Posted on 01/10/2002 10:11:55 AM PST by Junior
BOZEMAN, MONT. -- It's not often that a presentation given to the Society of Vertebrate Paleontology elicits coos and clucks of sympathy. These are, after all, the scientists who study Tyrannosaurus rex and other fearsome beasts of the past. But that's exactly the reaction Kenneth Dial got when, at the group's annual meeting last October, he showed video footage of a fuzzy little partridge chick with its wings taped to its sides trying to climb a tree -- only to tumble down into Dial's waiting hands. Unfettered, however, the chick flapped its tiny wings while climbing and steadily made its way up. After teasing the audience for its sentimental display, the University of Montana biologist returned to the matter at hand: explaining how this and other experiments involving ground-dwelling birds led him to hatch a new hypothesis regarding the origin of avian flight.
Traditionally, scholars have advanced two theories for how bird flight evolved. One of these, dubbed the arboreal model, holds that it developed in a tree-dwelling ancestor that was built for gliding but started flapping to extend its air time. The other, known as the cursorial theory, posits that flight arose in small, bipedal terrestrial theropod dinosaurs that sped along the ground with arms outstretched and leaped into the air while pursuing prey or evading predators. Feathers on their forelimbs enhanced lift, thereby allowing the creatures to take wing.
As the idea that birds descended from dinosaurs gained acceptance by all but a few paleontologists, so too did the cursorial hypothesis. But both the arboreal and cursorial scenarios have explanatory gaps. As far as tree dwellers go, of the hundreds of nonavian gliding vertebrates around today, not one flaps its appendages. And why would natural selection have favored the development of little protowings in a theropod equipped with heavily muscled legs for running across the ground? Neither theory, Dial asserts, adequately addresses the step-by-step adaptations that led to fully developed flight mechanics.
Dial's eureka moment came after learning that partridges and their fellow ground birds routinely abandon terra firma in favor of trees and other elevated spots for safety. Although these animals appear to fly up into trees, he found on closer inspection that in many cases they were actually running up -- legs bent and body pitched toward the tree -- while flapping their wings. Subsequent research revealed that wing flapping assists in this vertical running by sticking the bird to the side of the tree, much as a spoiler helps to press a race car to a track.
Although the adult ground birds are generally perfectly capable of flying up trees, their preference for running may stem from a time early in life when the couldn't yet fly: before a baby ground bird has the ability to launch itself into the air, the only means it has for getting off the ground is vertical running. And as Dial's experiments show, when a juvenile is trying to evade a predator this way, the aid of even a partially formed wing can mean the difference between life and death.
Perhaps a bird ancestor's protowing conferred the same benefit, he suggests, and therefore natural selection favored its development. Over time, wings evolved to the point of enabling not only vertical running but, when employed by an animal running across the ground, flight.
So far Dial's model has ruffled few feathers. Living animals do not necessarily make good models of extinct ones, however. "Is that the way bird ancestors did it? Well, maybe, maybe not," comments Kevin Padian of the University of California at Berkeley. "But [Dial] is showing that it's possible." For his part, Dial is leaving it to the paleontologists to figure out whether his theory of the genesis of avian flight jibes with future fossil finds -- or whether it's for the birds.
Fundamendalism-creationism, topsoil, stratosphere, underarm, dental floss.
I'd have to add to all that the hypothesis presented here does not make much sense. If wings were evlved to help a critter run up a tree in acting like spoilers, they would change so as to continually get better at holding the creature onto the tree, not allowing them to fly up in the opposite direction.
Don't have time to argue this thread today though. A pity, it'd be delicious.
I would hope that not even diehards like my esteemed sparring partners Vade and Junior would give this idea much credence. I realize that discrediting this idea is not the same thing as discrediting the evolution of birds. Still, if evolution is true, if all of those alleged 'transitionals' check out, then it had to happen SOME way. And all ways proposed to date seem very unlikely, as Medved notes.
I had forgotten that phrase would include bugs.
I don't poo-poo evolutionary ideas automatically since I think quite a bit of adaptability was built into the prototypes of each family introduced into the biosphere. If bird wings evolved, I thought the 'started as stabilizers used while they lept after hopping insects' was the least absurd hypothesis. That does not explain the origin of feathers themselves though. They seem to spring up with the hook and barbule system already in place- except for fossils with down feathers which birds have today. How did the small biped dinos know they were going to need flight feathers?
That is a minor problem compared to proposing intermediates between the bird's continuous-throughput respiritory system and the in-out system of all other vertabrates.
Wouldn't you agree that this is an unlikely scenario, and for the exact reason I mentioned?
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