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336 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY
ince (Hou, Zhou, Martin et al., 1995; see also Hou, Zhou, Gu et
al, 1995; Hou et al., 1996). Although these authors pointed out
that the chronology of the Yixian Formation was far from being
settled, their paper was entitled "A Beaked Bird from the
Jurassic of China," and thus Archaeopteryx's "new partner"
was heralded as such by the press. Doubtless, in combining a
modem-looking, toothless snout with short wings bearing massive,
large claws, Confuciusomis is of extreme relevance. Yet
whether it compares in age with Archaeopteryx or not is an issue
that still needs to be analyzed, especially now that new radiometric
dates have placed the Yixian Formation in the Early
Cretaceous, with dates of roughly 121 million years (Smith et
al., 1995, 1996).
3. THE PHYLOGENETIC POSITION OF THE ENANTIORNITHES
AND THE MONOPHYLY OF "SAURIURAE."—Many of the new
early fossils show a number of derived features that were first
reported in an array of mostly disarticulated elements from the
Late Cretaceous of Argentina, which C. Walker named Enantiornithes
(Walker, 1981). The new cohort of fossils has
shown not only that the Enantiornithes are tme birds (confirming
the perceptiveness of Walker's early observations), but
that they formed a large and diverse clade of Mesozoic fliers
as well.
In his original paper, Walker (1981) regarded the Enantiornithes
as phylogenetically intermediate between Archaeopteryx
and modem birds. In 1983, L. Martin proposed a basal
avian dichotomy leading to modem birds on the one hand, and
to Archaeopteryx and the Enantiornithes on the other (Martin,
1983). Martin's characters in support of the close relationship
of Archaeopteryx and the Enantiornithes, a group for which he
rescued Haeckel's term "Sauriurae," ranged from being regarded
as "not one" (Steadman, 1983:342), to "cannot be
shown to exist" (Olson, 1985:94), to "either plesiomorphic or
uncertain" (Chiappe, 1995b:60). At the same time, the nonmonophyletic
status of the Sauriurae has been broadly disregarded
in numerous cladistic analyses (e.g., Cracraft, 1986;
Chiappe, 1991, 1995b, 1996; Sanz and Buscalioni, 1992; Chiappe
and Calvo, 1994; Sanz et al., 1995, 1996; Forster et al.,
1996a). Yet in recent years, Martin's hypothesis has been renewed
with the addition of more characters and defenders
(e.g., Hou, Zhou, Martin et al., 1995; Kurochkin, 1995; Martin,
1995b; Zhou, 1995b; Feduccia, 1996; Hou et al., 1996).
What does not seem to emerge from the discussions of these
authors is the realization of the fact that an enormous amount
of convergence (and its corollaries) has to be explained for the
hypothesis of the monophyly of the Sauriurae to be seriously
entertained (see below).
The Roundtable Discussion
THE PHYLOGENETIC POSITION OF Mononykus.—The debate
was opened by L. Martin asking A. Elzanowski "whether
Mononykus can be embedded somewhere in the same scheme
where we have Oviraptor and ornithomimids." At one of the
regular presentations of the Symposium on Mesozoic Birds
that morning, Elzanowski had presented a cladogram, based
on cranial data, supporting the idea that Oviraptor was closer
to modern birds than is Archaeopteryx. In other words, Oviraptor
was regarded as a flightless bird. In responding to Martin,
Elzanowski posited that Mononykus "would be on an earlier
branch than Archaeopteryx," but added, "I would easily
agree that Mononykus is closer to birds than a typical
theropod... [yet] I cannot provide evidence in support of
Mononykus [having] been related to birds." Martin then asked,
"Do you think it [Mononykus} is related to Oviraptor?" Elzanowski
disregarded that alternative, saying he could not think
of any potential synapomorphy between Mononykus and Oviraptor.
Martin asked, "Do you think [Mononykus] is a more
advanced bird than Oviraptor?" Elzanowski replied, "I don't
think so."
This initial exchange between Martin and Elzanowski was
followed by J. Ostrom who, with intense democratic spirit, inquired,
"How many people here believe Mononykus is a bird,
and why?" The almost palpable hesitation of the audience was
broken by L. Witmer who, after acknowledging that he had reviewed
some of the papers defending the hypothesis of avian
relationships (and had seen the material as well), asserted that
"they [A. Perle, L. Chiappe, M. Norell, and J. Clark] have argued
appropriately with the data they have. ... I think they
have scored the specimens honestly and put them into their
analysis, and they [the specimens] fell out between Archaeopteryx
and modem birds." Put another way, Witmer was taking
up the issue that part of the disagreement, as L. Chiappe put it,
"is more related to methodological issues."
The atmosphere of hesitation evolved into one of critical,
scientific evaluation of the available data when P. Sereno surmised
that there could be "crucial data from the skull of the
excellent specimens, and perhaps that would be the decisive
data." Chiappe then projected the slides of two new, nearly
complete skulls of Mononykus from Ukhaa Tolgod (collected
in 1994 and 1995, and still unpublished), pointing out that "the
jugal bar is rod-like... there is not even a slightly ascending
process for its contact to the postorbital [bone]... [yet] there is
a postorbital like in Archaeopteryx." The audience followed
up with numerous questions about specific anatomical features.
P. Biihler inquired about the relationships of the two
heads of the quadrate to other bones, which articulated with
both the braincase and the squamosal, and was puzzled by the
fact that the external nares open at the tip of the snout, saying,
"It looks like a kiwi." S. Chatterjee asked about the shape of
the orbital process of the quadrate, which is broad as in other
basal birds (e.g., Archaeopteryx, Enantiornithes, Patagopteryx)
and, as Chiappe remarked, "not a pointy, typical ornithurine
quadrate." Elzanowski and S. Olson followed with
questions about the condition of the dentition, to which Chiappe
responded, "there are teeth in the mandible and those are
set in a groove...their crowns are not serrated...they look
quite like those of birds.... [There] may be a few teeth [in the