[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.]


    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
    primitive tetrapods.

    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

    Crash Course

    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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