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NUMBER 89 291
in the skin of the patagium makes it impossible for the manus
to actually grip objects or act as a prey-capture mechanism.
The proximal portion of the third metacarpal is markedly anteroposteriorly
compressed and is tightly attached to the posterior
side of the second metacarpal. This character is obviously
present in modem birds but is absent in Deinonychus.
3. Four carpals are present in an avian arrangement (Martin,
1991). In the Berlin specimen (de Beer, 1954), there are four
preserved carpals, and they are even better displayed in the
Eichstatt specimen (Wellnhofer, 1974). Two of them are the
ulnare and radiale, which serve to connect the manus with the
forearm (Fisher, 1957), and the third (and largest) is the semilunate
carpal. The fourth carpal is relatively small and fuses to
metacarpal III (IV?) in later birds (Figure 3). No dinosaurs
have been described with these four carpals in an avian arrangement.
The semilunate has a proximal articulating facet for
the ulna on the ulnare. The Eichstatt ulnare is better preserved
and exposed than in the other specimens. Its tight articulation
with a semicircular external condyle on the ulna facilitates the
stabilization of the distal portion of the wing. In addition, the
third metacarpal does not extend as far proximally as the other
two. In Archaeopteryx, proximal to the third metacarpal, there
is a small carpal ("x-bone" of Hinchliffe (1985)) that in modem
birds fuses with the semilunate carpal to form the proximal end
of the carpometacarpus (Figure 3).
LU
FIGURE 3.—Comparisons of the wrist pattern: A, Archaeopteryx (a reconstruction
based on Wellnhofer, 1974); B, a modem bird, Gallus gallus (Linnaeus)
(modified from Hogg, 1980). Drawings not to scale. (r=radius, rd=radiale, sl=
semilunate carpal, u=ulna, ul = ulnare, x="x-bone" of Hinchliffe (1985), 1 =
metacarpal I, 2=metacarpal II, 3=metacarpal III.)
4. The distal metacarpals are simplified. The articulations
between the metacarpals and the phalanges are as in modem
birds and are different from dinosaurs. The distal end of the
first metacarpal is markedly narrower than the proximal end,
and the contact between the first and second metacarpals is
straight and tightly appressed along its length. Modem birds all
B
have a fused carpometacarpus, and this fusion is clearly a derived
character for birds. The first and second metacarpals diverge
distally in Deinonychus (Ostrom, 1976).
5. The second metacarpal is more robust than the other two.
This character in Archaeopteryx is related to the support of the
feathers provided by this element. In Deinonychus, Sinomithoides,
and Velociraptor the first metacarpal is, on the contrary,
more robust than the second one, indicating a totally different
adaptation for the hand. The second digit in
Archaeopteryx also is more robust than the other two (Wellnhofer,
1988). In Deinonychus and Oviraptor the first digit is
more robust than the second one. The first digit of Archaeopteryx
is proportionally the same length as that of the juvenile
Hoatzin {Opisthocomus) and is well suited to climbing (Heilmann,
1926). In modem birds the first digit is reduced and is
never robust, whereas in Deinonychus and Velociraptor the
first digit is relatively massive.
6. The proximal end of the first metacarpal is simple and
round. This appears to be another avian character unknown in
dinosaurs.
7. The first and second phalanges of the second digit form a
high, sharp ridge on their dorsal surfaces. This ridge assists in
the attachment of the primary feathers and is not known in
Deinonychus or Velociraptor.
8. The distal end of the first phalanx of the second digit anteroposteriorly
is as wide as, or slightly wider than, the proximal
end. In theropod dinosaurs such as Deinonychus, Oviraptor,
and Omitholestes, the first phalanx of the second digit is
wider proximally than distally. In Archaeopteryx the posterior
margin of the distal portion of this phalanx is slightly convex in
shape compared with the concave posterior margin in dinosaurs.
Both of these characters become progressively more advanced
in Confuciusomis, Cathayomis (Zhou et al., 1992), and
modem birds (Figure 4). In modem birds, the distal portion of
the first phalanx, together with the proximal portion of the second
phalanx, forms a prominently expanded convex posterior
margin of the main digit, which provides a combined, solid,
bow-shaped support for the primary feathers.
We should note that the above-mentioned characters are not
functionally independent from each other. They are mostly a
result of the morphological requirements of feathered flight.
Confuciusomis is the only other bird known with an Archaeopteryx-like
morphology in the manus. It also is probably the
oldest bird known except Archaeopteryx. All of the above characters
that can be ascertained are present in Confuciusomis, the
most notable being characters 1, 4, 6, and 8. Character 3 also
appears to be recognizable in the holotype of Confuciusomis,
although the wrist area is somewhat cmshed.
Conclusions
Ostrom (1976) argued that the chief difference between the
hands of Archaeopteryx and those of theropods is one of size,
all of the theropods being larger. Also, the fingers are relatively