Archaeopteryx: A flying reptile?
I’m intrigued by the Archaeopteryx, a fossil that is mentioned in many science textbooks. Was it a bird or a reptile? Do its features and its location in the fossil record support the evolutionary hypothesis or the creationist perspective?
Ever since it was discovered in 1861, Archaeopteryx lithographica (see photo) has been a controversial fossil. Its remarkable finding has provided certain credibility to Darwin’s theory of evolution. Archaeopteryx has a mixture of characteristics found in birds, reptiles, and theropod dinosaurs, and for that reason, scientists are divided regarding its origin, flight capacity, and position in the alleged evolutionary sequence from reptiles to birds. The ornithologists consider it as an arboreal bird with unusual traits and numerous reptilian characteristics, but reject the claim that it descended from dinosaurs. On the other hand, most paleontologists see Archaeopteryx as an intermediate link in the evolution of theropod dinosaurs to modern birds. For them, Archaeopteryx is a winged dinosaur that lived on the ground. Obviously, this conclusion assumes that dinosaurs were the ancestors of birds.
Archaeopteryx has several avian characteristics: the presence of a furcula (fused clavicles), the anatomy of the fingers and pubis, the existence of hollow bones, and the presence of feathers that appear modern. A recent study of the skull of one Archaeopteryx specimen, using high-resolution computerized tomography, has revealed that the brain of Archaeopteryx had lobes like the brain of a modern bird. However, similar results have been found in pterosaurs (flying reptiles) using the same technique. Therefore, this evidence does not conclusively support the avian nature of Archaeopteryx since pterosaur dinosaurs also have this characteristic. The recent discovery of hollow bones in Archaeopteryx is not a definitive evidence for active flight either, because some birds of the family Bucerotidae (e. g., ground hornbill) have very great hollows in their bones and, nevertheless, are poor flyers.
J. H. Ostrom* and other paleontologists suggest that the similarity between Archaeopteryx and theropod dinosaurs is much greater than the similarity between Archaeopteryx and birds. Therefore, Archaeopteryx would be a flying dinosaur with feathers. In fact, one of the seven well-known specimens was initially identified as a pterosaur, while other two specimens were identified as Compsognathus (a theropod dinosaur). This misidentification was not caused by bad descriptive work; the problem is that Archaeopteryx without feathers—or with feathers that have yet not been observed—looks extraordinarily like Compsognathus. This is the reason why certain paleontologists do not consider Archaeopteryx as a bird, but as a feathered dinosaur. Some say that the problem in determining the relationship of Archaeopteryx resides in the examiner’s perspective when examining the fossil.
Paleontologists also debate whether Archaeopteryx was able to fly and whether it was terrestrial or arboreal. Studies on several anatomical characteristics of Archaeopteryx—including feather symmetry, wing anatomy, and inferred muscular mass—have led to contradictory conclusions. Nevertheless, most experts maintain that the possession of feathered wings is a convincing argument in support of the capacity to fly. Published studies show that the same set of characters can be interpreted in two contradictory ways, resulting in very different models for the habits of an Archaeopteryx.
We must recognize that though Archaeopteryx has a mosaic of reptilian and avian characteristics, its well-developed wings and feathers of modern appearance would have required an enormous evolutionary change that has not yet been satisfactorily explained. This gap exposes a number of challenges to the proposed evolutionary scenario. What was there between Archaeopteryx and its predecessors without wings and feathers? No specimens have been found to illustrate such an evolutionary jump. Not only do we need to provide models for the evolution of feathers, but also for the rise of structures, organs, and physiology that would make possible their effective use. The development of flight ability by primitive reptiles would require the acquisition of very complex physiological and anatomical adaptations, including the capacity to keep the body temperature constant (endothermic; reptiles are exothermic), a high rate of metabolism (reptiles have a low metabolic rate), and loss of adaptations and organs that were already fully useful and optimized in the ancestors. Feathers must have co-evolved with the structures that control them and make them work. It is not simply the appearance of a cover of plumage, but also a set of characteristics that contribute to the operation of a very sophisticated structure.
One wonders why Archaeopteryx (and any other alleged ancestor of the birds) would have had wings or precursors of wings during millions of years if these organs were not fully functional. According to Darwinian theory, only the best fitted survive, and structures that are not an advantage to the species disappear. The question is, then, why evolution would have maintained a structure for million years until it became fully operative? If that happened, then we could believe that evolution has the capacity of predicting the future needs of a species, which implies supernatural powers. And if the structures were indeed fully functional, why should natural selection “improve” or change structures that already work suitably? The validity of natural selection as the motor of evolution is thus in question. In this sense, Archaeopteryx does not help solve the mystery of how flight came about in evolutionary terms, what their precursors were, or when such an evolutionary jump could have happened.
Archaeopteryx has been an enigma since it was discovered, owing to its puzzling combination of characteristics, many of which are common in some theropod dinosaurs; others are reptilian, while some others are specific to birds. What is more remarkable is the presence of modern feathers on what seems to be the body of a theropod. It is no surprise that ornithologists and paleontologists do not agree about the nature of this animal.
I believe that Archaeopteryx was a unique creature with characteristics that perhaps cannot be catalogued within any present category of living beings. Its origin and nature seem obscure, and, is possible that it is just one more example of the enormous creative capacity of the Creator.
Raúl Esperante (Ph.D., Loma Linda University) is a paleontologist at the Geoscience Research Institute in Loma Linda, California, U.S.A. His email address: firstname.lastname@example.org.
For a fuller treatment of this topic, check his article “¿Qué es Archaeopteryx?” in Ciencia de los Orígenes 68 (2004), and also Timothy Standish, “Fossil birds,” in Geoscience Reports 87 (2004). These articles can be found at http://www.grisda.org.
* J. H. Ostrom, “Archaeopteryx and the origin of birds,” Biological Journal of the Linnean Society 8 (1976): 91-182.