[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Penguin post script

> 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. [...]
> _Tonsala hildegardae_ and _Copept[e?]ryx titan_

How much of a fool do I make of myself when I ask whether these are in
reality plotopterid pelicans? Full-blown penguins are known from the Eocene
of Seymour Island.

> 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."

Does he mean the man-sized penguins of the Eocene like *Anthropornis*? (In
which case I could accept that, but I could probably also invoke the
Eocene-Oligocene mass extinction.)

> 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).

Maybe you shouldn't exclude the moa- and (according to Maori tales)
man-eating *Harpagornis moorei*. Anyway, penguins breed on the coasts of
southern and western South America, South Africa and southern Australia
where heaps of predators exist.

> 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?

The second part of your sentence means that seals and penguins are _not_ in
competition. :-)

> 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),

Plotopteridae en masse.

> 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.

Seals and penguins often have different food requirements. For example, many
or all penguins eat lots of krill, AFAIK no seals do.

> This hypothesis assumes that mammals are superior to
> dinosaurs.

What? _In general_???

The climate is getting stranger and stranger. In late December and early
January, when the "Christmas defrost weather" has become normal,
temperatures regularly reached down to -10 °C, then we got late spring with
temperatures regularly reaching up to +20 °C, then (after unusually strong
winds) came early spring, and today we've surprisingly received a centimeter
of snow. TV sez the Gulf Stream has already weakened by 20 %.