I was intrigued by dinosaurs as a child. They were so majestic and powerful, part of a fantasy world I could never quite imagine. This book attempts to answer the question of how they became extinct. George and Roberta Poinar propose that microbes played an important role in the demise of the dinosaurs at the end of the Cretaceous. Their evidence centres around three amber deposits made between 135 and 80 million years ago which provide a plethora of fossilized insects that have recently been found to contain pathogenic microbes. The process of fossilization is selective and an incomplete record causes problems. However, the authors explain how the evidence supports their hypothesis.

By comparing insects fossilized in amber to those that exist today, palaeontologists can determine the likelihood of pathogens being present. In an 'intricate case of detective work', the Poinars first discovered pathogenic microbes in a fossilized sand fly, along with vertebrate blood cells. Today, blood-sucking insects are a major source of disease. The authors suggest that things were not so different in the Cretaceous. Dinosaurs had surprisingly thin scales with small openings, and the spaces between scales offered them even less protection against insects. Even if the skin proved difficult to penetrate, the areas around the mouth, eyes, ears and nose would have been much more accessible.

The amber deposits suggest that biting midges were quite common in the Cretaceous. Morphologically, the fossilized creatures are related to reptile biters, so the authors suggest they may have fed on dinosaurs. They suggest that an allergic reaction to a bite could have led to scratching, which can cause bacterial and fungal infections and could be life-threatening. The amber deposits also provided researchers with evidence of a Cretaceous malarial parasite, Paleohaemoproteus, which could have caused a fatal infection in dinosaurs. Black flies carried the malarial parasite Leucocytozoon and mosquitoes, horseflies, ticks and fleas may also have transmitted disease. The authors suggest that emerging contagious diseases may have spread among dinosaur populations.

Dinosaurs may also have been affected by microbes indirectly. Plant diseases would have depleted the food supply, potentially causing herbivores to starve. Although initially this would have provided carnivores with easy prey, they too would eventually have starved.

Some of the chapters begin with a description of a fictional (but possible) scenario. Although some of these paint a vivid picture, they can distract the reader from the story and are sometimes difficult to read because they are so packed full of adjectives. Nonetheless, they show the enthusiasm the authors have for the subject, as do the numerous personal anecdotes in the text.

The extinction of the dinosaurs is hotly debated, primarily swinging between two schools of thought: that the extinction happened quickly (catastrophists) versus slowly (gradualists). The arguments are explained well at the end of the book, although some clarification may have been useful earlier in the text.

Readers with little prior knowledge of palaeontology may find some chapters hard-going - continuous references (with no explanations) to types of dinosaurs, time periods and prehistoric trees can stagnate the flow of the narrative. Appendix C is a useful resource for readers not trained in the science, as it shows the problems associated with palaeontological evidence and evaluating the fossil record. Unfortunately, an incoherent order makes an otherwise comprehensive reference list difficult to use.

Insects are central to this book, with a whole chapter dedicated to explaining how they managed to survive when all the dinosaurs died out. In my opinion, the story of the microbes is somewhat neglected and some mistakes creep in. A chapter on insects as sanitary engineers explains how, without insects to decompose excrement and cadavers, the Cretaceous world would have been almost uninhabitable. The authors applaud termites for their good job at keeping things clean, but do not refer to their essential endosymbionts! The important role of microbes as decomposers is also not acknowledged sufficiently.

I would certainly recommend this book to anyone interested in dinosaurs and prehistoric life in general. It has changed the way I imagine the Cretaceous and the extinction of the dinosaurs and I am sure it will open up new avenues of thought in this area.