#late triassic

Newtonsaurus cambrensis, a large basal theropod from the Late Triassic

Phytosaur Smilosuchus gregorii, of Late Triassic, USA!

While the pseudosuchians were still figuring things out in the Triassic, trying out diverse body types, the entirely unrelated phytosaurs had already perfected the semi-aquatic reptilian predator bodyplan. Phytosaurs are known from many different morphologies, specifically with vastly different skull forms, though they can be told apart from pseudosuchians by the position of their nostrils close to their eyes on their snout. One of the largest phytosaurs was the North American Smilosuchus. There are three known species of Smilosuchus, each with different skull morphologies. Smilosuchus gregorii, seen here, had a robust skull, less long and slender than its relatives. Like other phytosaurs, it had heterodont teeth; with large tusks at the front of its mouth for impaling prey, and smaller, blade-like teeth near the back for slicing flesh. It had powerful jaw muscles, and was likely able to hunt large prey, perhaps ambushing the giant dicynodonts and even aetosaurs of the time.

Smilosuchus gregorii was found in the Late Triassic Chinle Formation of Arizona, USA. It would have lived alongside its Smilosuchus relatives, S. adamanensis and S. lithodendrorum, and other phytosaurs like Leptosuchus, Machaeroprosopus, Pravusuchus, and Protome. Pseudosuchians lived here too, though they had the land colonized while the phytosaurs dominated the waters. These included the aetosauriformes Acaenasuchus and Revueltosaurus, the true aetosaurs Adamanasuchus, Calyptosuchus, Desmatosuchus, Kryphioparma, Paratypothorax, Rioarribasuchus, Scutarx, Typothorax, and Tecovasuchus, the small, cat-like Hesperosuchus and Parrishia, the bipedal, theropod-like predator Poposaurus, and the giant land predator Postosuchus. Other archosaurimorphs Smilosuchus would have come across would have been the tanystropheid Akidostropheus, doswelliids like Doswellia and Vancleavea, allokotosaurs like Puercosuchus and Trilophosaurus, and others like Syntomiprosopus. Other animals that lived here (and could have been preyed on by Smilosuchus) included the enigmatic Acallosuchus, drepanosaurs like Ancistronychus, Fabanychus, and Skybalonyx, cynodonts like Kataigidodon, the dicynodont Placerias (thought to be Smilosuchus’ preferred prey), and temnospondyl amphibians like Anaschisma.

(Type femur [thigh bone] of Gondwanax paraisensis, from Müller, 2024)

Meaning of name: Gondwanax = Gondwana king [in Greek]; paraisensis = from Paraíso do Sul

Age: Middle–Late Triassic (Ladinian–Carnian)

Where found: Santa Maria Formation, Rio Grande do Sul, Brazil

How much is known: A right femur (thigh bone), along with several vertebrae and a partial pelvis from the same site. It is unknown whether the other bones belonged to the same individual as the femur.

Notes: Gondwanax was a silesaurid, a group of probably quadrupedal Triassic reptiles that often had adaptations for herbivory (though there is evidence that they also ate insects). Until recently, silesaurids were generally considered to be close relatives of dinosaurs instead of dinosaurs themselves, and I previously excluded them from coverage on this blog. However, multiple recent analyses have suggested that they might in fact be true dinosaurs, specifically early members of Ornithischia ("bird-hipped" dinosaurs), so from here on out I will tentatively include them within this blog's purview. In fact, some of those studies have found that most "silesaurids" may not have formed a unique evolutionary group, but instead a series of lineages with some being more closely related to later ornithischians than others.

Regardless of whether it is a true dinosaur, Gondwanax is one of the oldest known dinosauromorphs (the group containing dinosaurs and their closest relatives). Compared to other dinosauromorphs of similar age, Gondwanax more closely resembles later dinosaurs in having three hip vertebrae (whereas dinosaurs ancestrally appear to have had only two). It is unusual among dinosauromorphs in having a very small fourth trochanter, a attachment point on the femur for muscles that pull the hindlimb backward.

(Schematic skeletal of Gondwanax paraisensis, with preserved bones in orange, from Müller, 2024)

Portrait of dinosauromorph Pisanosaurus mertii from the Late Triassic of Argentina. A partial skeleton of this reptile was discovered in rocks of the Ischigualasto Formation and described in 1967 as belonging to a basal ornithischian. Initially, the animal was even attributed to the Pisanosauridae family. Phylogenetic analyses in 2015 and subsequent years showed it as a relative or even a representative of silesaurids, a group of dinosaurs very close to dinosaurs proper. Pisanosaurus has features of both silesaurids and early ornithischians, which may indicate the relationship of these groups. Judging by the single specimen, it reached a little over a meter in length. The animal's name was given in honor of paleontologist Juan Arnaldo Pisano.

I decided to make a portrait because, due to the uncertain classification, it is not known whether Pisanosaurus was bipedal or quadrupedal. Filamentous structures are speculative.

Welcome back to another day of March Madness. Let's see who made it through to compete today! Our first competitor is the giant ray-finned fish Leedsicthys problematicus! As you can gather from its name, it is is found in Great Britain but has also been found in France, Germany and Chile in early to middle Jurassic-aged rocks.

It is going up against Lisowicia bojani the giant dicynodont. Lisowicia lived in Poland during the Late Triassic. This explains why I find it difficult to say.

Thalassiodracon

Thalassiodracon — вимерлий рід плезіозаврів з родини Pliosauridae, що існував у пізньому тріасі – ранній юрі і відомий виключно з Нижнього Ліасу Англії. Типовий і єдиний вид — Thalassiodracon (Plesiosaurus) hawkinsi (Owen, 1838).

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