The general established view seems to be that birds evolved from dinosaurs, but what did dinosaurs evolve from

�

�

Q.� What did thecodonts look like

A.� Because this is a period with scant fossil evidence, relatively little is known about the thecodonts. Unlike dinosaurs that walked on their toes, thecodonts walked on the flat of their foot.

�

Q.� When did dinosaurs start evolving

A.� Around 235 to 240 million years ago, during the Triassic period. It is a period of evolution about which there is little evidence and which has generated sharp debate among palaeontologists. A small, bipedal thecodont is the probable ancestors of dinosaurs.

�

Dinosaurs developed a more upright posture than thecodonts, with legs under their bodies rather than out at the side like lizards, giving them much greater mobility.

�

Several different kinds of dinosaurs developed from the thecodonts, most of which are divided into two major groups based on their anatomy. The first group, the Saurichians or lizard-hipped dinosaurs, included all the flesh-eating types and a few of the giant plant-eaters. The second group, the Ornithichians or bird-hipped dinosaurs, were herbivores.

�

Q.� How long did the thecodonts last for

A.� By 190 million years ago the thecodonts, other existing reptiles and the emerging mammals had been outclassed by the dinosaurs. Dinosaurs remained the dominant land-dwelling animals until they died out at the end of the Cretaceous period, 65 million years ago.

�

Q.� Where does the word fossil come from

A.� From the Latin word 'fossilis', which means 'dug up'.

�

Do you want to know about an animal's evolutionary history Click here to ask.

�

by Lisa Cardy