Dinosaurs, Spitfires, and Sea Dragons
When, as often happens, I find myself dissenting from something written by Stephen Jay Gould, I remind myself that we share a common childhood experience. We were both dinosaur nuts, at a time when to be interested in dinosaurs was to be an oddball. For both of us, that early passion has led to a life spent thinking about evolution, although in my case a world war, and a false start as an aircraft engineer, meant that I did not become a professional biologist until I was thirty; However, our paths diverged earlier. When I was eight, my father died, and we moved away from London to the country: for me, visiting the Natural History Museum was replaced by watching birds. I suspect that this switch may help to explain the disagreements between us, to which I shall return below. It also explains why I can review two books about dinosaurs only as an interested outsider, and not as an expert.
The two books are very different in intent. The Dinosauria is a joint effort by several experts, aimed at professionals, summarizing the current state of dinosaur research. Dinosaurs, Spitfires, and Sea Dragons is aimed at a wider readership, but one prepared to make some effort. It attempts to deduce how dinosaurs lived, mainly by comparing them with animals alive today.
Current research on dinosaurs, although it forms the basis of speculations on how they lived, is not in the main concerned with that question. Obviously, the major effort is devoted to discovering and describing the fossils themselves. I was impressed to learn that almost half the known genera of dinosaurs have been discovered during the last twenty years. The interpretation of these fossils is primarily aimed at recognizing anatomical similarities and differences, and arranging the specimens into a natural classification. These, of course, have been the main preoccupations of comparative anatomists for over two hundred years. Today, a “natural classification” is usually taken to mean one that reflects evolutionary history. If species are grouped together in a “taxon” (that is, a genus, family, order, or what have you), the implication is that the taxon includes all species, and only those species, descended from a common ancestor. In the jargon of the trade, the taxon is “monophyletic.” Anatomists, however, were seeking a natural classification long before they accepted a theory of evolution, and their methods were little altered when they did come to accept the theory. For some reason I do not understand, they usually assumed that a natural classification must be a hierarchical one—that is, species must be grouped into genera, genera into families, families into orders, and so on. Of course, natural classifications do not have to be like that: one need only mention Mendeleyev’s periodic table of the elements. But if species arose by a branching process of evolution—that is, if species split into two, but do not join again—then the natural classification is indeed hierarchical.
At this point, I must declare a …