The dawn of dinosaurs

SATURDAY, 29 JANUARY 2011

A new dinosaur has been discovered in Argentina ^[1]. Eodromaeus, the “dawn runner,” lived around 230 million years ago. This makes it the earliest known carnivore in the long line that culminated in the mighty Tyrannosaurus and would eventually give rise to modern birds. It is also believed to be only a few million years removed from the common ancestor to all dinosaurs.

Fossils of Eodromaeus were found in the Valley of the Moon, beneath the Andes, in 1996. Over the last 50 years this has been a highly productive site for palaeontologists, with dinosaur remains spanning over 5 million years.

Eodromaeus would have lived alongside Eoraptor “dawn plunderer”, which, in light of Eodromaeus, has been redesignated as one of the first herbivorous dinosaurs, an ancestor of the sauropods. Both species, as with most early dinosaurs, were exceptionally small and agile. Eodromaeus is estimated to have been about 1.2 metres long, weighing up to 15lbs.

Eoraptor has spent the last 20 years misrepresented as a carnivore, and Eodromaeus was originally thought to be another Eoraptor as both have very similar body shapes and sizes. At such an early stage in evolution, only careful examination of the skulls and teeth from both species was able to differentiate the herbivore from the carnivore.

It remains a great mystery how such pipsqueaks came to dominate the world for over 100 million years, a mystery that, palaeontologists hope, may soon be unlocked in the Valley of the Moon. Findings so far suggest that dinosaurs took power slowly. 230 million years ago, only 10% of reptiles were dinosaurs and none of these were particularly big or powerful. A mass extinction which occurred 200 million years ago may have been pivotal in the rise to royalty.

Written by Jonathan Lawson

References:

Ricardo N. Martinez et al., “A Basal Dinosaur from the Dawn of the Dinosaur Era in Southwestern Pangaea,” Science 331, no. 6014 (January 14, 2011): 206 -210