Camposaurus

Chapter • Meet the dinosaur

Overview

Camposaurus was a small, lightly built predatory dinosaur that ran on two legs across the river plains of Arizona roughly 220 million years ago. It is known only from the lower hind limb – the shin bones, fibulae, the fused ankle bone and the upper ends of the foot bones – but because these elements are so consistent across coelophysids, the animal can be reconstructed as a typical early theropod: about two to three metres from snout to tail tip, with a long neck, a narrow skull, a light body and a very long tail used as a balancing rod. Body mass was probably somewhere between 15 and 35 kilograms, no heavier than a medium-sized dog. There is no fossil evidence of feathers in coelophysids; the oldest confirmed feathers come from later, more bird-like theropods, so Camposaurus is usually restored with scaly or leathery skin – though the question remains genuinely open. The bones say something about how the animal moved. The lower leg is long relative to the thigh, and the foot is narrow and pinched together, a combination typical of fast, enduring runners. Camposaurus held its body horizontally with the tail clear of the ground – no tail-dragging – and probably moved in quick bursts rather than slow patrols. In its close relative Coelophysis the jaws are lined with small, recurved, serrated teeth, and there is no reason to think Camposaurus differed. Its diet almost certainly consisted of small vertebrates: early reptiles, amphibians, small synapsids and perhaps the young of larger species, along with big insects and other arthropods. The Placerias Quarry, where the fossils were found, also yielded the bulky plant-eating dicynodont Placerias, huge phytosaurs and armoured aetosaurs. Camposaurus was no apex predator in that world but a small, agile hunter living in the shadow of far larger crocodile-like archosaurs. The fossils were excavated as early as the 1930s by field parties from the University of California Museum of Paleontology led by Charles L. Camp, at the famous Placerias Quarry near St. Johns, Apache County, Arizona. The material sat in the collections for more than sixty years until Hunt, Lucas, Heckert, Sullivan and Lockley described it as a new species in 1998, naming it Camposaurus arizonensis in Camp's honour. Several researchers questioned whether the remains were distinctive enough to carry a name of their own, but a detailed reassessment by Sterling Nesbitt and Martín Ezcurra in 2015 concluded that the combination of ankle features is unique, making Camposaurus valid – and one of the oldest securely dated neotheropods known anywhere.

Chapter • Where it lived

Habitat

Camposaurus lived in the Late Triassic, during the Norian stage some 221–218 million years ago, in what is now eastern Arizona, USA. The fossils come from the Placerias Quarry near St. Johns in Apache County, in beds assigned to the lower Chinle Group (Bluewater Creek Formation). At that time the region lay close to the equator on the western side of the supercontinent Pangaea, under a hot, strongly seasonal monsoon climate. The landscape was one of broad floodplains crossed by braided rivers, boggy hollows, lakes that shrank away in the dry season, and stands of conifers, ferns and seed ferns. The quarry's bone bed is packed with remains of the dicynodont Placerias, phytosaurs, aetosaurs and early amphibians – an ecosystem in which dinosaurs were still only a minor component of the fauna.

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy