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Feathered Dinosaur or Bird?
A New Look at the Hand of Archaeopteryx
ABSTRACT
A detailed examination of wrist and manus skeletons in Archaeopteryx,
and their comparison with those of modem birds, demonstrates
an overwhelmingly avian appearance, much more so than
has been previously recognized. Many workers have considered
feathers to be the only indisputable evidence for the avian identity
of this early bird. Although only a few skeletal characters have
been used to support its avian identity, we believe that this is due
to a lack of detail in previous analyses. We offer a list of eight
uniquely derived avian characters or character complexes in the
wrist and manus of Archaeopteryx. This further indicates that
Archaeopteryx is a bird, with wings used for flying rather than for
predation, and provides some fundamental skeletal differences
between the oldest birds and their immediate ancestors. We extend
our comparisons to the only other bird with Archaeopteryx-like
morphology in the manus, Confuciusornis, and show how the
wrist and manus may provide useful clues for discerning potentially
older and unknown birds in the future. In addition, the large
number of uniquely avian characters in the wrist and manus contrasts
with a more primitive anatomy in other parts, providing
another example of mosaic evolution, as the structure of the wing
modernized at a more rapid rate than other anatomical units.
Introduction
Since the discovery of Archaeopteryx in 1861, extensive
studies have been conducted on this genus, and the past two decades
marked a new era of study for Jurassic birds. One result
has been the resurrection, mainly by Ostrom in the 1970s, of
the theory of the dinosaur origin of birds. This hypothesis derives
most of its support from comparison between Archaeopteryx
and a few theropod dinosaurs, primarily Deinonychus.
Although strongly challenged by ornithologists and many pale-
Zhonghe Zhou and Larry D. Martin
Zhonghe Zhou, Institute of Vertebrate Paleontology and Paleoanthropology,
Chinese Academy of Sciences, P.O. Box 643, Beijing 100044,
China. Larry Martin, Natural History Museum and Department of
Ecology and Evolutionary Biology, University of Kansas, Lawrence,
Kansas 66045, United States.
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ornithologists, this theory has been broadly acclaimed among
vertebrate paleontologists. Ostrom even went farther, stating
that, were it not for the remarkable feather imprints, both of the
early Archaeopteryx specimens (London and Berlin) would
have been identified unquestionably as coelurosaurian theropods
(Ostrom, 1976). This argument has been echoed in an extensive
literature. Less attention has been paid to the significant
similarity between Archaeopteryx and modem birds apart from
the feathers and claws (Feduccia and Tordoff, 1979; Feduccia,
1993).
The wrist and manus bones in Archaeopteryx, when submitted
to detailed analysis and comparison with modem birds, illustrate
many avian skeletal characters that are important to the
flight of birds and that were subject to complex morphological
change in early avian evolution.
ACKNOWLEDGMENTS.—We thank Desui Miao for reading
the manuscript, and we benefited from discussion with Christopher
Bennett. We are grateful to Peter Wellnhofer, Burkhard
Stephan, Lawrence Witmer, and John Ostrom for their critical
reviews and valuable advice and suggestions. We also are indebted
to John Chorn for reading the abstract and preparing
some of the figures.
Character Analyses
A total of eight uniquely derived avian characters or character
complexes from the wrist and manus skeletons of Archaeopteryx
are recognized. We have been able to examine the originals
or good casts of all seven known specimens of
Archaeopteryx, especially the Berlin and Eichstatt specimens.
Ostrom listed several theropod dinosaurs as having the closest
wrist and manus structure to Archaeopteryx. Among the genera
most frequently used in comparisons are Deinonychus, Velociraptor,
Omitholestes, and Chirostenotes; therefore, our comparisons
will focus on the similarities between Archaeopteryx and
modem birds on one hand, and the difference between Archaeopteryx
and these dinosaurs on the other. The homologies of
the digits of birds and dinosaurs is still controversial among paleontologists
and embryologists (Hinchliffe, 1985; Martin,