Our subject here is the leatherback turtle. Weighing up to 1600 pounds, it is the largest of the sea turtles. It is also the fastest turtle, hitting 9 miles per hour at times. But weight and speed are not necessarily mysterious; here are some characteristics that are:
The leatherback is the only turtle without a rigid shell. Why? Perhaps it needs a flexible shell for its very deep dives. What looks like a shell is its thick, leathery carapace -- a strange streamlined structure with five to seven odd "keels" running lengthwise.
These turtles are warm-blooded, and able to maintain their temperatures as much as 10°F above the ambient water, just as the dinosaurs apparently could.
The bones of the leatherback are more like those of the marine mammals (dolphins and whales) than the reptiles. "No one seems to understand the evolutionary implications of this."
Leatherbacks dive as deep as 3000 feet which is strange because they seem to subside almost exclusively on jellyfish, most of which are surface feeders.
Like all turtles, leatherbacks can stay submerged for up to 48 hours. Just how they do this is unexplained.
Their brains are miniscule. A 60-pound turtle possessed a brain weighing only 4 grams -- a rat's weighs 8!
Leatherbacks' intestines contain waxy balls, recalling the ambergris found in the intestines of sperm whales.
The stomachs of leatherbacks seem to contain nothing but jellyfish, which are 97% water. Biologists wonder how the huge, far-ranging leatherback can find enough jellyfish to sustain itself.
(McClintock, Jack; "Deep-Diving, WarmBlooded Turtle," Sea Frontiers, 37:8, February 1991.)