Tawa

Chapter • Meet the dinosaur

Overview

Tawa hallae was a small, lightly built and strictly two-legged predatory dinosaur from the Late Triassic. It measured roughly 1.8–2.5 metres from snout to tail tip, with much of that length taken up by a long, stiffened tail that balanced the body over the hips. It stood about 60–70 centimetres tall at the hip and weighed only some 10–20 kilograms. The skull was low and narrow and lined with numerous small, recurved and serrated teeth; the neck was long and S-curved, and the body was carried horizontally, with the tail held clear of the ground. The arms were short but muscular and tipped with sharp claws, while the long, slender hind limbs mark Tawa as a fast and agile runner. No feather impressions are preserved for Tawa, which is unsurprising given that the bones come from coarse river deposits where soft tissue rarely survives. Because simple filamentous feathers are known from many later theropods, artists often give Tawa a light covering of fuzz along the neck and back, but this remains a hypothesis rather than a fact. The neck and trunk vertebrae of Tawa contain air-filled cavities — pneumatic invaginations showing that the animal already possessed a bird-like system of air sacs connected to the lungs. This is one of the oldest clear examples of that respiratory architecture in dinosaurs and supports the idea that efficient avian-style breathing evolved very early in theropod history. Combined with a lightweight skeleton and long legs, it points to an active animal with a high metabolic rate. Tawa was a meat-eater. Its teeth are classic predator teeth — thin, curved and finely serrated along both edges — built to slice flesh rather than crush bone. Its prey probably consisted of small reptiles, early mammal relatives, amphibians and insects, and it may well have scavenged. Larger hunters shared the same landscape, notably crocodile-line archosaurs such as rauisuchians, so Tawa was far from the apex predator of its world. The fossils were collected between 2004 and 2006 at the Hayden Quarry at Ghost Ranch in northern New Mexico, USA, in the Chinle Formation, and the species was described in 2009 by Sterling Nesbitt and colleagues. The genus name honours Tawa, the sun god of the Puebloan Hopi people of the American Southwest, while the species name commemorates Ruth Hall, founder of the palaeontology museum at Ghost Ranch. The find mattered immediately: the material includes several individuals of different ages and one nearly complete skeleton, and analyses of Tawa helped untangle the early theropod family tree while supporting the idea that dinosaurs originated in what is now South America and spread northwards from there.

Chapter • Where it lived

Habitat

Tawa lived during the Norian stage of the Late Triassic, roughly 215–212 million years ago, in what is now northern New Mexico, USA. Every known specimen comes from the Hayden Quarry in the Petrified Forest Member of the Chinle Formation at Ghost Ranch. At that time the region lay close to the equator on the supercontinent Pangaea and experienced a strongly seasonal monsoon climate with heavy rains alternating with long dry spells. The landscape was one of broad floodplains crossed by meandering rivers, with sandbars, temporary lakes and groves of conifers, ferns and tree ferns. Tawa shared this world with early sauropodomorphs, its close relative Chindesaurus, phytosaurs, aetosaurs and large rauisuchians.

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy