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Re: Limbs and niche partitioning



Hi Dino List,

Hmmm... is this some how connected to the origin of bipedalism in dinosaurs?
If so consider the aquatic ape theory of Elaine Morgan which seeks to
explain human bipedalism by postulating that a group of LCAs between humans
and chimps was isolated on an island roughly in the Afar Triangle c. 6-4
mya. They adapted to a partially aquatic life style and when the Afar dried
up the now bipedal apes rejoined their African cousins.

Why did they become bipedal? Well it's only in water that the African apes
will habitually walk upright - bonobos do so in flooded forests, gorillas do
so to cross streams, and Proboscis monkeys [not African or apes, but roughly
the same size] walk bipedally in their tidal forest habitats. Otherwise most
primates are quite happy getting about on all fours.

Sure gibbons and orangs are semi-bipedal on tree branches, but when on the
ground they don't bipedal for long. Bipedalism seems to only really work
when you're off the ground [in the water or in the trees] or when you're
committed to it by anatomy [us and dinos it seems...] Someone mentioned
Oreopithecus in another thread - it was bipedal and its remains are found in
lacustrine deposits. It was also probably isolated on an island.

continued below...

----- Original Message -----
From: dbensen <dbensen@gotnet.net>
To: <Patrick.Norton@state.me.us>
Cc: dinosaur list (comment line) <dinosaur@usc.edu>
Sent: Friday, October 01, 1999 11:12 AM
Subject: Re: Limbs and niche partitioning


> >>One niche that opened up was the aquatic environment.  Just a thought
> (wildly speculative), but perhaps some of the prerequisites of flight
> (feathers and a flapping ability) evolved in response to cursorial
> dinosaurs exploiting an aquatic environment.  The higher heat transfer
> rate and higher density of water would likely result in stronger
> selective response to adaptations affecting insulation or propulsion,
> lift and drag, particularly in smaller animals---and without the
> hypertrophy of arms or other elements required for aerial flight. Once
> those characteristics evolved, exapting them for aerial flight would not
> seem to be as big a step as going directly from the ground to the air.  I
> wondered about this as I thought about Sinornithosaurus, which apparently
> couldn't fly but had integumentary fibers of some sort and a shoulder
> girdle capable of a flapping motion.  As I said, wildly speculative.
>
> <<
>
> I believe Greg Paul said something like that in Predatory Dinosaurs, that
is,
> that early birds (archaeopteryx in particular) may have lived like
dippers.
> I've never heard the theory attached to Sinornithosaurus, but it sounds
> intriguing.  the animal can't be larger than some penguins.  Does it have
the
> conical teeth of fish-eaters?
>
> Dan
>
Humans also have some thermoregulatory features not seen in the other apes -
we sweat more than they do, and we sweat a lot more salt, have subcutaneous
fat and yet oddly have lost a lot of hair. All suggestive of a semi-aquatic
phase in our evolution when some features mattered less than others, and yet
are survival critical if we evolved in say the mythical savannah...

As for dinosaurs well maybe they had an aquatic phase that emphasised
hind-leg development over front. Perhaps the Ornithosuchids were more croc
like than we suspect, living up to the name. One flaw in my biological
analogy maybe the fact that sitting on a tree branch makes one semi-erect,
when you're a primate. I can't quite imagine what the archosaur ancestor of
dinos was doing that could be equivalent.

Adam