"Long before it's in the papers"
August 03, 2010

RETURN TO THE WORLD SCIENCE HOME PAGE

Did insects take down T. rex?

Jan. 4, 2008
Courtesy Oregon State University
and World Science staff

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.” 

A Cretaceous-era insect preserved in amber (courtesy G. & R. Poinar)

Most leading theories on how dinosaurs died out focus on asteroid impacts or massive volcanism. But but a new book blames a tiny, much less thunderous force: insects. Their rise and evolution—the biting disease-carriers in particular—coincided fatefully with the later days of the mighty reptiles, 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 their evidence is captured in almost lifelike-detail, in the form of varied insects preserved in amber dating to the extinction era. “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. There is evidence for catastrophic events such as an asteroid strike or lava flows around that time. These “certainly played a role” in wiping out the dinosaurs, Poinar continued, but he insisted they don’t account for the slowness of the process. 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.” Insects and disease may have subjected the reptiles to a much slower torment, but it might have ultimately been the fatal one, 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 the 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 a natural display case for millions of years. The phenomenon has been invaluable in research; it also formed the premise for the film Jurassic Park, which related a tale of scientists extracting 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. Flowers themselves were bad news for dinosaurs, which had traditionally fed on other sorts of plants, 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 Hawaii, it killed off many of the honeycreepers,” Poinar said. “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.” 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.”