Dinosaurs Diversified Over Time, Not Suddenly

July 23, 2008 -- The belief that dinosaurs underwent explosive species diversification just before they were wiped out is an illusion, for the beasts' main evolutionary shifts took place millions of years before, a study says.

The strange demise of the dinosaurs at the end of the Cretaceous era some 65 million years ago has given rise to a popular view that almost has the tinge of Greek tragedy.

Just as the rulers of the Earth had reached their evolutionary zenith, a catastrophic event -- possibly a space rock that slammed into Earth -- brought the curtain down on their long reign.

Scientific support for this view comes the number of dinosaur fossils dating from a period called the Cretaceous Terrestrial Revolution, between 125 million to 80 million years ago, when Earth's book of life was changed forever.

During this epoch of riotous biodiversity, flowering plants, social insects, butterflies, modern groups of lizards, mammals, and possibly birds, too, all emerged.

Some experts have suggested that dinosaurs were also part of the show, as so many weird fossils, such as duckbilled hadrosaurs, horned ceratopsians, pachycephalosaurs and other wonders, date from this time.

But a new study, published on Wednesday in a British journal Proceedings of the Royal Society B, says that dinosaurs were less than a sideshow in the DNA spectacular.

Researchers led by Graeme Lloyd of the University of Bristol, western England, devised a "supertree" of dinosaur evolution, patiently analyzing how more than 450 species -- about 70 percent of the known finds -- developed.