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302 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY
flexion. Ostrom's analysis also can be extended to address the
presence of the semilunate carpal, the precursor of the trochlea
carpalis, in Archaeopteryx; it too may have served for automatic
supination of the hand and metacarpus (Vazquez, 1992).
Such supination undoubtedly served to streamline the distal
portion of the wing during the upstroke, an action necessary to
reduce profile drag (Rayner, 1988b). Our experimental evidence
concerning the action of the supracoracoideus in powered
flight reveals this muscle's potential for increasing the
rate, and perhaps extent, of supination during upstroke. These
findings underscore the functional importance of a morphologically
derived supracoracoideus with a dorsally directed tendon
in modem birds. The implications of these findings have been
reported (Poore et al., 1997).
ACKNOWLEDGMENTS.—We gratefully acknowledge the assistance
of our good colleagues Peter Wellnhofer (Bayerische
Staatssammlung fur Palaontologie und historische Geologie,
Munich), Gunter Viohl (Jura-Museum, Willibaldsburg, Eichstatt),
Jose Sanz (Universidad Autonoma de Madrid), and Herman
Jaeger (Humboldt Museum fur Naturkunde, Berlin) for
providing access to the specimens in their charge and for all
their hospitality and generosity. In fond memory, we dedicated
this "exploration" to our dear colleague Herman, without
whom most of this would not have been possible. For technical
assistance with the experimental procedures, we thank Maki
Morimoto and Amie Valore. We thank Kathy Brown-Wing
(Brown University, Providence, Rhode Island) for preparation
of the illustrations used in Figures 3 and 4. This work was supported
in part by National Science Foundation grant IBN
9220097 to one of us (GEG).
Wrist Anatomy
THE MANIRAPTORAN WRIST
Important to this discussion of supination of the hand in
modern birds is a review of the evolution of the wrist in
maniraptoran theropods and Archaeopteryx. Unknown before
1964, the semilunate carpal of theropods was first reported in
1969 (Ostrom, 1969a), and a detailed, functional interpretation
followed a few months later (Ostrom, 1969b). That analysis
has apparently been accepted. It was shown therein that the
semilunate carpal element of Deinonychus (and later of Velociraptor
and other maniraptoran taxa) articulated in a tight,
rigid union with the first and second metacarpals distally. The
opposite proximal surface was a well-finished trochoidal articular
surface that permitted a high degree of flexion-extension
with the ulna (Figure 1). Because of its highly canted or pronounced
asymmetrical shape on the proximal surface, the semilunate
carpal also forced the metacarpus to supinate (circumduct)
up to 45° as the wrist was flexed. At the carpal joint,
supination must have been just as important as flexion because
the articular facet was well formed and highly finished in all of
the specimens in which it was found. That particular kind of
wrist motion was believed at the time (1969) to have been an
FIGURE 1.—Key components of a maniraptoran theropod (Deinonychus antirrhopus
Ostrom) forearm to illustrate hypothesized action imposed by the
semilunate carpal (key carpal) during flexion-extension: A, metacarpals I and II
and their relationship to the key carpal; B, the asymmetrical proximal ginglymus
of the key carpal causes supination (circumduction) of the closely
adjoined metacarpus through approximately 45°; c, surface aspects of the key
carpal: l=distal articular surface, 2=proximal articular surface, 3 = lateral surface.
(Modified from Ostrom, 1969b.)
important part of the predator action of Deinonychus, the first
taxon in which it had been found. Subsequently, when recognized
in other maniraptoran specimens {Velociraptor, Stenonychosaurus,
and Sinomithoides), it apparently was presumed to
have served a similar raptorial role related to the function of the
manus.
Although the biomechanical actions that were produced by
this particular wrist appear quite obvious, exactly what biological
role these movements played in maniraptoran life is not so