Lectures

Summary from “A Sound of Distant Thunder: How a New Dinosaur from South Africa Sheds Light on the Beginnings of the Giant Sauropod Dinosaurs,” Wed, Nov 18, 2009 - Dr. Matt Bonnan

Sauropod dinosaurs were gigantic, quadrupedal, long-necked herbivores that reached sizes that no other land-living animals have ever matched. Although their anatomy and general relationships are well-documented, the beginnings of their rise to gigantism in the Early Jurassic remain poorly understood. In particular, it has been difficult to tell which features of their skeletal anatomy developed before or after they became giants.

The new Early Jurassic dinosaur from South Africa described in the November 11, 2009 Proceedings of the Royal Society B sheds fresh light on some of these intriguing questions. Thanks to support from National Geographic and Western Illinois University, this new dinosaur, Aardonyx (“Earth claw”), which appears to be closely related to the common ancestor of all sauropods, was discovered in South Africa.

An analysis of the bone microstructure of this 7m (20 feet) long herbivore indicates that it was young and still growing. Its skeletal anatomy shares a number of key features with sauropods. Limb proportions show that Aardonyx was a biped, although its forearm bones interlock (like those of quadrupedal sauropods), suggesting that it could occasionally walk on all-fours. The skull and jaws show signs that this dinosaur had a wide gape and could bulk-browse, an adaptation amplified later in sauropod dinosaurs.

Despite its "small" size, sauropod-like vertebral joints had developed to brace its back bone, and the thigh bone (femur) was straightened for weight-support. The feet were flattened, bore large claws, and were more robust medially, features of a weight-bearing axis shifted towards the midline as in their giant near-descendants.

The body plan of Aardonyx appears to be pre-adapted for gigantism, and, based on its position on the dinosaur family tree, it most likely approximates that of the sauropod common ancestor.

Thus, this 195 million year old South African dinosaur provides significant insight into the later rise and radiation of the sauropod giants.