Dinosaur Plague: Expert Q&A

Q: Is there a way to check for immune responses to disease in the remains of the dinosaurs? Laura Strebel, Ogden, Utah

Poinars: Not yet possible. We feel that the diseases bloodsucking insects carried back then were new for dinosaurs and resistance had not yet been established.

Q: Dr. Robert Bakker's 1986 book The Dinosaur Heresies first brought forth the notion of disease playing a large role in the dinosaurs' extinction. With the recent revelation of insects aiding with disease propagation (from your recent book What Bugged the Dinosaurs?), do you think any correlations between specific insects (and the diseases they brought) and decimation of particular dinosaur lineages can be determined? Scott Anderson, Moon Township, Pennsylvania

Poinars: Bakker, as well as others before him, speculated that dinosaurs had diseases. However, I don't think he said diseases played a role in their extinction, at least in his book. Also, at that time there was no evidence that diseases existed back then. All dinosaurs originated from a common ancestor (monophyletic), so they all would have had a similar type of immune system, which had to be a good one. However, even good immune systems can be overwhelmed with new, multiple pathogens.

Q: Are you able to compare the DNA of some of these germs? Or is the DNA gone after all this time? Guy Kuhn, San Gabriel, California

Poinars: We have only been able to obtain DNA from insect tissues in amber. The germs are too small to attempt DNA extraction, so we have to go by their shape, size, and other characteristics.

Q: What have you found since the NOVA filmmakers filmed you? Any new fascinating discoveries you'd like to share? Anonymous

Poinars: Our search for microbes led us to discover the oldest case of mutualism in the fossil record, a number of symbiotic protozoa from a 100 million-year-old termite. That study was recently published in the journal Parasites and Vectors (see www.parasitesandvectors.com/content/2/1/12).

Q: I live in New Jersey and have collected Cretaceous amber with insects and other inclusions. Is it possible that my specimens could help answer some questions about the extinction of the dinosaurs? Daniel Gitler, Middlesex, New Jersey

Poinars: Certainly. If you have any bloodsucking insects in your collection, you may want to examine them for pathogens.

Q: How do you know how old the insect in the amber is—1,000 years or 1 million years or from when the dinosaurs were alive? Thanks. Meredith Edwards, Richardson, Texas

Poinars: Geologists date the amber by looking for other (index) fossils in the surrounding sediment. In this case, all of our biting insects with pathogens were dated between 97 and 110 million years.

Q: Any way to match the reptilian blood cells you've found in amber to a specific kind of dinosaur? Thanks. Anonymous

Poinars: Unfortunately not. They are just reptilian cells, and nobody has characterized dinosaur blood cells, so we cannot say for sure if they are dinosaur blood cells or those of another reptile. However, most biting flies will feed on a range of vertebrates in one group, and we feel that even if these blood cells were from a non-dinosaur, the same flies were biting dinosaurs also.

Q: Were dinosaurs particularly susceptible to diseases during the extinction event, or were other organisms also vulnerable? Is it possible that some mass extinction events other than the one that occurred at the end of the Cretaceous could have had a pathological cause? Can any evidence be found in amber for such a cause contributing to these other extinction events? Brian Beaty, Yarmouth, Massachusetts

Poinars: Certainly all organisms had diseases. However, amber with insects only goes back 135 million years, so we can't say anything about earlier extinction events. Dinosaurs were susceptible, since we feel that the vector associations only started in the Cretaceous, and these would have been new diseases, which the dinosaurs had not experienced previously. It would have been like measles and mumps wiping out the Amerindian populations when first contacted by Europeans.

Q: How can we be sure that the mandibles of the insects could penetrate the very thick hides of the dinosaurs? Ed Kreusser, Corvallis, Oregon

Poinars: Dinosaurs had what are called tuberculate scales, which are adjacent (not overlapping) and expose a small area of skin between them. Biting flies could have fed through the thin skin between the scales. Biting flies feed on present-day reptiles with such scales (Gila monster, etc.).

Q: Are there examples of a species going extinct as a result of parasites carried by a vector such as the sandfly? Anonymous

Poinars: Native birds in Hawaii have become extinct from malaria vectored by an introduced mosquito.

Q: I can see that insects evolving in conjunction with flowering plants would become vectors for dinosaur diseases, but why couldn't dinosaur evolution keep up? Sylvia Richman, Davis, California

Poinars: These diseases were new on the scene, since we feel vertebrate pathogen-vector associations only began in the Cretaceous. Some of the dinosaurs might have had time to develop resistance to one or more pathogens, but the combination of leishmania, malaria, and trypanosoma, along with intestinal worms, protozoa, and environmental stress, was just too much for their immune systems.

Q: What is your next amber project? Alex Brown, Berkeley, California

Poinars: We will continue to search for parasites and pathogens in amber. A colleague and I have a book in press on fossil behavior (Fossil Behavior Compendium), and we show mating insects, insects depositing eggs, and insects producing flatulence in amber. Other behavioral patterns of animal and plant life in all fossil settings, marine and terrestrial, are also covered.