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290
1991). In this paper we use a "1, 2, 3" numbering of the digits
in birds, but we have no objection to the "2, 3, 4" identification
of embryologists. If the latter scheme is accepted, almost all
comparison with dinosaurs disappears. These characters are as
follows.
1. The semilunate carpal (Figure 1) is centered on the second
metacarpal (see Martin, 1991). In modern birds, this is
known to be a single distal carpal (II or III). A similar bone,
supposedly homologous to the semilunate carpal in Archaeopteryx,
is found in Deinonychus, Sinomithoides, and Velociraptor
(Ostrom, 1995). In Archaeopteryx (Wellnhofer, 1974), the
semilunate carpal is in contact with the first and second metacarpals,
but the articulating surface of the second metacarpal is
about 2.5 times as long as that of the first one. In contrast, in
Deinonychus, Sinomithoides, and Velociraptor the semilunate
carpal is articulated almost equally with each of the first two
metacarpals. From embryological evidence (Holmgren, 1955),
it is known that the semilunate carpal is centered on the second
metacarpal in modem birds and that this is clearly an advanced
avian character.
2. The third metacarpal slants ventrally toward the distal end
as in modem birds (Figure 2), as clearly revealed in the Eich-
B
c D
FIGURE 1.—Comparisons of the articulation between the semilunate carpal
(black) and the metacarpals: A, Velociraptor mongoliensis Osborn (modified
from Ostrom, 1976); B, Deinonychus antirrhopus Ostrom (modified from
Ostrom, 1976); C, Archaeopteryx (modified from Wellnhofer, 1974); D, a 19day-old
Struthio camelus Linnaeus (modified from Holmgren, 1955). Drawings
not to scale. (sl=semilunate carpal, 1 =metacarpal I, 2=metacarpal II.
A
SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY
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FIGURE 2.—Comparisons of the carpometacarpus: A, Archaeopteryx (cast of
Berlin specimen in the Natural History Museum of the University of Kansas)
in dorsal and slightly posterior view; B, a modern bird, Bubo virginianus
(Gmelin), in posterior view to show the similarly ventrally slanting profile of
metacarpal III toward the distal end. (2=metacarpal II, 3=metacarpal III.)
start and Berlin specimens of Archaeopteryx. The phalanges of
the outer digit also are lower and flatter than those of the middle
digit. As a result of this, the Eichstatt, Berlin, and Solnhofen
specimens show the third digit (as preserved) crossed by
the second digit. This relationship exists in part because the
shafts of the feathers ride over the outer phalanges and insert in
a fold of skin that forms the edge of the fleshy portion of the
wing. The manus of birds is bound together in the postpatagial
skin that bears the flight feathers. An impression of the postpatagium
appears to be present on the Berlin specimen and is indicated
in Heilmann's restoration of the wing (Heilmann, 1926,
fig. 21). It is not clear whether his restoration of the patagium
was based on the specimen or was inferred from modem birds.
The fact that the feathers extend onto the digit and are enclosed
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