In November 1859, Charles Darwin’s Origin of the Species by Means of Natural Selection was published. In 1862, a complete and delicately detailed fossil was discovered, not quite bird and not quite dinosaur. With splayed feathered wings, a bony tail, and tiny sharp teeth, its image is still iconic of evolution today: a halfway point between reptile and bird frozen in stone. It was dubbed Archaeopteryx lithographica, meaning “Ancient Wing.” However, just what Archaeopteryx really means for the study of evolution is still up for debate.
Advances in science and excavation of China’s rich fossil history has successively challenged Archaeopteryx’s relation to today’s birds, its ability to fly, and even its status as the first bird-like dinosaur.
The latter title might have been filched by Aurornis xui, a small feathered fossil discovered by a farmer in Liaoning Province, China, which might have lived as long as 160 million years ago, predating Archaeopteryx by 10 million years. The discovery of the slightly larger Microraptor zhaoianus, also recently discovered, has put a new spin on our understanding of the evolution of flight because it had four wings—a mode of transportation neglected by creatures alive today.
Part of the problem in placing Archaeopteryx on the evolutionary tree stems from the confusion over just what makes a bird a bird and a dinosaur and dinosaur. Is the difference feathers? Probably not. Paleontologists have unearthed more than 30 different species of feathered dinosaurs, leading some scientists, such as Oliver Rauhut of Ludwig Maximilian University in Munich, to propose that all dinosaurs might have grown some type of feathers. Is it the teeth? Again, probably not. Although no modern bird has true teeth, Archaeopteryx had a mouth full of them. Teeth and claws might well have been a common feature as the earliest birds finished the transition from reptiles.
Currently, scientists have grouped species such as Archaeopteryx and Aurornis, which seem to be closer to modern birds than to dinosaurs, under the name Avialae. However, the debate rages over just how close to birds Avialae were, and if the transition happened more than once.
Along these lines, the latest blow to the status of Archaeopteryx came at a presentation at the annual meeting of the Society of Vertebrate Paleontology, held in Los Angeles in November, by Michael Habib of the University of Southern California. He proposed that Archaeopteryx could have been in the process of losing its flight. Like the modern ostrich or penguin, Habib proposes that Archaeopteryx might have had ancestors that could fly, but then adapted to a lifestyle that did not require it any longer.
Habib calculated the fossil’s bone ratios and feather symmetry and found them surprisingly similar to modern flightless island birds. What’s more, Archaeopteryx lived on an archipelago, a geographic location that has limited the need for flight in some modern birds.
While it might seem that paleontology could be witnessing another stage in the fall of an idol, it is certain that whatever the role Archaeopteryx played in the evolution of birds, it has played an absolutely critical role in evolution of paleontology. The questions it poses will continue to advance our understanding of life and its evolution for generations to come.
Source: Kaplan, Matt (2013). Theory suggests iconic bird lost its flight. Nature News. doi:10.1038/nature.2013.14142
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