What Bugged the Dinosaurs? Insects, Disease, and Death in the Cretaceous

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I grew up with a fondness for dinosaurs. Their unbelievable size, their peculiar shapes, and their undeniable absence from the world as I knew it were all sources of fascination. But never once did I think of the dinosaurs as being plagued by biting insects and other blood-sucking arthropods; mosquitoes, flies, ticks and mites were creatures that haunted camping trips, picnics and attics, not the majestic dinosaurs! But according to the new book, What Bugged the Dinosaurs? Insects, Disease, and Death in the Cretaceous by George Poinar, Jr., and Roberta Poinar, my view of dinosaurian life needs some serious rethinking. This book is based on the authors' lifetime of research in paleoentomology -- research that inspired the blockbuster movie Jurassic Park -- where they identify the remains of arthropods that were trapped in amber during the Cretaceous Period (between 65.5 and 145.5 million years ago), and use this information to develop their premise that disease-carrying biting insects and arachnids drove the dinosaurs to extinction.

Based on examining ancient invertebrates trapped in amber, scientists have a clearer view of the web of life that existed during the Cretaceous, as described in the first ten chapters of this book. They know, for example, that the ecology of the Cretaceous world was more complex than that of today because there was more floral and faunal biodiversity then. They also know that Cretaceous arthropods filled many important ecological roles by pollinating flowers and by serving as a major food source for many dinosaurs and other animals. Insects and arachnids also competed with dinosaurs for food by eating plants and they often fed directly on dinosaurs' blood, flesh and feces. Further, by carefully examining the blood in these amber-preserved invertebrates, it is known that biting insects and arachnids spread a variety of viruses, bacteria, fungi and parasites that cause diseases that are still very dangerous today, such as malaria, dysentery, yellow fever and leishmania, just to name a few.

Much of this knowledge is suppported by research carried out by the Poinars. Based upon meticulous analyses of numerous amber specimens collected from Lebanese (dating from 130-135 mya), Burmese (99-105 mya), and Canadian deposits (77-79 mya), the authors develop their main theme; the Cretaceous was a warm, moist world filled with voracious swarms of biting insects that transmitted deadly diseases that could have caused the demise of the dinosaurs. While acknowledging that an asteroid impact brought a catastrophic end to the Cretaceous and the non-avian dinosaurs, the authors ask;had the dinosaurs already been staggering towards extinction due to the combined effects of deadly diseases, parasitic infestations, and intense competition with insects?

To this end, the Poinars find that ancient arthropod mouthparts were adequate for dining on dinosaur blood and flesh, regardless of the microstructure of the dinosaurs' skin and whether they were warm- or cold-blooded. I was especially fascinated with the authors' discovery of blood preserved in the guts of these noxious pests, which appears to be dinosaur blood. Further, and even more tantalizing, they have electron micrographs of blood infected with different vertebrate pathogens, suggesting that ancient arthropods acted as vectors even 100 million years or more ago, spreading deadly disease organisms throughout the population.

After describing the beneficial (to dinosaurs) role of arthropods during the Cretaceous, the Poinars add detail to their argument in chapters 11-19. They begin by describing the benefits of feeding on blood, and then they focus on specific blood-feeding arthropod groups; biting midges, sand flies, mosquitoes, blackflies, horseflies and deerflies, fleas and lice, ticks and mites, and then they discuss parasitic worms that live within ancient vertebrates. They move on to describe their discovery of Cretaceous diseases (especially Paleoleishmania proterus and Paleohaematoproteus burmacis, which are accompanied by electron micrographs) in ancient biting insects and provide an overview for the evolution of pathogens. Oddly, they erroneously mention that Plague is caused by a Rickettsia (Plague is caused by the bacteria, Yersinia pestis).

The Poinars then devote a chapter to comparing and contrasting the different natural history characteristics employed by the dinosaurs versus the insects and how they affect survival (also listed in a table in Appendix B) and, in the next chapter, they discuss how these characteristics make insects the ultimate survivors. Certainly, as the authors note in the last chapter of the book, insects passed through the K/T boundary relatively unscathed, whereas the dinosaurs obviously did not.

This accessible book is written for the general public. Several of the chapters begin with a speculative vignette that describes the relationship between dinosaurs and Cretaceous arthropods, or describing how a particular insect came to be encased in amber. The book also contains plenty of drawings and photographs (don't miss those delightfully disgusting eye worms!), including a special section in the middle of the book that has 66 color images of animals trapped in amber described in the Poinars' research. The 264-page book ends with three appendices; Appendix A lists all the Cretaceous Hexapoda that were known to exist, noting which of these were identified in the amber deposits that the Poinars examined; Appendix B is a table that lists specific characteristics that contribute either negatively or positively to the survival of terrestrial animals; and Appendix C briefly discusses the problems associated with evaluating the fossil record and extinctions. These appendices are followed by a 27-page list containing 349 references that will keep the interested reader occupied with plenty of reading material, and an 11-page user-friendly index.

Even though the data presented in the book do not adequately support the authors' premise that dinosaurs were driven to extinction by biting insects that spread infectious diseases through their populations, I think this is an interesting argument and it is plausible that disease at least contributed to the ultimate demise of the dinosaurs. I recommend this book, especially to dinosaur fans and to those who like to read about infectious diseases and their arthropod vectors. Libraries will find this well-written book is a popular addition to their list of available titles.

George Poinar, Jr., is currently in the Zoology Department at Oregon State University. He is well known internationally in various fields, including paleobiology, nematology, and insect pathology. He became familiar with tropical diseases while serving as a consultant for the United Nations and World Health Organization. Roberta Poinar is a retired research scientist. They are the coauthors of The Amber Forest: A Reconstruction of a Vanished World (Princeton) and The Quest for Life in Amber. Their research has been featured in leading publications worldwide and on television programs such as Nova.

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Coincidentally, we just saw the Nova program Jewel of the Earth (a "David Attenborough show") on Thursday on the subject of organisms preserved in amber, and it featured interviews with Drs. Poinar. Always a fascinating subject ...how timely :)



By Chardyspal (not verified) on 12 Apr 2008 #permalink

The premise is interesting I am reminded of the impact of the tsetse fly in Africa. Houston residents from June 2001 will certainly recall the Biblical plague of mosquitoes that followed upon the 14 inches of rain from T.S. Allison. Locals here who explore the history of Indian settlements along the SE TX Gulf Coast learn that the Indians coated themselves in mud to escape the ferocious attacks of marsh mosquitoes. In the Cretaceous the climate was warm and tropical and thus buggy nearly worldwide, so being a dinosaur was likely not much fun. Has anyone been to the alaskan interior in the summer; I hear the prevalence of standing water breeds so many biting bugs that one can spot a large mammal some distance away by the cloud of insects assaulting it, so you don't need Mesozoic heat to breed insect pests. Imagine a Triceratops trying to scratch a bug bite (probably have to assault a tree to get relief on some parts of its body). However, the dinosaurs must have evolved a standoff with their ailments; don't most pathogens settle into a less virulent form over time while simultaneously immunity builds up in the host?

By biosparite (not verified) on 12 Apr 2008 #permalink

Aagh! It's Sunday morning, and I'm thinking about evolutionary epidemiology! :-)

I'm sceptical about the central thesis: pathogens and dinosaurs co-existed for ling enough to have reached an equilibrium (rabbits and myxoma managed it in a few decades in Australia). It's a pity - the book sounds fascinating.

bob, using rabbits and myxoma as your example is not correct: rabbits can breed when they are as young as six months of age -- unlike dinosaurs, which are thought to have begun breeding somewhere between five and twenty years old. however, humans show a similar breeding strategy to dinosaurs and they seem to have developed an inherent resistance to malaria (for example).

I the rabbit-myxoma system, it was the myxoma that evolved to become less virulent. There's a classic paper by May and Anderson that show the change (I'll have to dig out when I'm at work). I suspect that the effect would be stronger in longer-lived species, because it takes longer to replace the killed individuals, so local extinctions will reduce the global fitness of the more virulent pathogens.

It's a fascinating area, because of the interaction of population and evolutionary dynamics. Especially when both become spatial...

I think this is an interesting argument and it is plausible that disease at least contributed to the ultimate demise of the dinosaurs.

I was thinking the same thing throughout this post and was going to say something but you made it a good conclusion here. I've always hated "science" (and history) that tries the "everything you know is wrong and here's what really happened" approach. We have new data, and new data created a bigger picture (increased volcanic activity, possible difficulties digesting newer flowering plants), but the data that supported the older picture is still there and can't be blithely put aside.

By Joe Shelby (not verified) on 13 Apr 2008 #permalink

oops. the aside in the last paragraph was attached to the wrong spot. should have read:

We have new data, and new data created a bigger picture, but the data that supported the older picture (increased volcanic activity, possible difficulties digesting newer flowering plants) is still there and can't be blithely put aside.

By Joe Shelby (not verified) on 13 Apr 2008 #permalink

well, bob, it's actually questionable as to how a virulent disease would affect long-lived and slowly-reproducing species such as dinosaurs since the disease could potentially wipe out those species before they have a chance to recover (reproduce, evolve resistance, etc).

note that i am not arguing that the book's premise is correct because i think there is no way to truly demonstrate this satisfactorily for the dinosaurs, but i am thinking along the lines of other modern species that could be lost due to the effects of newly emerging diseases on the rampage.

I agree diseases could wipe out a species, but I don't think you would see a signal of it in the geological record, because it would happen so quickly. I'm also sceptical about it wiping out all dinosaurs: that's not the way epidemics usually work.

It's a pity, it sounds like the authors are over-reaching themselves with this thesis, when it's already really cool that we can reconstruct the ecology of the dinosaurs down to their sores.

Much of this knowledge is suppported by research carried out by the Poinars.

I like the post, but that typo just nagged at me a bit. ^_^;