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Aquatic Apes and Aquatic Dinos

Er, my two cents on a couple things. I agree that the idea of apes trying to touch the bottom of rivers and ponds while walking and that "made" upright humans is pretty goofy sounding. However, that was not how I was lead to understand the Aquatic Ape Theory (henceforth AAT). Also, this leads into dinosaurs, so I am really trying to stay on dino topic here, promise!!!

This information is from Desmond Morris's Book "The Human Animal." In that book, Morris argues a couple of interesting points: the vertebral column of Homo sapiens is the most flexible in the dorso/ventral plane than that of all other primates; we have noses that, while swimming head forwards, prevent water from entering (unlike the "pug" noses of other primates); we can hold our breath the longest; our heart rate slows, like an aquatic mammal, when diving (all other primates actually have heart rates that speed up when submerged -- a bad trait for diving/holding one's breath); we have the most copious urine and moist feces of any other primates; we have body hairs with a singular direction of travel; the loose skin between our fingers is not noted among other primates; we have the most body fat of all primates. I am not a diehard adherent of the theory, but I felt Morris brought up some interesting points. Those interested should read the book -- I felt it was very interesting and posed some questions for the terrestrial human evolution hypotheses. Just thought I'd note this stuff -- felt like there was too much of a straw man being made out of it. AAT surely doesn't explain everything, but it is intriguing nonetheless.

Which brings me to aquatic dinosaurs. Wish we had as much info on dinosaurs as we do primates but alas we do not. It would seem to me that evolving a bipedal stance from a quadrupedal tetrapod, while an intriguing alternative, would need quite a bit of physical evidence. For instance, you only get the laterally facing glenoid (the shoulder socket faces out) in the Maniraptorans and other advanced dinos leading to birds. Early theropods have none of these adaptations to allow the arm to operate like a bird arm, so the decoupling thing doesn't seem to work in an aquatic environment.

Why not have a really thick proximal tail, like in 'gators and crocs which swim with their tails in the water? Instead, the tails are long and appear to have served a useful function as a cantilever to balance the bipedal body in theropods. A back which is neither very flexible dorsoventrally or lateromedially also suggests that these early theropods were not very well adapted to an aquatic environment.

Alligators and crocs have a nose and eyes situated toward the top of their skulls, and their skulls have become flattened. One doesn't see this in theropods. Also, reduction of integument appears to be a trend in all secondarily aquatic verts -- reduced hair on mammals, and birds with thinner, more fusiform body feathers. This woud seem to argue against a feathered body forming in relation to an aquatic environment.

I know we're not suggesting theropods became entirely aquatic (are we?) but some relics of a past aquatic existence should be expected to show up skeletally. Bipedality by itself is not an example either for or against an arboreal or aquatic beginning for dinos and/or birds. All things being equal, I come down on the side of a relatively terrestrial beginning to birds from dinosaurs. I do not pretend to know the mechanisms by which this happened, but since there are so many terrestrial adaptations in dino skeletons and their ancestors, this seems to be the most parsimonious explanation.

Matt Bonnan

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