George Poinar, Jr. and Roberta Poinar. 
Princeton University Press, Princeton, NJ
2008; 264 pp.
ISBN-13: 978-0-691-12431-5
Price $30 (hard cover)

Modern vertebrate populations aren’t unique in being plagued by insects, parasites, and viruses. The discoveries by George and Roberta Poinar of developmental stages of protozoa and an “ancient malarial organism” preserved in the guts of insects fossilized in amber confirmed that these disease-causing organisms were also important components of paleoecosystems. These revelations are products of years of dedicated work and form the fundaments of the Poinars’ argument in What Bugged the Dinosaurs?, a book that attempts to support a significant role for insects and diseases in the extinction of the non-avian dinosaurs at the boundary between the Cretaceous and Paleogene periods. This extinction hypothesis is thought-provoking, and the book contains fascinating photographs of amber fossils, but ultimately the authors’ thesis is weakly supported.

Three amber localities [Lebanon (~130 Ma); Myanmar (~100 Ma); and Alberta, Canada (~75Ma)] provide the insect fossils that the authors use to build their argument. Largely omitted from the book are major Cretaceous deposits with abundant insect records, including Liaoning Province (limestone, China, ~130 Ma); New Jersey (amber, USA, ~100 Ma); and Santana (limestone, Brazil, ~100Ma). Given the importance of amber specimens for our knowledge of extinct arthropods and for the Poinar’s thesis, a review of the process of amber fossilization would have been a welcome addition to the early chapters of the book.  

The Poinars portray insects and dinosaurs in adversarial terms—dinosaurs “would have been locked in a life-or-death struggle with them for survival” (p. 5)—and they use this antagonistic relationship to develop the hypothesis that insects and the diseases they vectored were important causative agents for the mass extinction of dinosaurs.  The authors develop their case by presenting evidence that Cretaceous invertebrates had three major negative impacts on dinosaur populations: as competitors for food plant resources, as parasites, and as vectors for disease.

Evidence for dinosaur-insect competition for food is presented in an extensive list of major Cretaceous plants and insect herbivores that may have been associated with them, as indicated by their presence in contemporaneous amber pieces. A more thorough review of dinosaur and insect co-occurrence in the fossil record would have added strength to this argument. The Poinars use seven chapters to address their numerous discoveries of parasitic arthropods and the disease-causing organisms they may have vectored to dinosaurs. These discoveries are vividly described and include interesting and easy-to-read biological accounts of their modern counterparts. For example, Paleoleishmania, the polyhedra associated with polyhedrosis viruses, was discovered in the guts of sandflies preserved in Burmese amber.

Unfortunately, the association of insect, plant, virus and dinosaur fossils does not provide compelling evidence for the extinction hypotheses laid out by the authors. While present-day insect populations also compete for food resources with herbivores, modern habitats, such as the Serengeti (Tanzania and Kenya), support high levels of invertebrate diversity and large numbers of herbivorous mammals.

The authors argue that because blood cells found in the protozoan-infected sandflies are consistent with “reptilian” blood cells and the dominant “reptiles” at the time were dinosaurs, then the newly-discovered disease agents likely plagued the dinosaurs. They cite the work of Robert Desowitz, who “suggested that an epidemic of reptilian kala azar [a type of leishmaniasis] transmitted by sandflies could have caused the extinction of the dinosaurs” (p. 201) and they indicate that the identification of these protozoa provides the “smoking gun” that Desowitz lacked. It would be benighted to claim that dinosaurs did not suffer from such infectious diseases and parasites but, while the identification of these preserved pathogens is fascinating science, the associative reasoning presented by the Poinars falls short of providing a convincing causative agent for mass extinction.

The dinosaur information presented in “What bugged the dinosaurs?” is largely inaccurate. The taxonomy is particularly confused, with genera elevated to families (e.g. “dryosaurids,” p. 29), incorrect common names used (e.g. “ceratopsids,” p. 29), and nonexistent taxonomic entities (e.g. “coelurids,” p. 31). Some of the ecological roles attributed to dinosaurs are also in error or based on outdated information. For example, the text makes references to now-debunked ideas, such as tail-dragging sauropods (p. 47), and gliding (but not flying) pterosaurs (p. 44).

Important concepts in dinosaur paleobiology are expounded in the book that are either unsupported (no references provided) or contradict existing research. Dinosaurs are characterized as “the ultimate K-strategists” (p. 191), yet they actually epitomize the opposite by laying large numbers of eggs, exhibiting fast growth to adulthood, retaining long life spans, and in some cases exhibiting extended parental care. Given that biting insects are essential to the book’s hypothesis, the statement that “dinosaur skin was surprisingly thin and … very similar to that found on… Gila monsters” (p. 107) is particularly troubling. While illustrations of the surface of some dinosaur skin are shown, this critical point has no citations to support it and the fossilized skin of some dinosaurs has been shown to be quite thick.

After conceding that dinosaurian populations would have been weakened by environmental factors such as the Deccan Traps eruptions in India, lowering sea levels, and the impact at Chicxulub, the authors conclude that we "cannot discount the probability that diseases, especially those vectored by miniscule insects, played an important role in exterminating the dinosaurs," (p. 202) – a considerable diminution of their original statement in the preface. While most extant vertebrates harbor parasites and suffer from insect-borne pathogens, few populations are driven to extinction because of these infestations. It is perhaps more unreasonable still to suppose that two entire orders of reptiles with a global distribution were wiped out by disease — we know that disease resistance evolves relatively quickly and that most parasites are host-specific. The authors do not address either of these obvious counterarguments effectively. At the end of the book, one gains an appreciation for the role insects played in paleoecosystems, but is left with very little convincing evidence to support the idea that insects and diseases played a pivotal role in the pseudoextinction of the dinosaurs.

Although the main hypothesis of the book is weakly supported, What Bugged the Dinosaurs? has several redeeming qualities. The insect work the Poinars cite is fascinating and publicly little-known, such as studies on dung beetles and on parasites found in coprolites. Interactions between arthropod and dinosaurs remain understudied and the book serves to prompt more thought on this interesting subject. Further work on this topic would be enriched by a more accurate understanding of the Dinosauria. The invertebrate fossil record clearly has much left to contribute to our understanding of ancient ecosystems.

Jorge A. Santiago-Blay
Resident Research Associate
National Museum of Natural History
Smithsonian Institute
Washington, DC
E-mail: blayj@si.edu

Jonah Choiniere
The George Washington University
Washington, DC

David W. E. Hone
Institute of Vertebrate Palaeontology & Palaeoanthropology
Beijing, China
Editor’s Note: G. O. Poinar, Jr. served as Major Professor of Santiago-Blay at Berkeley, a fact of which the book review editor was fully aware.
 

American Entomologist
Vol. 55, No. 3, Summer 2009