Winter World_ The Ingenuity of Animal Survival - Bernd Heinrich [47]
In the 1990s, however, spectacular bird fossils, aged 124 to 147 million years, were uncovered from volcanic ash sediments in China’s Liaoning Province. These did not provide direct-line-of-decent type evidence, but they are providing new insights into the evolution of feathers (though not necessarily into the timing and branching points of various possible scenarios of dinosaur-bird relationships). One of the first Liaoning protobirds recovered, named Confuciornis, also had the same type of feathers as fully modern birds and it was even more closely related to modern birds than was Archaeopteryx. In 1996, however, the same deposits also yielded a small bipedal birdlike theropod dinosaur named Sinosauropteryx. Like its relative the Velociraptor dinosaur, Sinosauropteryx had sharp teeth, a long tail, and sharp claws. It was a predator with hind limbs built for fast running. Most significantly, though, the body of this nonbird had featherlike structures as shown by clear imprint in the fine-grained volcanic ash within which it was exquisitely preserved. Of special note: the feathers on the front limbs of this fossil were totally inadequate to support flight. That is, none of the feathers of this primitive protobird were likely used for flight. Sinosauropteryx (and other subsequently discovered dinosaurs with similar feathery structures) strongly suggests, therefore, that feathers for flight originated from insulation. The big question was and is: How can downy insulation evolve into flight feathers? I had not given this question much thought but one night in early March 2002, when I was at my cabin in the Maine woods and felt it shake in the wind and heard the pounding of the rain on the roof at night, an idea just popped up out of nowhere, and I present it here.
It had already been a warm winter—by Maine standards, and on the night in question, temperatures were only a degree or two above freezing. So instead of blizzarding, it was pouring rain. After a day of hiking in the woods, my boots had soaked up moisture, and I still had cold feet. My thoughts turned from my feet to Jack London’s story of the cheechako who died because of wet feet. The trite and obvious was suddenly steeped with meaning: The kinglet’s insulation can do wonders, but if that insulation is wetted then the bird might as well be naked for all of the good it does. That is why a blizzard and subzero temperatures are preferable to being subjected to a cold rain. Almost any rain is a cold, potentially lethal rain. Rain must be a severe test for a small endothermic bird in particular, because the fluffier (and generally the better) the insulation, the more it could act like a sponge to suck out the heat and the life. (Insects simply cool down, and insulation is then irrelevant.) Enduring and surviving wetness must have been a large selective pressure in the evolution of birds when they became continuously or nearly continuously endothermic. How did they evolve to meet this challenge? By the use of wing feathers? Is it a coincidence that survival of grouse chicks in Maine depends on rain-free weather in the time before they can fly?
Wing as “raincoat” to protect insulating down.
In a number of the flightless dinosaur fossils we can observe patches of featherlike structures on the arms and shoulders, and these feathers are more tightly organized into flat and regular patterns. They are attached to the posterior surface of the ulna, a bone in the arm, rather than over the rest of the body. However, these already modified feathers could not possibly have been used for flight, because they were only 5 to 7 centimeters long. Could they have served instead