Dawn of the Dinosaurs: Life in the Triassic
Nicholas Fraser, with
illustrations by Douglas Henderson
Proponents of the Cambrian Period can argue with good reason that it was the cradle of metazoan evolution. Fans of the Devonian have claimed that all the major body plans of vertebrates had been established by that time, although the radiations of birds, mammals, and their kin may not have been anticipated 350 million years ago. Students of the Cenozoic acknowledge that the source of many groups sprang from the Late Cretaceous, but that the Paleocene and Eocene witnessed the truly great explosions of mammalian diversity.
Yeaaaahhhhhhhhh, whateverÖ. But mavens of the Mesozoic will argue that the real action is in the Triassic. If you go simply by the traditional Linnean taxonomy of orders and families, nothing on land in the history of vertebrates can compete with the Triassic for sheer diversity. Although it lasted a mere 50 million years or so (251-200 Ma), this period witnessed the recovery from the end-Permian extinction, the last gasps of dicynodonts, the radiation of the two major reptilian diapsid lineages (the lepidosauromorphs and the archosauromorphs), the proliferation of the first synapsids that are sometimes regarded as mammals, and the rise and fall of several dynasties of archaic reptiles and amphibians, to say nothing of old weird fishes, freshwater sharks of several varieties, coelacanths, lungfishes, and various forms that no one still knows exactly where they belong. In short, all the major terrestrial vertebrate body plans were established or exhausted by the end of the Triassic, except the birds. Being in the Triassic is like visiting the intergalactic bar that Luke Skywalker encounters in the original Star Wars movie: the characters look weird but vaguely familiar, the resemblances are usually superficial, you have some trouble figuring out what everyone is saying, and most of them would kill you as soon as look at you.
Now Nick Fraser has published a comprehensive book on the Triassic, one that explains in accessible language the tremendously complex history of this revolutionary interval in the history of life. I donít think there is another book like it for any geological period per se, and it will be a long time before it can be replaced. Reading it is like sitting in a comfortable armchair, experiencing a travelogue of a strange country with a great storyteller and a great photographer. During the Triassic, Pangaea began to split apart; climates changed inexorably and fragmented regionally (it was not simply a matter of becoming hotter and drier worldwide); faunas and floras flourished and dissipated. The global record of Triassic deposits is uneven and ambiguous, so unusual fossil deposits tell us at least as much as the commonly preserved ones. In a sea of parti-colored siltstones, a single boglike pond deposit or a lakebed will record dozens of taxa unknown anywhere else. The amazing thing about the Triassic is that we seem only to be scratching the surface. And Fraser encompasses the knowledge and the wonder of all this in informed, companionable, articulate tones, accompanied by dozens of Doug Hendersonís haunting, evocative paintings.
After a brief introduction to the general types of organisms, the geography, and the initial climatic conditions to be encountered, Fraser organizes his book chronologically and geographically through the Triassic. It is a catalog of strange animals and plants, brought alive by the most recent discoveries and ideas of ecology, functional morphology, and behavior. Wisely, Fraser rejects global generalizations of climatic models in favor of regional and even local reconstructions, led by what the fossils tell us and by his analyses of geographic heterogeneity in temperature, resources, and rainfall. This is one of the strongest features of the book. The rapid replacements, rises and falls of tetrapod dynasties can readily be gleaned from this well-limned catalog, and one has the impression of a series of turnovers as rapid as anything in the Age of Mammals. Many sorts of scientists will benefit from it. Those not familiar with paleontology will get a first-rate, accessible introduction to the dramatis personae; those whose interest tends to focus on the critters will be delighted by the comprehensive introduction to the climatic history, geology, and stratigraphy of the Triassic worldwide. Especially useful is the approach by regions and individual geologic formations: if you want a quick introduction to the Molteno, the Chinle, or the British fissure fill deposits, this book is one-stop shopping.
Inevitably there will be some differences with the editorial approach. The taxonomy used in the book is decidedly old-fashioned, meaning not cladistic; some terms have been out of use for two decades or more, or are used so as to seem paraphyletic when they are not (Reptilia does include birds but does not include basal synapsids; Amphibia does not include all basal tetrapods that are not amniotes). There are no phylogenetic trees of the myriad animals discussed in the book, and so the evolution of groups in this treatment is secondary to the progression of faunas (it is admittedly difficult to tell both kinds of stories at once). The illustrations of actual specimens and their reconstructions in line drawings are almost always without scales, suggesting a more popular approach than an academic one. The photographs of specimens have neither credits nor museum numbers, and seldom are referenced to publications. On the other hand, size can often be inferred from Doug Hendersonís wonderful paintings. And he uses light as beautifully as anyone since Charles R. Knight. One can only hope that generations of children will be similarly influenced and inspired by his art.
Non-specialists who read this book may be a bit nonplussed by the terminologies of stratigraphy, chronology, geology, anatomy, and phylogeny. Fraser provides four appendices and a glossary to help, and he warns you in advance that you may need to recur to these parts first. Ignore him at your peril if you arenít already a Triassic junkie, and then profit from his book for what it is: a great achievement in bringing a most complex interval in the history of life to life, vividly and accessibly. We really needed a book like this, because the Triassic is often overshadowed by the rest of the dinosaur-dominated Mesozoic Era. Its complex and unfamiliar faunas can seem daunting because its menageries are less often the stock in trade of popular books, and so Fraserís text and Hendersonís paintings make this an important and useful book. Hardly anyone will come away from it unenlightened, and it should remain a vital sourcebook on the beginning of the Age of Dinosaurs for many years to come.