Vegetarians may have led the dinosaurs out of obscurity and into 140 million years of global dominance. Remains of two of the earliest known species of "terrible lizard" are helping vertebrate palaeontologists tackle one of the great mysteries of evolution - what heralded the age of the dinosaurs?
Research at the University of Bristol hints that while the first dinosaurs were most likely fast-moving man-sized reptiles that ate cockroaches and other small creatures, the plant eaters that soon evolved from them may have held the key to the species' ultimate success.
Michael Benton, a professor at the University of Bristol, believes the two creatures - one un-earthed in the United Kingdom, the other in Brazil - will give scientists a better idea of the origins of herbivory among the dinosaurs.
Scattered bones of Thecodontosaurus antiquus were found beneath what is now a suburb of Bristol. It was widely believed they were lost in 1940 to wartime bombing.
Professor Benton has been able to reassemble surviving pieces that were hidden away in specimen drawers. His updated description of the dinosaur, a slender, bipedal beast some 2.5m long with a long neck and tail, will appear in the Journal of Vertebrate Paleontology in March.
Saturnalia tupiniquim was similar to, though somewhat smaller than, Thecodontosaurus and was first described towards the end of last year after three skeletons were unearthed in Brazil.
As the most primitive Sauropodo-morphs ever found, dating back some 230 million years, they are the ancestors of the giant plant eaters such as Diplodocus and Brachiosaurus but were vastly outnumbered by other herbivorous reptiles such as the Rhynchosaurs and Dicynodonts.
Yet they kept a foothold, possibly by carving out a specialist role, such as being able to feed off vegetation unpalatable to or unobtainable by their contemporaries.
Professor Benton believes that what-ever it was that allowed them to hang on, it gave them the opportunity to take over once fate in the form of a catastrophic climate change had removed most of those rivals in the late Triassic period, 220 million years ago.
"It is not clear what those first plant-eating dinosaurs were doing, but it allowed them to overcome the hurdles of becoming herbivorous before that extinction event gave them their chance to prevail," said Professor Benton.
The field was clear for the descendants of Thecondontosaurus and Saturnalia. When another, greater extinction event heralded the Jurassic age, the dinosaurs were poised to dominate the planet.