By JOHN VON RADOWITZ
DINOSAURS may have been killed off by biting insects rather
than a cataclysmic meteor impact, a new theory claims.
Disease spread by ancient mosquitoes, mites, ticks
and perhaps even the ancestors of the Scottish midge, was probably what
finished off the reptiles, say scientists.
By changing the nature of plant life on Earth, insects could have made it
harder for dinosaurs to survive.
Bees and other pollinators helped promote the rapid spread of flowering plants
unsuited to the traditional diet of vegetarian dinosaurs. As the plant-eaters
declined, so would their predators.
The theory helps explain why dinosaurs took so long to die off, according to
husband and wife team George and Roberta Poinar.
According to the most widely accepted explanation, the dinosaurs were wiped out
by an asteroid or comet that smashed into the Earth off the coast of Mexico 65
million years ago.
Another theory is that they were driven to extinction by massive volcanic
eruptions in India which led to extreme climate change.
The time at which the dinosaurs disappeared, between the Cretaceous and
Tertiary periods, is known as the K-T Boundary.
But George Poinar, a professor of zoology at Oregon State University in Corvallis,
points out that they did not vanish immediately. Their extinction was drawn out
over hundreds of thousands or even millions of years.
An impact scenario should have led to an abrupt extinction, and volcano-induced
climate change would probably also have wiped them out relatively quickly.
On the other hand, emerging diseases spread by biting insects, combined with
the spread of flowering plants, and competition with insects for plant
resources was "perfectly compatible" with a lengthy process of extinction,
said Prof Poinar.
Insects date back as far as the Carboniferous period, around 300 million years
ago. During the later part of the dinosaurs’ reign, insect numbers and species
exploded. Mosquitoes evolved in the early Cretaceous. The oldest example known,
from Burma, was trapped in amber 100 million years ago. Prof Poinar and his
wife have carried out a study of plants and creatures preserved in amber, the
fossilised resin that is used for ornaments and jewellery.
They outline their dinosaur-extinction theory in a book published by Princeton
University Press, What Bugged The Dinosaurs? Insects, Disease And Death In The
Cretaceous.
Prof Poinar said: "During the late Cretaceous period, the associations
between insects, microbes and disease transmission were just emerging.
"We found in the gut of one biting insect
preserved in amber from that era, the pathogen that
causes leishmania – a serious disease today, one that can infect reptiles and
humans. In another we discovered organisms that cause malaria, a type that
infects birds and lizards today.
"In dinosaur faeces, we found nematodes, trematodes and even protozoa that
could have caused dysentery and other abdominal disturbances. The infective
stages of these parasites are carried by filth-visiting insects."
He said that during this period, the world was covered with warm-temperate to
tropical areas, swarming with blood-sucking insects. The infections they
carried would have caused epidemics that slowly wore down dinosaur populations.
"Smaller and separated populations of dinosaurs could have been repeatedly
wiped out, just as when bird malaria was introduced to Hawaii, it killed off
many of the honeycreepers," Prof Poinar added.
The full article contains 557 words and appears in
The Scotsman newspaper.
Scientist 