14 January 2008

Did bugs bring down the dinosaurs?

Cosmos Online
Tiny biting insects may have played a role in the downfall of the dinosaurs, by spreading disease and changing the prehistoric flora, argues a new book.
Did bugs bring down the dinosaurs?

Bite me: A Cretaceous-era tick found in amber from Burma. This tiny insect and its kin may have had a role in bringing down the dinosaurs. Credit: Poinar

BRISBANE: Tiny biting insects may have played a role in the downfall of the dinosaurs, by spreading disease and changing the prehistoric flora, argues a new book.

What Bugged the Dinosaurs? – authored by palaeontologists and amber fossil experts at Oregon State University in Corvallis, U.S. – details a new theory that insects were a major force in the slow decline and eventual extinction of dinosaurs over millions of years.

“Competition with insects, emerging new diseases and the spread of flowering plants, over very long periods of time, is perfectly compatible with everything we know about dinosaur extinction,” co-author George Poinar told Cosmos Online.

Ancient plagues

Dinosaurs disappear from the fossil record around 65 million years ago, at the end of the Cretaceous period. Most of the evidence points to a major asteroid or comet impact linked to a planet-wide mass extinction.

Now, Poinar suggests that the rise and success of insects may have also been a factor in that decline. His evidence comes from the study of ancient disease and parasites in the fossil record.

By working with insects preserved in amber, Poinar has found ancestors of the insect-borne pathogens that today cause, malaria, leishmaniasis and trypanosomiasis, in addition to evidence of viruses. His painstaking work has also turned up the remains of intestinal worms and the cysts of protozoan parasites in dinosaur coprolites (fossilised faeces).

The argument is that faced with these newly evolved parasitic enemies, dinosaurs fared poorly due to their slow development, large body size, low reproductive rates and long lives. In the end, Poinar said, it would have been difficult for dinosaurs to compete, compared to smaller, fast-breeding animals, in which the bugs would have found it more difficult to get a toehold.

“After many millions of years of evolution, mammals, birds and reptiles have evolved some resistance to these diseases. But back in the Cretaceous, these diseases were new and invasive, and vertebrates had little or no natural or acquired immunity to them,” he said. “Massive outbreaks causing death and localised extinctions would have occurred.”

Changing flora

“We can’t say for certain that insects are the smoking gun, but we believe they were an extremely significant force in the decline of the dinosaurs,” added Poinar. “Our research with amber shows that there were evolving, disease-carrying vectors in the Cretaceous, and that at least some of the pathogens they carried infected reptiles. This clearly fills in some gaps regarding dinosaur extinctions.”

Along with co-author Roberta Poinar, he suggest that insects would also have played a role in changing the composition of the plant communities on which some dinosaurs relied for food. Insects developed mutually beneficial partnerships with flowering plants, helping them to reproduce – and out compete the then dominant conifers, cycads and relatives. To exacerbate the problem, herbivorous insects would also have been major competitors for the food.

“It is an interesting theory that we can take into consideration when we examine the extinction of the dinosaurs,” said palaeontologist Robert Jones at the Australian Museum in Sydney, Australia. However, it will be hard to prove either way, he added: “It’s not as simple as a lot of people think… insects haven’t generally been thought of as a major cause of extinction.”

Dinosaur expert Steve Salisbury at the University of Queensland, in Brisbane, urged caution, however. “The book implies that we have detailed knowledge of events leading up to the extinction events – but we really don’t know whether dinosaurs were in demise up to that point,” he said. “There is good evidence to suggest that many plants and animals did suddenly die out.”


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