Palaeontology

Archaeopteryx plumage: First show off, then take off

LMU paleontologists are currently studying a new specimen of Archaeopteryx, revealing previously unknown features of the plumage. The findings unveil information on the original function of feathers and their recruitment for flight.

150 years after discovery and a mere 150 million years since it took flight, Archaeopteryx still has hidden mysteries that need solving: The eleventh specimen of the iconic “basal bird” turns out to have been the best preserved plumage thus far, allowing detailed comparisons to be made with other feathered dinosaurs. The fossil is still undergoing extensive examinations by a team led by Dr. Oliver Rauhut, a paleontologist in the Department of Earth and Environmental sciences at LMU Munich, who is also associated with the Bavarian State Collection for Paleontology and Geology in Munich. The primary results of their analysis of the plumage are reported in the latest issue of the journal Nature. This new information makes a major contribution to the ongoing debate over the evolution of feathers and its relation to avian flight. The data also implies that the connections between feather development and the origin of flight are potentially much more complex than what was previously thought.

“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. “Comparisons with other feathered predatory dinosaurs indicate that the plumage in the different regions of the body varied widely between these species. That suggests that primordial feathers did not evolve in connection with flight-related roles, but originated in other functional contexts,” says Dr. Christian Forth of LMU and the Bavarian State Collection for Paleontology and Geology in Munich, first author on the new paper.

Feathered Wing Fossil: LMU Munich
Feathered Wing Fossil: LMU Munich

To keep warm and to catch the eye

It has now been discovered that predatory dinosaurs (theropods) with body plumage predate Archaeopteryx and their feathers probably provided thermal insulation. Advanced species of predatory dinosaurs and primitive birds with feathered forelimbs potentially used them as balance organs when running, much like ostriches do today. Furthermore, feathers may have served as useful functions in brooding, camouflage and display. The feathers on the tail, wings and hand-limbs would have probably fulfilled functions in display, but it is very unlikely that Archaeopteryx were capable of flight. “Interestingly, the lateral feathers in the tail of Archaeopteryx had an aerodynamic form, and most probably played an important role in its aerial abilities,” says Foth.

In terms of their investigation of the plumage of the new fossil, the research team has been able to identify the taxonomical relationship between Archaeopteryx and other species of feathered dinosaur. The diversity in form and distribution of the feather tracts is particularly striking. For instance, among dinosaurs that had feathers on their legs, many had long feathers that extended as far as their toes, while others had shorter down-like plumage. “If feathers had evolved originally for flight, functional constraints should have restricted their range of variation. And in primitive birds we do see less variation in wing feathers than in those on the hind-limbs or the tail,” explains Foth.

     

The findings suggest that feathers obtained their aerodynamic functions secondarily: Once feathers had been invented, they could be co-opted for flight. It is even possible that the ability to fly evolved more than once within the theropods,” says 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 new discovery also contradicts with the theory that powered avian flight evolved from earlier four-winged species that had the ability to glide.

A cultural treasure

Archaeopteryx represents a transitional form between reptiles and birds and is the possibly both the earliest and best-known bird fossil. It is concrete evidence that modern birds are direct descendents of predatory dinosaurs, and thus are themselves modern-day dinosaurs. The many new fossil species of feathered dinosaurs discovered in China in recent years have made it possible to place Archaeopteryx within a larger evolutionary context. Yet, when feathers first appeared and the frequencies of flight are aspects that are still undetermined.

The eleventh known specimen of Archaeopteryx is still held privately. Like all the other examples of the genus, it was discovered in the Altmuhl valley in Bavaria, which in the Late Jurassic times was located in the northern tropics, and at the bottom of a shallow sea, as all Archaeopteryx fossils found so far have been recovered from limestone deposits. The collector was not only willing to make the specimen available for study, he also had it registered on the list of protected German Cultural Treasures to ensure that it would remain accessible to science. This is a very good example of successful cooperation between private collectors and academic paleontologists,” says Rauhut. The detailed analysis of the fossil was made possible by the financial support provided by the Volkswagen Foundation.

 

Contributing Source: LMU Munich

Header Image Source: LMU Munich

 

     

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