|An artist's impression of Asilisaurus kongwe with |
the sail backed Hypselorhachis in the background
One such creature is Asilisaurus kongwe, which was discovered in 2001 from 240 million year old, mid-triassic rocks on Tanzania, Africa. Unlike many different proto-dinosaurs and late ancestors, fossil remains of this creature were common, with bones from over 14 different individuals recovered from a single bone bed, allowing a skeleton to be constructed, minus parts of the hand and skull. This new creature stood around 1 to 1.5 metres tall at hip height, was around 20 to 30 kilograms and 1 to 3 metres in length.
|A skeletal reconstruction of Asilisaurus kongwe as the fossil of the creature|
It falls just outside of the dinosaur family tree by just 10 million years. What makes this discovery interesting is the way the creature moved. It was a quadruped, walking and running on four legs. The earliest dinosaurs were bipeds, meaning that the change in locomotion occured in a short period of time. While we have fossils of the very last ancestors of the famous reptiles which show signs of being able to move both on four and two legs, the change was actually more complex than one might think.
|The proposed relationship of Asilisaurus to the dinosaurs|
The question is what drove this sudden change in locomotion which would ultimately lead to the evolution of the dinosaurs? 'The research suggests that at least three times in the evolution of dinosaurs and their closest relatives, meat-eating animals evolved into animals with diets that included plants' said Randall Irmis, curator at the Utah Museum of Natural History.
'These shifts all occurred in less than 10 million years, a relatively short time by geological standards, so we think that the lineage leading to silesaurs and dinosaurs might have had a greater flexibility in diet, and that this could be a reason for their success.' Silesaurs were a group of reptiles which lived through the mid to late Triassic. They were most closely related to the dinosaurs, the relationship being analogous to that between chimpanzees and humans.
It is likely that they diverged from the last common ancestor of the dinosaurs. Yet their mainly herbivorous lifestyle may have been their undoing in contrast to the mainly carnivorous dinosaurs, which explains the early success of the latter.