Re: Why Were Prehistoric Insects Huge?


"Joe" <abc@xxxxxxx> wrote in message news:KS6vi.35$hK5.34@xxxxxxxxxxx
Insects now are limited in size by birds who prey on them- 300 million
years ago there were no birds.

I've heard that sceanrio before. Not sure what data backs it up. Recent
findings (posted in this thread) indicate that the breathing aparatus of
the large insects back then were much more complex than today's insects,
allowing them to utilize more of the 35% O2 contained in the atmosphere at
the time, and allowing them to grow to a larger size. Once the O2 levels
receded, those larger organs became a liability rather than an advantage,
and the larger insects died out. Considering that they have now imaged
those organs in detail on fossil insects, and have the oxygen isotope data
in hand, I think the evidence for this hypothesis is compelling.

George


"George" <george@xxxxxxxxxxxxxxx> wrote in message
news:7oxui.7345$2v5.2321@xxxxxxxxxxxxxxxxxxxxxxxxx
http://www.sciencedaily.com/releases/2007/08/070806112323.htm

Science Daily - Alexander Kaiser, Ph.D., of Midwestern University's
Department of Physiology, Division of Basic Sciences, was the lead
author in a recent study to help determine why insects, once
dramatically larger than they are today, have seen such a remarkable
reduction in size over the course of history.

"There were hundreds of ideas to explain the small size, but none of
them could be proven," Dr. Kaiser said. To test their theory that it was
an insect's respiratory system that limited its size, he and his
colleagues launched an extensive study using beetles and fruit flies.

The study, much of which was performed at Illinois' Argonne National
Laboratory, involved the examination of various beetles' respiratory
systems, using new x-ray beam technology to help determine how they
breathe.

Findings show that Dr. Kaiser and his colleagues are on the right track
in their theorizing. Insects breathe through a network of air filled
tubes that deliver oxygen directly to the cells. These tracheal tubes,
especially in the leg, take up more room in larger beetles.

"More than 300 million years ago, there was 31 to 35 percent oxygen in
the air," Dr. Kaiser said. "That means that the respiratory systems of
the insects could be smaller and still deliver enough oxygen to meet
their demands, allowing the creatures to grow much larger."

Dr. Kaiser and his team plan to conduct similar studies in the future
using more ancient species such as dragonflies, since beetles and fruit
flies are considered relatively "new" species in comparison.

Note: This story has been adapted from a news release issued by
Midwestern University.





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