Friday, January 4, 2008

Insects caused dinosaur extinction?

A new study by scientists has suggested that dinosaurs might have been wiped off the face off the Earth by biting, disease-carrying insects over a long period of time.

According to the study, the rise and evolution of insects, especially the slow-but-overwhelming threat posed by new disease carriers, could have been an important contributor to the demise of the dinosaurs.

The evidence for this emerging threat has been captured in almost lifelike-detail in the form of various insects preserved in amber that date to the time when dinosaurs disappeared.

As a semi-precious gem that first begins to form as sap oozing from a tree, amber has the unique ability to trap very small animals or other materials and – as a natural embalming agent – display them in nearly perfect, three-dimensional form millions of years later.

"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," said George Poinar Jr., a courtesy professor of zoology at Oregon State University.

"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," he added.

These facts make the authors of the study argue that insects provide a plausible and effective explanation for the slow, inexorable decline and eventual extinction of dinosaurs over many thousands of years. This period is known as the famous "K-T Boundary," or the line between the Cretaceous and Tertiary Period about 65 million years ago.

In the Late Cretaceous period, the world was covered with warm-temperate to tropical areas that swarmed with blood-sucking insects carrying leishmania, malaria, intestinal parasites, arboviruses and other pathogens. These insects caused repeated epidemics that slowly-but-surely wore down dinosaur populations.

In fact, ticks, mites, lice and biting flies would have tormented the giant reptiles and weakened them considerably.

According to Poimar, back in the Cretaceous, these diseases were new and invasive, and vertebrates had little or no natural or acquired immunity to them. Massive outbreaks causing death and localized extinctions would have occurred, he said.

Also, insects could have spread plant diseases that destroyed large tracts of vegetation, and they could have been major competitors for the available plant food supply.

"We don’t suggest that the appearance of biting insects and the spread of disease are the only things that relate to dinosaur extinction," said Poinar. "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," he added.

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