anatosuchus), and “rat croc” (Araripesuchus rattoides).

One notosuchian that often gets pushed by the wayside is Yacarerani boliviensis. Yacarerani was a small pseudosuchian, with large, protruding teeth. Despite its sinister appearance, Yacarerani appeared to be good parents, as the two known fossils were found together, tending to a nest with eggs. Its heterodont teeth seem to be adapted for grinding or chopping food like tubers and small arthropods, giving it a diet similar to small hogs. It may have lived in small groups, and created burrows to lay eggs in.

The pair of Yacarerani boliviensis and their eggs have thus far been the only fossils found in the Cajones Formation of central Bolivia, but the formation has been correlated with the Adamantina Formation of Brazil, and the Bajo de la Carpa Formation of Argentina, so the paleoenvironment of the Cajones Formation was likely similar. Yacarerani could have lived alongside other notosuchians similar to Barreirosuchus, Baurusuchus, Campinasuchus, Caipirasuchus, Barrosasuchus, Comahuesuchus, Lomasuchus, or Kinesuchus, sauropods like Bonitasaura or Inawentu, unenlagiine theropods like Diuqin, abelisaurid theropods like Viavenator, snakes like Boipeba, iguanian lizards like Brasiliguana, and turtles like Lomalatachelys.

Pseudosuchian Typothorax coccinarum, of Late Triassic, North America!

Our next archosaur, and our first pseudosuchian of this Archovember is Typothorax coccinarum! Pseudosuchians, the lineage that would eventually lead to crocodilians, dominated the Triassic, and did many of the things first that dinosaurs would do later on. Typothorax was an aetosaur, a unique group of pseudosuchians that evolved body armor similar to ankylosaurs. Typothorax was herbivorous, possessing small, leaf-shaped teeth, and had an upturned, shovel-like snout. Their forelimbs also seemed to be uniquely adapted to digging, suggesting they may have found food by rooting around in the soil for roots and tubers.

Typothorax coccinarum is known from the Late Triassic Chinle Formation of Arizona, as well as the Bull Canyon Formation of New Mexico and Texas. In the Chinle Formation, Typothorax would have lived alongside other aetosaurs like Rioarribasuchus and Scutarx, along with smaller pseudosuchians like Hesperosuchus and Revueltosaurus. It would have been preyed on by large rauisuchids like Postosuchus and Vivaron. Other archosaurs Typothorax could have seen in the Chinle Formation would have included lagerpetids like Dromomeron, allokotosaurs like Trilophosaurus, and dosweliids like Vancleavea. Dinosaurs were only just getting a foothold in the Late Triassic, and Typothorax could have come across early saurischians like Chindesaurus and Coelophysis. In the Bull Canyon Formation, the environment was similar, with the addition of the giant, beaked poposauroid Shuvosaurus, as well as the aetosaur Paratypothorax and the phytosaur Machaeroprosopus.

As we know by now, pseudosuchians ruled the earth during the Triassic period, slotting into many different niches and utilizing many different body shapes than just the semi-aquatic crocodilians we have today. Poposauroids especially filled many of the niches dinosaurs would later come to fill, and even resembled them. Our previously visited Lotosaurus was convergent with hadrosaurs and stegosaurs. Poposaurus was convergent with theropod carnivores. The shuvosaurids resembled ornithomimid theropods, and one shuvosaurid in particular: Sillosuchus longicervix, reached sizes that would make the early sauropodomorphs tremble.

Before the dinosaurs ruled the earth, Pseudosuchians laid claim to many of their niches in the Triassic. One of the most diverse clades of pseudosuchians were the Poposauroids, being represented throughout the entire Triassic period in a wide variety of anatomical forms. One such poposaur was the Middle Triassic Lotosaurus adentus of China. This pseudosuchian looked more like a stegosaur or hadrosaur than a crocodile, and behaved similarly, eating plants and living in herds! Lotosaurus would have sheared off leaves with its toothless, beaked jaws, and had a large, barrel-shaped gut to assist in digesting its strange diet, as it likely swallowed plants whole. It had tall neural spines that would have supported a sail or hump and an erect, almost dinosaurian stance.

All known specimens of Lotosaurus have been collected from a bonebed in the Batung (or Badong) Formation. At least 38 individuals of various ages are found in this mass gravesite, but their bones are not scattered, suggesting the herd may have perished due to drought or sickness, their bones later having been covered by sediment and water during the rainy season. It is also possible that Lotosaurus were solitary, and merely gathered around the last small puddle in a dried up pond, before dying of thirst. The bonebed also contains remnants of a temnospondyl and some sort of carnivorous archosauromorph.

We’ve met the largest and oldest notosuchian, Razanandrongobe, already, but the notosuchians were such a widely diverse clade that it would be hard to pinpoint the average notosuchian. They tried all sorts of things, from apex predators to small pug-like herbivores, with a wide variety of body plans. One such notosuchian was Armadillosuchus arrudai, an oddly armadillo-like pseudosuchian from Late Cretaceous Brazil. It was an omnivore, feeding on arthropods, molluscs, roots, and pines and perhaps also scavenging when able. It had well-developed forelimbs that allowed it to dig and possibly even burrow. It was most recognizable, however, for the rigid shield of hexagonal osteoderms just behind the head, followed by a series of mobile bands similar to those of armadillos. This armour was probably embedded beneath the skin in life, allowing for more flexibility.

During the Middle Jurassic of Madagascar the apex predator was not a large theropod, but rather the giant notosuchian Razanandrongobe sakalavae. It is not only the oldest known notosuchian, but also the largest, estimated at 7 metres (23 ft) long. However, it is only known from the tip of its snout, so measurements have to be estimated based on related baurusuchians. Its snout was U-shaped, and taller than it was wide, with forward-facing nostrils. Its teeth were large and serrated on both the front and rear edges, similar to Tyrannosaurus but even larger proportionally. Skull anatomy supports that Razanandrongobe’s diet included hard tissues like bones and tendons, and the serrations on its teeth would have allowed it to crunch into bone. Like the Triassic rauisuchids that came millions of years before, it would have been a large, specialized terrestrial predator.