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.Īlthough 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 they 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. ![]() 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. 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.ĭial'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. As far as tree dwellers go, of the hundreds of nonavian gliding vertebrates around today, not one flaps its appendages. But both the arboreal and the cursorial scenarios have explanatory gaps. Feathers on their forelimbs enhanced lift, thereby allowing the creatures to take wing.Īs the idea that birds descended from dinosaurs gained acceptance by all but a few paleontologists, so too did the cursorial hypothesis. 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. 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. Traditionally, scholars have advanced two theories for how bird flight evolved. 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. Unfettered, however, the chick flapped its tiny wings while climbing and steadily made its way up. 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. These are, after all, the scientists who study Tyrannosaurus rex and other fearsome beasts of the past. Scientific American writer Kate Wong's report from that meeting, which originally ran in the January 2002 issue of the magazine, appears below.Ī new view of the origin of bird flight emergesīOZEMAN, MONT.-It's not often that a presentation given to the Society of Vertebrate Paleontology elicits coos and clucks of sympathy. ![]() Dial outlined his so-called wing-assisted incline running (WAIR) hypothesis in a presentation given to the Society of Vertebrate Paleontology in October 2001. So argues Kenneth Dial of the University of Montana in a paper published today in the journal Science. By flapping their front appendages, the animals gained more traction as they were running up steep inclines. Early birds may have used their wings not for flying, but for running.
0 Comments
Leave a Reply. |