George Poinar Jr., a professor of zoology at Oregon State University, said one of the problems with sudden impact theories of dinosaur extinction is that dinosaurs declined and disappeared over a period of hundreds of thousands of years.

"That time frame is just not consistent with the effects of an asteroid impact," Poinar said Thursday in a release. "But 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."

The concept is outlined in the new book "What Bugged the Dinosaurs? Insects, Disease and Death in the Cretaceous," by George and Roberta Poinar.

"We don't suggest that the appearance of biting insects and the spread of disease are the only things that relate to dinosaur extinction," Poinar said. "Other geologic and catastrophic events certainly played a role. But by themselves, such events do not explain a process that in reality took a very, very long time, perhaps millions of years. Insects and diseases do provide that explanation."