Musca si dinozaurii
Most leading theories on how dinosaurs died out focus on asteroid impacts or massive volcanism. But a new book blames a much less thunderous force: insects.The rise and evolution of these bugs—the biting disease-carriers, in particular—coincided fatefully with the mighty reptiles’ later days, write George Poinar Jr. of Oregon State University and his wife Roberta in the book, “What Bugged the Dinosaurs? Insects, Disease and Death in the Cretaceous."
The Poinars say the evidence is preserved in lifelike detail, in the form of varied insects trapped in ancient amber.
“There are serious problems with the sudden-impact theories of dinosaur extinction, not the least of which is that dinosaurs declined and disappeared over a period of hundreds of thousands, or even millions of years,” said George Poinar.
He didn’t deny that there is evidence for catastrophic events such as an asteroid strike or lava flows around that time. These “certainly played a role” in the dieoff, but don’t account for its slowness, said Poinar, an entomologist.
On the other hand, he added, “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.” Pests and illness may have subjected T. rex and its scaly kin to a slower torment, but possibly the fatal one ultimately, according to the authors.
The gradual downfall of the dinosaurs came around a period known as the K-T Boundary, between the so-called Cretaceous and Tertiary periods some 65 million years ago. But some dinosaurs survived for thousands of years thereafter, Poinar noted; a number of lineages lived even longer and evolved into modern-day birds.
Poinar and his spouse have spent much of their careers studying plants and animals found preserved in amber, using them to re-create environments of yore. A semi-precious gem that originates as sap oozing from a tree, amber has a unique ability to trap tiny creatures or other materials and preserves them almost perfectly in natural display cases for millions of years. The phenomenon has been invaluable in research; it also formed the premise for the film Jurassic Park, in which fictional scientists extracted dinosaur DNA from amber-trapped mosquitoes.
Insects are believed to have originated more than 400 million years ago from worms, but underwent a major flourishing in the Cretaceous era, when the later dinosaurs lived. The spread of new insect lineages went hand-in-hand with that of flowers, which had mutually dependent relationships with many insects.
This rise of flowering plants was itself bad news for dinosaurs, which traditionally fed on other types of greens, said Poinar. Meanwhile, insects came to compete for some foods with the great reptiles.
But things got worse, Poinar went on. By the late Cretaceous “the associations between insects, microbes and disease transmission were just emerging,” he said. “We found in the gut of one biting insect, preserved in amber from that era, the pathogen that causes leishmania—a serious disease still today, one that can infect both reptiles and humans. In another biting insect, we discovered organisms that cause malaria, a type that infects birds and lizards today.
“In dinosaur feces, we found nematodes, trematodes and even protozoa that could have caused dysentery and other abdominal disturbances. The infective stages of these intestinal parasites are carried by filth-visiting insects.”
In the Late Cretaceous, Poinar said, the world was covered with warm-temperate to tropical zones that swarmed with blood-sucking insects carrying leishmania, malaria, intestinal parasites, arboviruses and other pathogens. These caused repeated epidemics that slowly but surely wore down dinosaur populations, Poinar argued. Ticks, mites, lice and biting flies would have tormented and weakened them.
“Smaller and separated populations of dinosaurs could have been repeatedly wiped out, just like when bird malaria was introduced into
A possible reason why some dinosaurs lived on to make a comeback as modern-day birds, Poinar suggested, is that these smaller animals had a shorter lifespan. That might have helped them evolve faster to adapt to the insect menace, since evolution occurs on a generation-to-generation basis.
“Insects have exerted a tremendous impact on the entire ecology of the Earth, certainly shaping the evolution and causing the extinction of terrestrial organisms,” the authors wrote in their book. “The largest of the land animals, the dinosaurs, would have been locked in a life-or-death struggle with them for survival.”
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