Sanjuansaurus

Chapter • Meet the dinosaur

Overview

Sanjuansaurus gordilloi was a lightly built predator roughly three to four metres long and probably weighing somewhere between forty and just over a hundred kilograms. It walked on two legs, carried its body horizontally with a long stiffened tail counterbalancing the front half, and held its head at about hip height — nothing dragged along the ground. The forelimbs ended in relatively long grasping hands, and the jaws carried recurved, serrated blade-like teeth. No skin or feather impressions are known for herrerasaurids, so reconstructions normally show scaly skin rather than a feather covering. Sanjuansaurus belongs to Herrerasauridae, a family of very early meat-eating dinosaurs from the Late Triassic. Exactly where herrerasaurids sit in the dinosaur family tree is still argued over: many analyses recover them as the earliest theropods, others as saurischians just outside Theropoda. That uncertainty is part of what makes the animal important, because every additional Triassic skeleton refines our picture of what the first predatory dinosaurs looked like before the group came to dominate terrestrial ecosystems. As a hunter, Sanjuansaurus was probably an agile pursuer of small and medium-sized prey. Rhynchosaurs, early cynodonts and small reptiles are common in the same beds, and the bladed teeth were well suited to slicing flesh while the clawed hands helped hold struggling prey. It shared its world with the larger herrerasaurid Herrerasaurus, the small early dinosaur Eoraptor, and formidable non-dinosaurian predators such as the rauisuchian Saurosuchus. The species was described in 2010 by Oscar Alcober and Ricardo Martínez from a partial skeleton, holotype PVSJ 605, collected in the Ischigualasto Formation of San Juan Province in north-western Argentina. The genus name refers to the province; the species name honours Raúl Gordillo, the museum technician who found and prepared the specimen. The material includes jaw fragments, neck vertebrae, ribs, parts of the pelvis, a scapula and hind-limb bones — enough to show several features of the shoulder blade and vertebrae that separate it from Herrerasaurus.

Chapter • Where it lived

Habitat

Sanjuansaurus lived in the Late Triassic, in the Carnian stage roughly 231 million years ago. Every known fossil comes from the Ischigualasto Formation of the Ischigualasto–Villa Unión Basin in San Juan Province, north-western Argentina. Today the region is desert badlands, but in the Triassic it was a river-crossed floodplain with strongly seasonal rainfall and stands of conifers and ferns. Ash from nearby volcanoes buried carcasses and allows the layers to be dated very precisely by radioisotope methods. The holotype came from the lower part of the formation, in the same levels that yield Herrerasaurus and Eoraptor.

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy