The ascent of the dinosaurs to the throne of the animal kingdom may have been more gradual than previously believed, scientists say.
Fossil discoveries dating from about 215 million years ago show some of the earliest dinosaurs lived for millions of years side-by-side with related animals long seen as their ancestors and precursors, scientists report in the journal Science.
Many scientists thought these reptiles - very much like dinosaurs, but more primitive - died out around the time of the appearance of the first true dinosaurs, which were dog-sized beasts not giants, roughly 230 million years ago.
This pattern -- certain types existing long before they became dominant -- seems to be far more common. Mammals have been found much earlier lately as well. It probably does have archaeological/anthropological implications; we tend to think of evolutionary changes in human physiology and culture as happening pretty quickly. E.g., someone invents something really great -- like agriculture -- and it immediately takes off because it's so much better, more fit, etc. But what we usually find is that most traits have precursors much earlier that failed to become populous until some point that they really take off. Which makes some sense from a Darwinian perspective: you have a certain amount of variation present in any population, and when the selective environment changes, certain variants are selected for and increase in frequency.
My pet theory of agriculture used to be -- maybe still is? -- that cultivation was present at low frequencies all over the place, but population pressure eventually provided the conditions that selected for it. Which might explain why settled agricultural communities took much longer to develop in the New World as opposed to the 1000-odd years in the Old World: the later colonization of the Americas caused population levels to take longer to reach a critical point where intensive agriculture became selected for on a wide scale.
I should point out that this is similar to what the systems theorists were saying 30 years ago. In their scenario, population pressure led groups of people to start developing agriculture. I think that tends more towards intention as a cause rather than simple variation/selection.