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Re: Homo amphibius and Hypothermia
Phillip Bigelow (n8010095@henson.cc.wwu.edu)
Wed, 28 Dec 1994 04:35:06 GMT
Troy Kelley <tkelley@hel4.brl.mil> writes:
>See if you can post a reference as to the weight of the average dolphin.
>My guess is that an average dolphin weights less than 500 pounds. I would
>guess, A LOT LESS. Probably about 250 pounds for a male. So how can a
>dolphin weighing less than 500 pounds possibly stay warm in the water??
>Troy Kelley
Actually, the average mass of a dolphin is 363 pounds, which is right
between my rough approximation and your approximation. My _point_ was:
There are no low-mass, hairless aquatic mammals that weigh as little
as a female A. afarensis. Four estuarian dolphins _may_ fall within the
uppermost weight estimate for a _male_ A. afarensis, but, keep in mind, that
is four species out of 76 species of whales _and_ dolphins (total).
The summaries that I could gather on mass are below:
1) Mass estimate of Lucy (A. afarensis): Female= 25 KG
Male= approx. 50 KG
(taken out of: Carroll, R.L. 1988. Vertebrate Paleontology and Evolution.
Freeman Press).
2) Total number of valid species of cetaceans (whales, dolphins, and
porpoises) in the world = 76 species. (Watson, 1981).
3) Average weight of all species of cetaceans = 5,790 KG (almost 6 tons).
(Watson, 1981).
4) Most massive is the Blue Whale, with a body mass of 80,000 KG (minimum
value), or 90 tons. (Watson, 1981).
5) The least massive are the La Plata River Dolphin, the Gulf Porpoise, and
the Estuarine Dolphin, with a mass of 36 KG, or 80 pounds, and the Finless
porpoise, with a mass of 30 KG, or 66 pounds. These four species are the
only hairless mammals in the world that are aquatic at less than 100
pounds. They therefore comprise 5% of all cetacean species. (Watson,
1981).
6) The average weight of all dolphin species is = 166 KG, or 363 pounds.
(I did the averaging; the reference is the same: Watson, 1981).
Because dolphins are the most numerous of the cetacean species,
the median weight for all cetaceans would therefore be higher than 363
pounds, although I didn't go through the statistics to find the exact
median weight.
7) There are no hairless semi-aquatic mammals in the world that have less mass
than the hippopotamus. I regret that I don't have a reference to back this claim
up, but I challenge anyone to come up with an example of a hairless
semi-aquatic mammal that weighs less than the hippo.
So, it seems from animals that are living today, that the _bottom_ mass
limit for hairless animals to survive in temperate to tropical water is
around 30 KG (66 pounds). There are no other hairless aquatic mammals
weighing less than this. These temperate/tropical water porpoises have 20%
body fat as insulation (minimum) (Watson, 1981).
Healthy modern adult humans have body fat that is roughly half of this
value (Grays Anatomy, 1974). We have no way of knowing if A. afarensis was
hairless, or if the species was obese, because hair and fat are not preserved
as fossils. If Lucy's "aquatic" ancestor had 10% body fat, it is doubtful
that it would be enough to fully insulate the species from hypothermia as a
result of it's small mass (25-50 KG, or less), since the smallest tropical
dolphins have at least 20% body fat. Furthermore, female A. afarensis
individuals have been estimated to have weighed only 25 KG (by D.J. Johanson),
which is 17% less massive than the smallest hairless aquatic animal alive
today (the Finless Porpoise). If the "aquatic" female ancestor to A.
afarensis also weighed around 25 KG, does that mean that the female of the
species was terrestrial, while the male (at around 50 KG) was aquatic?
That is doubtful.
Another problem that Morgan and her Aquatic Ape supporters _constantly_
ignore is the _reason_ why dolphins are hairless. It is not simply because
they are aquatic; rather, it is because hairlessness reduces drag in the
water during high-speed swimming. If the ancestor of humans was
"semi-aquatic" (as many of the proponents claim), there is no evolutionary
need to loose insulating hair, because "semi-aquaticness" doesn't involve
high-speed swimming. If all these creatures did was wade around the
shoreline, a hairless, low-drag body would be a useless evolutionary
adaptation.
Yet another problem with the Aquatic Ape Hypothesis is that the young (the
new-borns and the children) would be even smaller than the adults. In
whales and dolphins, calves that are newly-born are already 45% of their
mother's length, and are over 18% of their mother's weight (Watson, 1981).
In humans, an 8 lb. new-born is only 6% of the mass of its mother (assuming
a 130 lb mother, which is pretty typical). In order to compensate for their
small mass, cetacean babies are fed an _extremely_ rich diet of milk, which
is many times more fattening than human milk. This diet keeps the core
temperature of dolphin calves high, until the calves get large enough to
maintain heat by mass homeothermy (endothermic gigantothermy). (For a quick
summary of what endothermy, ectothermy, mass homeothermy, gigantothermy
mean, read John Horner's book _Digging Dinosaurs_. It has an excellent
introdutory lesson in these concepts).
In my opinion, there are absolutely _no_ similarities between humans and
dolphins, as far as aquatic adaptation is concerned. I still think the
small "aquatic apes" would spend all of their time trying to keep warm.
(Remember, water takes heat away from the body more than 20 times faster
than air does (Watson, 1981, page 22)), and the smaller an animal is, the
worse it gets.
For anybody who is interested, my references are included below:
Carroll, R.L. 1988. Vertebrate Paleontology and Evolution.
Freeman Press.
Watson, L. 1981. Sea Guide to Whales of the World. E. P. Dutton,
New York. 302 pages.
Grays Anatomy. 1974.
Horner, J. 1989. Digging Dinosaurs. Workman Press.
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