Dinosaur systematics and ancient biogeography

This type of research can have interesting, if slightly unexpected, spin-offs. One spin-off that will be considered here links phylogenetics with the geographic history of the Earth. The Earth may in fact have exerted a profound influence on the overall pattern of life.

The geological timescale of the Earth was pieced together through painstaking analysis of the relative ages of sequences of rocks exposed at various places on Earth. One important component that assisted this process was the evidence of the fossils that they contained: if rocks from different places contained fossils of exactly the same type, then it could be assumed with reasonable confidence that the rocks were of the same relative age.

In broadly similar fashion, evidence of the similarity of fossils from different parts of the world began to suggest that the continents might not have been as fixed in their positions as they appear to be today. For example, it had been noted that rocks and the fossils that they contained seemed to be remarkably similar on either side of the southern Atlantic Ocean. A small aquatic reptile Mesosaurus was known to exist in remarkably similar-looking Permian rocks in Brazil and in South Africa. As long ago as 1620, Francis Bacon had M pointed out that the coastlines of the Americas and Europe and | Africa seemed remarkably similar, (see Figure 32d) to the extent £ that it seemed as if they could have fitted together as a pair of gigantic jigsaw pieces. On the basis of evidence from fossils, rocks, and general shape correspondence, Alfred Wegener, a German meteorologist, suggested in 1912 that at times in the past the continents of the Earth must have occupied different positions to the ones they are in today, with, for example, the Americas and Eur-Africa nestled together in the Permian Period. Because he was not a trained geologist, Wegener's views were ignored, or dismissed as irrelevant and unprovable speculations. For all its self-evident persuasiveness, Wegener's theory lacked a mechanism: common sense dictated that it was impossible to move things the size of continents across the solid surface of the Earth.

However, common sense proved to be deceptive. In the 1950s and 1960s, a series of observations accumulated that supported Wegener's views. Firstly, very detailed models of all the major continents showed that they did indeed fit together remarkably neatly and with a correspondence that could not be accounted for by chance. Secondly, major geological features on separate continents became continuous when continents were reassembled jigsaw-like. And finally, palaeomagnetic evidence demonstrated the phenomenon of sea-floor spreading - that the ocean floors were moving like huge conveyor belts carrying the continents - and the historical remnants of magnetism in continental rocks confirmed that the continents had moved over time. The 'motor' that was driving this motion was in effect the heat at the core and the fluidity of rocks in the mantle layer inside the Earth. The theory of plate tectonics that accounts for the movement of continents over the surface of the Earth over time is now well established and corroborated.

From a dinosaur evolutionary perspective, the implications of r plate tectonics are extremely interesting. Reconstructions of past | configurations of the continents, largely based on palaeomagnetics J'

and detailed stratigraphy, indicate that at the time of their origin all e

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