'Vegan' dinosaurs' tale of success

Flesh-eating Tyrannosaurus rex may be the most well-known and iconic dinosaur, but it turns out some of the most successful of these prehistoric reptiles were actually vegetarian.

A new study from the University of Bristol, led by Eddy Strickson, has presented clear evidence about how plant-eating dinosaurs evolved.

In the rich dinosaur deposits of North America, hundreds of skeletons of plant-eaters are found for every T. rex. But how did they survive and proliferate? Was it down to innovation or stimulus by plant evolution?

Eddy Strickson said: "The plant-eating ornithopods showed four evolutionary bursts; one in the middle of the Jurassic, and the other three in a cluster around 80 million years ago in the Late Cretaceous. This was down to innovation in their jaws and improved efficiency."

Plants were evolving fast during the Mesozoic, with the rise of cycads, conifers, and especially the angiosperms or flowering plants in the Cretaceous. However, the evolution of ornithopod dinosaur jaws and teeth did not show any response to these changes in availability of plants.

Co-leader Albert Prieto-Marquez said: "Some of the immensely successful duck-billed hadrosaurs of the Late Cretaceous might have been eating flowering plants, but their tooth wear patterns, and especially close study of their coprolites - that's fossil poops - shows they were conifer specialists, designed to crush and digest the oily, tough needles and cones."

Co-leader Tom Stubbs added: "Our work has been done using new methods of evolutionary analysis. Up to now, many evolutionary studies of this kind have been quite circumstantial, but we have been able to identify times of intensive evolution using objective, numerical methods."

Over 150 million years, many hundreds of dinosaurs came and went, but in the end they all died out 66 million years ago. The new work helps confirm another recently published, and controversial, claim that most dinosaurs were already in decline 40 million years before the meteorite struck and finished them off.

The research is published in Scientific Reports.