Unaysaurus

Chapter • Meet the dinosaur

Overview

Unaysaurus tolentinoi was a small, slender plant-eating dinosaur from the Late Triassic of southern Brazil. It measured only about 2.5–3 metres from snout to tail tip and probably weighed around 70 kilograms – roughly the mass of a large goat, but with a far longer neck and tail. The skull was low and elongated, about 24 centimetres long, and carried small leaf-shaped teeth with coarsely serrated edges, well suited to snipping soft plant tissue. The neck was fairly long, the hind limbs sturdy, and the arms noticeably shorter, ending in grasping hands with an enlarged thumb claw. Unlike the giant sauropods that later grew from the same branch of the family tree, Unaysaurus walked on two legs. The proportions of its limbs indicate a habitually bipedal animal that held its body horizontally, balancing on its hind legs with the tail carried clear of the ground rather than dragging behind it. The hands were probably more useful for pulling down branches and foliage than for bearing weight. No feathers or feather-like structures are known in this group; the skin was almost certainly covered in small, irregular scales. Because only a single individual has been found, we know very little about its social life, growth rate, or maximum age. Unaysaurus was a herbivore that most likely browsed on ferns, horsetails, conifer shoots and other low vegetation, reaching from ground level up to a couple of metres when it stretched its neck. Its spatulate, serrated teeth could not grind food, so the plant matter must have been broken down by bacterial fermentation in a capacious gut. Some researchers argue that the very earliest sauropodomorphs may have been partly omnivorous, but the dentition of Unaysaurus points firmly towards a plant-based diet. The fossil was found in 1998 by Tolentino Marafiga near São Martinho da Serra in the state of Rio Grande do Sul, in rocks of the Caturrita Formation. The species was described in 2004 by Luciano Leal, Sergio Azevedo, Alexander Kellner and Átila da Rosa. The genus name derives from "unay" ("black water") in the Tupi language, after the locality of Água Negra, while the species name honours its discoverer. The holotype, UFSM 11069, includes an almost complete skull with lower jaw plus parts of the vertebral column, pelvis and hind limbs, making it one of the most complete early sauropodomorphs from Triassic South America. Its close relationship to the European Plateosaurus supports the picture of a connected Pangaea across which animals could disperse.

Chapter • Where it lived

Habitat

Unaysaurus lived about 227–225 million years ago, during the Norian stage of the Late Triassic, in what is now southern Brazil. The fossil comes from the Caturrita Formation of the Santa Maria Basin, near São Martinho da Serra in Rio Grande do Sul. The landscape was one of river floodplains and sandy channels in a continental interior with pronounced dry seasons, dotted with conifers, ferns and horsetails along the watercourses. Its neighbours included other early bipedal dinosaurs, fox-sized cynodonts, dicynodonts and small reptiles – a fauna from the very time dinosaurs were beginning to take over.

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy