Re: An alternative to ST and AAT

Phillip Bigelow (
Sat, 02 Nov 1996 20:23:01 -0800

Paul Crowley wrote:
> In article <01bbc7cd$7d98a740$c92270c2@default>
> "John Waters" writes:
> JW> Why does bipedalism need special justification? It happened
> JW> in Dinosaurs, Birds, Kangaroos and Hominids. So what? What is
> JW> the big deal, Paul?
> No one knows how bipedalism started in dinosaurs, birds or
> kangaroos. They were all probably quite small creatures at the
> time with much more favourable power/weight ratios enabling an
> enormous variety of highly plastic responses to innumerable
> changes in niche.

Another case of "special pleading", except in this instance,
Crowley is explaining-away the unexplained (for all bipeds
other than hominids), while showing a specio-centric bias
toward hominid bipedalism.
I notice, Paul, that you don't seem to want to hang out on What's the matter; non-human animal fossils
don't turn on that big imagination of yours?

>From the millions of species about the size
> of a shrew or a squirrel, a few found it more convenient to hop
> or use their upper limbs for other purposes, rather than run on
> all fours. Without specific data, no special explanation is
> appropriate.

"Appropriate"?? The crux of the problem is that, at least in the
case of the mammals (kangaroo rat and marsupial kangaroo), their
ancestors were land animals. In the case of dinosaurs, their
immediate ancestors were terrestrial archosaurians. Curious,
Paul, that the dinosaurs' cousins, the crocodilia, are aquatic
quadrupedal "sprawlers".
Nothing gets the legs straight under the center of gravity faster
than a terrestrial adaptation.

> The change from the LCA to the hominids is of an utterly
> different nature: there was a fairly large ape with an
> established method of locomotion,

Which was..... <?> (You are assuming we *know* what this
"established" type of locomotion explicitly was. We don't. Most
paleoanthopologists are now suggesting a brachiating primate as
the LCA).

>which it altered to become
> bipedal. It was a particular event at a particular time that
> calls for a particular explanation.

It isn't that particular, Paul. Your "particular" scenario
sounds so special and unique, if I blinked, I would think
you were using as a metaphore the Book of Genesis.

> JW> However, if the LCA had a
> JW> mosaic of bipedal and quadrupedal characteristics, there would
> JW> have been no deterioration.

Nearly all brachiator-type, fully-arboreal primates use FULL
bipedal locomotion when they (infrequently) find themselves on
the ground.

> These are empty words about a purely hypothetical animal.

You mean, like your "aquatic ape"? Talk about hypocrisy.