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308 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY
Rao (1992), the critical region of Sinornis is not preserved, so
we have no evidence. Zhou and Zhang (1992) did not note either
feature in any of the material of Cathayornis, and the specimens
of Iberomesornis (Sanz et al., 1988; Sanz and Bonaparte,
1992) and Concornis (Sanz et al., 1988; Sanz et al., 1995) do
not show them either (confirmed by JHO). The precise stratigraphic
source of the newly reported Confuciusomis is in
doubt, but Hou (1995; see also Hou et al., 1995) made no mention
of either feature.
EARLY STAGES OF FLIGHT
Sy (1936) described humeral axial rotation as a mechanism
for the execution of wing upstroke and downstroke in pigeons
and generalized its importance for other relatively small birds
possessing powered flight. His observations that pigeons with
bilateral tenotomy of the supracoracoideus are capable of
flight, but cannot take off from the ground, are often cited in
discussions of the evolution of powered flight (Olson and Feduccia,
1979; Ostrom, 1976b; Ruben, 1991). Perhaps less appreciated
was Sy's (1936) identical procedure on at least one
adult crow, for which he reported not only normal takeoff but
normal flight. Sokoloff et al. (1994), in a cinematographic/
electromyographic analysis of adult starlings, bilaterally denervated
{n—4) or tenotomized («=2) the supracoracoideus and reported
that all birds but one could take off, but not without difficulty.
Of particular importance are their observations that
takeoff and flight in these deprived birds is not normal. In our
estimation, the extent of impairment incurred by loss of the supracoracoideus
for different species is a function of wing loading
(body weight/wing area), the mechanical organization of
the supracoracoideus, or some combination thereof. We believe
the impaired takeoff capability of birds deprived of a
functional supracoracoideus relates to their inability to rapidly
rotate the humems on its axis.
Biewener, A.A., K.P. Dial, and G.E. Goslow, Jr.
1992. Pectoralis Muscle Force and Power Output during Flight in the Starling.
Journal of Experimental Biology, 164:1-18.
Bock, W.J., and P. Buhler
1995. Origin of Birds: Feathers, Flight and Homoiothermy (Ursprung der
Vogel: Feder, Flug und Homoiothermie). Archaeopteryx, 12:5-13.
Brown, R.HJ.
1951. Flapping Flight. Ibis, 93:333-359.
Dial, K.P, and A.A. Biewener
1993. Pectoralis Muscle Force and Power Output during Different Modes
of Flight in Pigeons. Journal of Experimental Biology, 176:31-54.
Dial, K.P, G.E. Goslow, Jr., and F.A. Jenkins, Jr.
1991. The Functional Anatomy of the Shoulder in the European Starling
(Sturnus vulgaris). Journal of Morphology, 207:327-344.
Dial, K.P, S.R. Kaplan, G.E. Goslow, Jr., and F.A. Jenkins, Jr.
1988. A Functional Analysis of the Primary Upstroke and Downstroke
Literature Cited
The earliest unequivocal evidence pertaining to bird flight is
that of Archaeopteryx. There is no debate concerning its stratigraphic
age. There is no question about its avian affinities. The
famed feather impressions on most of the seven specimens establish
that if Archaeopteryx flew, a feathered airfoil was available.
The apparent presence of an ossified sternum in the most
recently found specimen suggests that a skeletal origin for the
pectoralis (and supracoracoideus?) existed in at least some of
the specimens, as is also suggested by the pronounced deltoid
crest on the humems for insertion of the pectoralis. The supracoracoideus
of Archaeopteryx was not diverted to a dorsal insertion,
however, and thus could neither rapidly rotate the humerus
nor augment supination of the distal wing.
Conclusions
In summary, Archaeopteryx was apparently incapable of the
high-velocity rotation of the humems about its longitudinal
axis that would have been generated by a derived supracoracoideus
with a dorsally inserting tendon. The subsequent evolution
in later forms of an acrocoracoid, dorsally inserting tendon,
and tuberculum dorsale resulted in (1) rotation of the
humerus on its longitudinal axis to position the forearm and
hand so their extension orients the fully outstretched wing in
the parasagittal plane (i.e., the wing's ventral surface faces laterally,
the position appropriate for the beginning of the subsequent
downstroke), (2) increased speed of the upstroke, and (3)
augmented supination of the hand to reduce drag. By relocating
the site of insertion of the supracoracoideus to an elevated position
on the dorsal surface of the humems (the novel external tuberosity),
wing supination was accelerated, and the range of
movement perhaps increased. Such augmentation of supination
and an increase in the velocity of upstroke must have provided
high selective value, particularly for rapid takeoff and landing.
Muscles in the Domestic Pigeon (Columba livia) during Flight.
Journal of Experimental Biology, 134:1-16.
Dodson, P.
1985. International Archaeopteryx Conference. Journal of Vertebrate Paleontology,
5:177-179.
Gauthier, J.A., and K. Padian
1985. Phylogenetic, Functional, and Aerodynamic Analysis of the Origin
of Birds and Their Flight. In M.K. Hecht, J.H. Ostrom, G. Viohl,
and P. Wellnhofer, editors, The Beginnings of Birds, pages
185-197. Eichstatt: Freunde des Jura-Museums, Eichstatt.
1989. The Origin of Birds and the Evolution of Flight. In K. Padian and
D.J. Chure, editors, The Age of Dinosaurs. Short Courses in Paleontology,
2:121-133. Knoxville, Tennessee: The Paleontological
Society.
Hecht, M.K., J.H. Ostrom, G. Viohl, and P. Wellnhofer, editors
1985. The Beginnings of Birds. 382 pages. Eichstatt: Freunde des