Friday, February 6, 2009
Early palaeontologists thought dinosaurs must have been slow and sluggish to have lost the "evolutionary race" to birds and mammals. Modern studies find no sign that they were laggards, lazily dragging their tails behind them.
Most dinosaurs were probably as mobile as large, modern mammals. Like lions, meat-eating dinosaurs were active predators that probably lay down and rested after eating their fill.
One study in 2000 of an exceptionally well-preserved hadrosaur fossil, found in a South Dakota riverbed, suggested that dinosaurs had powerful hearts more like those of birds or mammals than modern reptiles. Researchers argue that the fossilised, four-chambered heart points to an active, bird-like metabolism.
Terrestrial reptiles reached 5 metres in length before the first dinosaurs evolved 230 million years ago. Some - such as sail-backed Dimetrodon, which flourished in North America during the Permian period (290 to 240 million years ago) - were related to dinosaurs, but were not true dinosaurs.