The origin of feathers and the origin of flight have been a contentious chicken-and-egg issue in the scientific world for decades. Did feathers develop as a flight mechanism or were they first used for other purposes. Now, the discovery of an Archaeopteryx skeleton with feathered trousers bolsters the idea that these feathers weren’t for flying and initially may have been used as impressive displays.
The findings in the journal Nature shed light on the complex evolution of feathered flight. Archaeopteryx, which lived in the late Jurassic period roughly 150 million years ago, is considered a transitional species, sharing many characteristics of both dinosaurs and modern birds. The handful of skeletons and their fossilized feather impressions have led to various ideas about how this dinosaur lived. Some say its feathers were used for flight, others argue that their plumage was primarily for showing off to potential mates. Some saw feathers on the animals’ hind limbs and proposed that Archaeopteryx was a four-winged glider, using both pairs of limbs to soar through the air.
Paleontologists of Ludwig-Maximilians-Universitaet in Munich studying a new specimen of Archaeopteryx have found previously unknown features of the plumage, which shed light on the original function of feathers and their recruitment for flight. A century and a half after its discovery and a mere 150 million years or so since it took to the air, Archaeopteryx still has surprises in store: The eleventh specimen of the iconic basal bird so far discovered turns out to have the best preserved plumage of all, permitting detailed comparisons to be made with other feathered dinosaurs.
The fossil is being subjected to a thorough examination by a team led by Dr. Oliver Rauhut, a paleontologist in the Department of Earth and Environmental Sciences at LMU Munich, who is also affiliated with the Bavarian State Collection for Paleontology and Geology in Munich. The first results of their analysis of the plumage are reported in the latest issue of Nature. The new data make a significant contribution to the ongoing debate over the evolution of feathers and its relationship to avian flight. They also imply that the links between feather development and the origin of flight are probably much more complex than has been assumed up to now.
The new fossil also suggests that archaeopteryx, unlike its distant ancestor Microraptor which would glide the prehistoric skies several million years later, did not have two sets of wings. Why feathers were on its legs is another intriguing mystery to paleontologists like Rauhut. The currently proposed theory is that feathers evolved for a specific advantage besides flight. In modern ostriches, feathers provide balance and maneuverability, advantages that were already developed by the time that birds evolved the ability to fly. Leg feathers also offered a parachute advantage to break falls as the birds landed. In addition to advantages for movement it is also likely that the feathers had use in camouflage, sheltering newborn hatchlings, or may have been a product of sexual selection, with brightly colored feathers used to attract mates.
“For the first time, it has become possible to examine the detailed structure of the feathers on the body, the tail and, above all, on the legs,” says Oliver Rauhut. In the case of this new specimen, the feathers are, for the most part, preserved as impressions in the rock matrix.
So far 11 specimens of Archaeopteryx have been discovered, revealing further insight into this so-called “basal bird.”
Predatory dinosaurs, known as therapods, once had body plumage to provide thermal insulation. These dinosaurs actually predated Archaeopteryx. Their feathers were not used for flight but, instead, may have been used for camouflage, brooding and display. In contrast, the feathers of Archaeopteryx appear to have an aerodynamic form and were probably important in its aerial abilities.
By examining the new specimen, the researchers have been able to clarify the taxonomical relationship between archaeopteryx and other species of feathered dinosaur. The diversity in form and distribution of feather tracts is particularly striking. For example, among dinosaurs that had feathers on their legs, many had long feathers extending to their toes, while others had shorter down-like plumage. If the feathers evolved first for flight, there would have been more functional constraints that limited their range of variation.
“It is even possible that the ability to fly evolved more than once within the theropods,” said Rauhut. “Since the feathers were already present, different groups of predatory dinosaurs and their descendants, the birds, could have exploited these structures in different ways.”
The findings are published in the journal Nature.
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