The extinction of the dinosaurs is an iconic event in Earth history that attracts continued attention from scientists and the public. Just when everyone thought that the case was closed and a giant meteorite implicated, as expressed in a ‘manifesto’ statement last year in Science (Schulte et al. Reference Schulte, Alegret and Arenillas2010), signed by 41 distinguished authors, it turns out that everything is not so clear, as explained by Archibald et al. (Reference Archibald, Clemens and Padian2010), signed by an equally distinguished list of 29 authors. David Archibald's book reflects this somewhat cautious stance. He has lived through the brouhaha about the KT impact, and has been a constant commentator over the past thirty years, drawing evidence from his own field of vertebrate palaeontology, and especially from the small mammals that lived during the last days of the dinosaurs. In a previous book (Archibald, Reference Archibald1996), the vertebrate palaeontological case was put, and here it is brought up to date.
This is a slim volume of six chapters, which review, respectively, what is known of the last 10 million years of the dinosaurs, the Cretaceous mammals, the origin of modern mammalian groups, the records of different groups through the KT boundary, possible causes of diversity decline in latest Cretaceous time, and finally the current position on dinosaurian extinction and especially the radiation of the mammals.
Archibald's case rests strongly on his oft-argued case that dinosaurs, and other vertebrate groups such as turtles and mammals, were declining in abundance and diversity through the last 5 m of sediments of the Hell Creek Formation, representing the last 100,000 years of the Cretaceous. Whether this is a global pattern or not is widely debated. His other forte has been the Late Cretaceous mammals, and especially those that are close to modern mammalian clades. Archibald outlines the debates between palaeontologists studying sometimes incomplete remains and experts on modern mammals. He has witnessed, and been instrumental in, major revisions in methods; palaeontologists are now much more critical about assigning fossils to modern clades.
As noted at the start, opinion is divided on whether the KT impact was the sole cause of mass extinction, or a contributor. The evidence for the impact is clear, and the story of how the evidence was assembled is a fascinating story of science in action. But, as Archibald says, nobody addresses the question of just how the physical crisis caused the exact patterns of extinction that we see in the rocks. Most physical killing models arising from impact would be so devastating that all life should have succumbed, and yet it did not. Further, the Deccan traps were erupting through this interval, and geologists cannot ignore them while at the same time arguing that other basalt traps caused mass extinction at the end of the Permian and at the end of the Triassic (through global warming, acid rain, and ocean stagnation).
This is a learned essay, written clearly and attractively for students and the public, but supported by substantial footnotes and referencing for the professionals. Some of the illustrations are familiar, but there are many original images, including the exquisite pencil drawings of Mesozoic mammals by Maria Gonzalez. If like me you had filed the KT event away in your mind as ‘impact and nothing else’, this book will remind you that the case is much more complex.
