From: Joe.Morlan@f501.n914.z8.rbbs-net.ORG (Joe Morlan)
Newsgroups: rec.birds
Subject: Bird evolution
Date: 10 Apr 92 17:44:00 GMT


  ***** On 04-09-1992, Ian Christopher maione wrote *****

ICM>    I'm not familiar with the specifics of penguin evolution,
ICM> but they are birds, so I would assume they evolved from a
ICM> flighted bird somewhere up the evolutionary chain somewhere.
ICM> I suppose it's possible they might come from a long line of
ICM> flightless birds, but that doesn't seem that likely.  Anyone
ICM> know anything about that?

In one popular scenario the penguins are an offshoot of the
Procelariformes (tube-nosed swimmers) which include albatrosses
and other strong flyers.

Flightlessness has evolved many times in various groups of birds.
It is particularly common in island ecosystems where birds may
not need flight to avoid predators.  There are energetic
disadvantages to flight, so those populations that lost that
ability might be better able to withstand food stress and might
be better able to survive in the long-term.

All modern flightless birds are believed to have evolved from
flying ancestors.  In the case of penguins, one can see a similar
development of the wing in the northern hemisphere alcids.
Penguins and alcids are ecologically very similar although not
related at all.  Both have evolved long narrow wings to act as
flippers for swimming under the water. Wings of this shape are
fairly poor for flying through the air, so alcids have reached a
compromise where they fly, with great effort.  However, there are
several fossil and recently extinct flightless alcids, e.g. the
Great Auk.

All penguins are flightless.  Their wings are even narrower than
those of most alcids, and penguins are much more agile in the
water than alcids.  E.g. penguins are able to "porpoise" in and
out of the water and alcids cannot.  There is little question
that penguins evolved from a flying ancestor.  In fact I am
unaware of any modern flying bird which is believed to have
evolved from a recent flightless ancestor.

ICM>  The main evidence comes from the analysis of the skeleton
ICM>  of a creature dug up from the upper Jurassic period, called
ICM>  Archaeopteryx Lithographica, which is essentially a small
ICM>  theropod with feathers.  It is a "missing link" between
ICM>  dinosaurs and birds, having both bird characters (i.e
ICM>  feathers and wings) and dinosaurian characters (i.e teeth,
ICM>  long tail, small claws on the wings).

The limestone imprints of the feathers of Arechaeopteryx indicate
that it could fly.  The outer primaries are asymmetric, a feature
found only on modern flying birds.  Modern flightless birds have
symmetric wing feathers.  However, Archaeopteryx lacked the
keeled sternum which anchors the large pectoral muscles of modern
flying birds.  So it is not clear if Archaeopteryx was capable of
flapping flight.  My view is that it probably was an excellent
glider.

ICM>     Recently (I'm not sure whether this has been published
ICM> yet) there was also a discovery of another possible bird
ICM> ancestor from the late Triassic period (quite a bit earlier
ICM> than Archaeopteryx) dubbed "Protoavis", which has thrown a
ICM> bit of a twist into the issue.  However, Protoavis has some
ICM> characters (i.e a four-toed foot) which suggest that it is
ICM> not as close it birds, and it is certainly possible that
ICM> flight might have evolved more than once, with only one line
ICM> surviving to become modern birds.

I've heard of this, but don't know the details.  However, most
modern birds have four toes, so I don't understand why this
character would mean it was not close to birds.  Modern birds
with fewer than four toes are believed to have lost the extra
toes in their evolutionary development.  How many toes did
Archaeopteryx have?

--Joe Morlan, Albany, CA


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