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PALEONEWS: bat lungs and echolocation
This is a CNN custom news article.
CNN has changed formats so I can not give you the URL.
I recommend registering at cnn.com for your own
custom news to access the article online- -Betty
Among the various orders of mammals, Chiroptera (Greek for hand-wing)
stand alone. That is, they fly alone, for bats are the only mammals with
true powered flight. How bats got to be bats is still mysterious, but in
spite of the lack of clear evidence for their remote ancestry, bats are
here, and becoming better understood.
Bat fossils (compared to dinosaur remains, for instance) are relatively
few, probably because most bats are small, with bodies that are not
preserved easily. The best bat fossils, from Germany and Wyoming, were
preserved because the bats apparently fell into lakes, were not eaten,
and were covered with sediment that eventually hardened.
Many fossilized bats are represented only by their teeth and sometimes
their jaws. Nevertheless, there are fossils of recognizable bats that go
back 50 or 60 million years to the early Eocene period of the current
Eocene bats are very much like the 925 species of modern bats identified
so far. No obvious intermediate form has been found yet, although many
scientists believe that the ancestors of bats were living and perhaps
flying 70 million years ago in the last age of the dinosaurs, when our
primate ancestors were small and stupid.
A bat, like us, is an "advanced" mammal that conceives and nurtures its
fetus inside its body because the baby is attached to a placenta --
unlike marsupials (such as kangaroos) whose tiny young crawl out of the
body into an external pouch, or monotremes (such as the duck-billed
platypus) that lay eggs.
All bats have big chest muscles to power the wings made of membranes
between their very long fingers, in front of the arms, and between the
hind limbs and the rear (tail or buttock). The hooked claws on their
toes make it easy for bats to assume their usual resting position --
Bats are usually classified into the Megachiroptera (megabats) and the
Living only in the Old World, megabats have fox-like faces with
prominent eyes and excellent vision. Most of them eat nectar and fruit,
using the claws on each wing's thumb and index finger. In the Central
Park Zoo there are six big fruit bats that usually hang from trees or
the ceiling, occasionally thrilling awed visitors by flying from one
tree to another over their heads.
A few years ago there was a flurry of excitement over the theory that
megabats were closely related to us primates -- because we both have
brains high-wired for vision. Alas (it would be nice to have a flier in
the family), it seems we are not related except as fellow mammals.
The zoo also has an enclosed exhibit of microbats which possess only one
finger claw, and are active because the exhibit is kept dim to seem like
night. Microbats keep track of where they are and what's around them by
echolating -- sending out high-pitched sounds so that the echoes
reflected from objects tell the bat where the object is.
The zoo's microbats fly above a large turtle that lives in one of the
pools below, perhaps eating Central Park's invading mice instead of
falling bats. Wild microbats (the common 'little brown bat') live in
Central Park itself, occasionally seen by admirers like me, or by
terrified people who think these bats may be vampires. They are not.
Studying microbats, scientists once thought that the ability to echolate
developed even before the ancestor of bats was able to fly. The
scientists thought that echolation took so much energy that it had to
develop first, enabling the animal to find insects easily, before it
could become a flier.
This theory now seems unlikely because John Speakman, at Scotland's
University of Aberdeen, has shown that when a bat flies, its flight
muscles squeeze the rib cage and force air up through the larynx. This
enables the bat to send out the sounds required for echolation while
it's flying, with no extra use of energy. It seems logical that the
evolution of flying came first, and echolation later.
Nancy Simmons, at New York's American Museum of Natural History, thinks
that the ability to echolate evolved mainly in microbats because they
hunted night-flying insects or night-blooming flowers, and that the few
megabats able to echolate evolved it independently.
Icaronycteris, the most primitive fossil bat of 53 million years ago,
was probably able to echolate but not as well as modern bats because its
inner ear was housed in an only moderately enlarged cochlear bone.
Emma C. Teeling, at Queen's University of Belfast, and her colleagues,
have analyzed bat relationships "using DNA sequence data from four
nuclear genes and three mitochondrial genes." This DNA analysis proved
the lack of common ancestor between bats and primates, including those
master gliders -- the "flying" lemurs.
Teeling also found that the microbat superfamily Rhinolophoidea (found
in the Old World) is more closely related to megabats than it is to
other microbats. Perhaps some ancestral bats became large,
vision-dependent fliers and lost the ability to echolate. This seems to
me more likely than the idea that Rhinolophoidea microbats developed
echolation independently of other microbats.
Simmons thinks that the bat ancestor probably had large hands with
membranes between the fingers. Membranes are useful for holding things
like fruit or prey (and are used this way by some modern bats).
Membranes also make gliding a snap, and, eventually, became wings.
However bats became bats, they are fascinating. More on this next time.
(c) 2000, Los Angeles Times Syndicate
Flying Goat Graphics
(Society of Vertebrate Paleontology member)