[Paleopsych] NYT: Evolution Update: Heavy Breathing in an Early Ear
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Sun Jan 29 21:01:17 UTC 2006
Evolution Update: Heavy Breathing in an Early Ear
[It's the earbones that constitute the earmarks distinguishing mammal from
reptile. Here's another clue about how the transition could have taken
place. Two other observations, well worth reading, appended.]
By HENRY FOUNTAIN
Forget that adage about how you've got to walk before you can run. In
evolution, it might be more appropriate to say that you've got to
breathe before you can hear.
Scientists in Sweden have filled in a piece of an evolutionary puzzle:
how the middle ear developed in tetrapods, four-limbed creatures.
The answer, they report in the journal Nature, is that before the
middle ear became part of the auditory system, its precursor might
have been part of the respiratory system.
The researchers, Martin D. Brazeau and Per E. Ahlberg from Uppsala
University, base their claim on a study of a fossil of Panderichthys,
a 370-million-year-old fish that is an immediate ancestor of the most
The fossil has an enlarged spiracle, a passageway between the jaw and
the top of the head, as well as other changes that represent a middle
ground between the relatively simple structures of more ancient fish
and the complex morphology of tetrapods.
"It's got this combination of fish- and tetrapod-like features," said
Mr. Brazeau, who undertook the research as part of his work on a
doctorate in evolutionary biology.
Scientists have known since the 19th century that in tetrapods,
including humans, the middle ear develops from an embryonic structure
called the first gill arch. In fish, the first gill arch forms the
support for the jaws including the spiracle.
In fish that are ancestral to Panderichthys, the spiracle is small. In
Panderichthys, Mr. Brazeau said, "the first thing that happens is that
the spiracle becomes very large." Further alterations follow, he said,
including changes to a bone that is the forerunner of the stapes, or
stirrup bone, that is part of the middle ear structure.
So the Panderichthys fossil, which was found in Latvia, is a useful
snapshot of a moment in evolution. But why do the researchers suspect
that the spiracle was part of the fish's breathing system?
Part of the answer can be found in modern bottom-dwelling marine
creatures like rays. When they are on the sea floor, rays use
spiracles on the top of the head for breathing instead of their
mouths, to avoid sucking up sand. Panderichthys, Mr. Brazeau said, may
have been a bottom dweller and have had the same need for an alternate
respiration route. "It may very well have had its face in the mud," he
The space age has spawned a lot of things - global communications,
precise weather forecasts and Tang, to name a few - but it has also
generated a lot of junk. More than 11 million pounds of orbital debris
are now being tracked, including old satellites, pieces of exploded
rockets and smaller items like astronaut gloves.
All that space junk poses a collision threat to current and future
space missions, manned or robotic, government or commercial. And just
about every new launching adds more debris.
But as a review of the situation in the journal Science points out,
the problem has taken on a life of its own as well.
The review, by J. C. Liou and N. L. Johnson of NASA's Johnson Space
Center, notes that simulations show that over the next 200 years, the
number of pieces of debris will continue to increase, even without
more rocket launchings.
That's because existing pieces will occasionally collide, producing
fragments that will outnumber other debris that has burned up in the
A few collisions have already occurred, including one a year ago
between a 1970's-vintage American rocket body and a piece from a
Chinese rocket that exploded in 2000.
The NASA scientists point out that the worst area for collisions is a
band from about 550 to 625 miles up. The density of debris in this
band is higher because, among other reasons, larger rocket stages are
used to push satellites to this altitude, and it takes longer for
orbits there to decay.
The NASA scientists say that suggested methods of disposing of the
junk - by attaching tethers to fragments, for example, to increase
drag and speed up orbital decay - are not economically feasible. New,
cheaper technologies are needed, they say.
Light, Action, Birdsong
Early risers are familiar with a phenomenon of the avian world, the
tendency of many birds to sing at first light. No one knows exactly
why this dawn chorus occurs, but there are several theories.
One is that as birds become active at that time of day, they don't
have enough light for foraging. So the birds use their considerable
energy to engage in social communication instead.
If light availability is important, then different birds should begin
chorusing at different times, depending on several factors. Species
that live high up in the canopy of trees should begin singing sooner
than those near the forest floor, where there is less ambient light.
And species with larger eyes, which can see better in low-light
conditions, should sing earlier, too.
Karl S. Berg of Florida International University and colleagues tested
the effect of these factors in a tropical forest in Ecuador.
Dr. Berg, now at the University of California, Berkeley, recorded
singing times for 57 species, including many songbirds.
The findings, reported in Proceedings B, a journal of the Royal
Society, showed that in songbird species, height in the trees and eye
size did affect when singing started.
In nonsongbirds, however, there was less of a correlation. The
researchers say that this may be because the nonsongbird species
studied have varying diets, with some eating fruits that are easily
seen in low-light conditions. Most songbirds eat insects, which remain
hard to see until conditions get lighter.
Belts of Their Own
The existence of the Kuiper Belt, that vast band of icy and rocky
objects beyond Neptune that includes Pluto and Quaoar, was confirmed
only about a decade ago. But now astronomers from Berkeley and the
Goddard Space Flight Center have discovered what they think are
similar belts around two other stars.
Using the Hubble Space Telescope, they observed debris disks around
the stars, both of which are about 60 light-years away. The finding is
being reported in Astrophysical Journal Letters, and images are at
Debris disks have been found around about a half-dozen other stars,
but these two systems are older - so it is more likely that the disk
has settled into a stable configuration, like the Kuiper Belt.
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