Re: Common Ancestor?
- From: alas_my_loves@xxxxxxxxx
- Date: Tue, 30 May 2006 21:42:03 -0400 (EDT)
The scientist-anatomist was Etienne Geoffroy Saint-Hilaire 1772-1844
The book (recently published) had illustrations and some narration.
When I realized that the backfloating in sea otters and humans seemed
somewhat unique, I remembered about the upside-down crabs. Other than
sloths, I can't think any other tetrapod that adopts a (horizontal)
spine down position habitually, though seals and monkeys do so at
times. This might mean that the LCA (extremely simple tubular
crayfish-like animal) split into 2 habitats, one favoring crawling on
sea floor (with spinal nerves ventral), the other swimming "backwards
upside down" (with spinal nerves dorsal). Something interesting is that
in humans and sea otters, while backfloating, suction feeding and
backstroking on water surface, the primitive arthropod condition
(spinal nerves downward) is experienced secondarily. Although mammals
have evolved significantly away from crabs, these 2 distinct examples
of mammals readopting this posture habitually shows parallel
convergence. That humans can, while on their backs (spine down), swim
forwards or backward with ease, and yet can also wade and walk
bipedally and also knee-crawl on mudflats (spine up) forwards or
backwards with ease (even laterally) shows ancient
omni-ambidexterosity in locomotion among our ancestors. (sorry if
I've drifted OT, the convergence sparked my interest) DD
.
- References:
- Common Ancestor?
- From: kramer . newsreader
- Common Ancestor?
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