A new primitive dinosaur species, Eocursor ("early runner") parvus ("small"), discovered in South Africa, seems to be the missing link in the dinosaur evolution.

The small, agile plant-eater lived in the Late Triassic, about 210 million years ago, before the emergence of the huge Jurassic beasts.

Eocursor seems to be one of the most primitive Ornithischia dinosaurs. Ornithischia groups the majority and most evolved of the herbivororous dinosaurs, like horned dinos (type Triceratops), armored dinosaurs, Iguanodons, plated dinosaurs (Stegosaurus) and duck billed dinosaurs.

The fossil was first found in 1993 but only recently appraised.

It is much more complete than other Triassic ornithischian dinosaurs found by now, comprising skull and bones of the backbone, arms, pelvis and legs.

The Eocursor is a little bigger than a fox and its bone structure and light shape point to a swift creature.

The new fossil offers the earliest evidence on the origins of many skeletal traits seen in the ornithischians, including the backward-pointing pelvis (bird-like pelvis, hence the name ornithischia).

The other dinosaurs (carnivores, from which birds and huge vegetarian sauropods emerged) are called saurischia, due to their pelvis which is similar to that of the lizards.

Ornithischians were quite rare in Late Triassic but boomed subsequently in the early Jurassic, filling empty herbivorous niches left by mass extinctions. "We know ornithischians were a very successful and important group of plant-eating dinosaurs that first appeared 220 million years ago, in the late part of the Triassic Period," explained Dr Richard Butler, a palaeontologist at the Natural History Museum, London, UK.

"Eocursor is a very small and primitive dinosaur that would have eaten plants with its leaf-shaped teeth and had an unusually large, grasping hand. The lower leg bones are very long, suggesting it would have been able to run fast on its hindlegs to escape from predators."

"The earliest dinosaurs we know are about 228 million years old, so this one is only just a bit younger than that," commented Dr Paul Barrett, a NHM researcher not involved in this research. "The fossil record for early meat-eating dinosaurs is slightly better; and for some of the other plant-eaters, we also have not-too-bad a record. But for the ornithischians, we have almost nothing; so in that sense, this is a major find," he told BBC News.