An inevitable biological consequence of this intrinsic (Earth-bound) process of continental sundering is that the once cosmopolitan population of dinosaurs became progressively subdivided and isolated. The phenomenon of isolation is one of the keystones of organismal evolution - once isolated, populations of organisms tend to undergo evolutionary change in response to local changes to their immediate environment. In this instance, although we are dealing with comparatively huge (continent-sized) areas, each of the continental fragments carried its own population of dinosaurs (and associated fauna and flora); each of which, with the passing time, had the opportunity to evolve independently in response to local changes in environment, stimulated by, for example, progressive changes in latitude, longitude, adjacent oceanic currents, and prevailing atmospheric conditions.

Logic dictates that it must clearly have been the case that tectonic events during the Mesozoic affected the scope and overall pattern of the evolutionary history of dinosaurs. Indeed, it seems perfectly reasonable to suppose that the progressive fragmentation of ancestral populations over time must have done much to accelerate the diversification of the group as a whole. Just as we can represent the phylogeny of dinosaurs using cladograms, we could also represent the geographic history of the Earth through the Mesozoic Era as a series of branching events as continental areas separated from the 'ancestral' Pangaean Earth. Of course, this general approach is a simplification of true Earth history because, on occasion, continental fragments have coalesced, welding together previously isolated populations. But at least as a first approximation, this provides a fertile area for investigating some of the larger-scale events in Earth history.

If this model of the natural history of dinosaurs were generally true, M we might expect to be able to detect some evidence in its support by | probing the details of the fossil record of dinosaur species, and the £ tectonic models of continental distribution through the Mesozoic. This type of approach has been developed in recent years to probe for coincident patterns in the evolutionary history of dinosaurs and whether their evolutionary history is echoed in their geographic distribution.

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