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Re: Penguin post script



Generally, the first it true. Foraging and energetics of modern penguins
is generally well known. There is at least one excellent monography of
penguins and account on penguins in Del Hoyo et al. vol.1. Modern penguins
are not effective long-distance swimmers and require cold waters which are
more productive. About predators: penguins nest on shores of Patagonia and
S Africa, for example.

Jerzy

On Sun, 24 Feb 2002, John Bois wrote:

>
> Once upon a thread there was a discussion of why penguins are almost
> exlusively southern hemisphere species.  I came across a new book called
> Aquagenesis (The Origin and Evolution of Life in the Sea) by Richard
> Ellis.  He reviews the penguin fossil record and notes that putative
> penguin ancestors of the Oligocene did exist in the northern
> hemisphere.  He also quotes Olson and Hasegawa (1996--ref. if needed) as
> saying that "there is a strong possibility that the disappearance of
> (large penguins) is linked with the ascendancy of seals and porpoises."  I
> thought I would plug these ideas into the competition between the
> following hypotheses for the strange distribution of extant penguins:
> 1) Penguins are unable to access northern waters because they evolved in
> the south and are completely dependent on cold water currents, none of
> which ever cross the equator.  The equator thus serves as a barrier to
> penguin radiation northward.  If penguins or their close ancestors once
> lived and bred in the north, this is a questionable hypothesis.  But this
> depends on the status of _Tonsala hildegardae_ and _Copeptryx titan_.
> 2) Southern continents have fewer and/or less effective predators.  This
> enables the existence of these highly vulnerable species (they are the
> only obligatory terrestrial egg-laying species that depends entirely on
> the sea for its food--true?).  Antarctica and NZ have no land-based
> predators (I'm excluding avian predators because they are roughly
> constant for N. and S.hemispheres).  With a couple of exceptions, other
> southern continental breeding sites are on offshore or off-continent
> islands.  In the northern hemisphere, the coast of Asia, Europe, and
> North America, all possess effective predators.  However, there are also
> off-shore islands in the north.  This hypothesis must account for penguin
> absence here as well.  And so...another hypothesis: during ice ages,
> northern ice sheets extend to islands off those continents and allow
> predator access from source continents.  Southern ice sheets must extend
> further to reach continents.  This provides an isolated refuge that
> (since the Miocene????) has been consistently available through
> evolutionary time.  In times of warming, marine access to predatorless
> terrestrial continental regions persists in the south (i.e., Antarctica
> has inhospitable terrain further south than northern hemisphere islands
> are north).  In this respect, I would like to invoke seals and co.  Is it
> possible that seals and penguins are in direct competition for breeding
> sites, but that penguins parents, eggs and chicks can tolerate harsher
> conditions than seal neonates?
>
> To encapsulate my favored hypothesis: In terms of evolutionary time,
> penguin habitat is ephemeral in the Nth.  This is reflected both in the
> lack of diversity in penguin analogues (e.g., the Great Auk), and in the
> absence of northern radiation of penguins themselves.  And the global
> distribution of seals is a problem for the equatorial barrier
> hypothesis.  It assumes that the swimming, foraging, and navigational
> abilities of aquatic dinosaurs are inferior to that of sea-going
> mammals: seals are able to cross the equatorial barrier, penguins are
> not.  This hypothesis assumes that mammals are superior to
> dinosaurs.  Such an absurd claim should be rejected out of hand.  Can I
> get a witness?
>
>