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Ichthyornis paper



Just out:

Clarke, J. A. 2004. Morphology, phylogenetic taxonomy, and systematics of
Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American
Museum of Natural History 286: 1-179.

    "Charles Darwin commented that Ichthyornis, as one of the ³toothed
birds² from the Late Cretaceous of Kansas, offered some of ³the best support
to the theory of evolution² (in litt., C. Darwin to O.C. Marsh, August 31,
1880). Ichthyornis figures no less prominently today. It is one of the
closest outgroups to crown clade Aves, and remains one of the only Mesozoic
avialans known from more than a handful of specimens. As such, Ichthyornis
is an essential taxon for analyses of deep divergences within Aves because
of its influence in determining the morphologies ancestral to the crown
clade.
Ichthyornis, however, has languished in need of new anatomical description
and taxonomic revision. Many of the best Ichthyornis specimens were largely
inaccessible, plastered into Yale Peabody Museum (YPM) exhibit mounts for
nearly a century. The focus of this study was the entire YPM Ichthyornis
collection, the largest at any institution.
The elements removed from the mounts were identified to the specimens with
which they were originally associated. Detailed morphological study of the
81 YPM specimens yielded the following results: (1) there is evidence for
only one species of Ichthyornis, rather than the eight previously proposed;
(2) 78 specimens are part of this species, Ichthyornis dispar; (3) two
previously identified species are not part of Ichthyornis; and (4) one new
species is identified. This analysis also provided a case study in the
application of phylogenetic nomenclature at the species level. The
morphology of Ichthyornis dispar is described in detail from the holotype
and referred specimens.
Phylogenetic analyses of 202 morphological characters, scored for 24
terminal taxa, evaluated the relationships among Mesozoic ornithurines
including Ichthyornis dispar and the newly identified taxa. Analysis of 23
core taxa produced two most parsimonious trees (L: 384, CI: 0.66). Marsh's
³Ichthyornithiformes² is not monophyletic: Two previously named species of
Ichthyornis as well as Apatornis celer are placed as more closely related to
or as part of Aves. The results of the phylogenetic analyses have
implications for previous hypotheses of the timing and pattern of the origin
of Aves."

    Kudos to Julia Clarke for this very detailed and well-researched paper,
I must say :-). A couple of things that caught my attention:
    The frontispiece is a reconstruction of _Ichthyornis_ based on the
results of the paper. I'll leave it to others to comment on how accurate the
illustration is (I wouldn't be able to even guess), but it was nice to see
an _Ichthyornis_ reconstruction that obviously involved a bit more attention
to the actual specimens than the normal, older reconstructions we're
probably more used to, which were basically made by sticking teeth on a
tern.
    As it says in the abstract, Clarke reduces all the species of
_Ichthyornis_ (except those that actually are not ichthyornithids) to one,
which she calls _I. dispar_. Clarke explains that she is not directly using
the ICZN to name her taxa (she's following the draft PhyloCode), so I can't
quite comment on her synonymies. Note, however, that under the ICZN, the
correct name for this species would be _I. anceps_, not _I. dispar_ - while
_I. dispar_ is the type species of the genus, _anceps_ was named earlier,
and so takes priority even though it was originally in a different genus.
    Also hidden in the paper is the coining of the name 'Pangalliformes' for
the total group of Galliformes. The reason given for the coining is that 'It
is proposed here for increased precision, as one of the fossils addressed in
this document would be Pangalliformes incertae sedis but there is no
evidence that it is part of the galliform crown clade'. However, as far as I
can see from a brief skim of the paper (so I may be missing something),
there is nothing to directly say that it is *not* part of the crown. In such
a case, I personally would have preferred to call it 'Galliformes incertae
sedis' and so avoid making a whole new name to keep track of (I'm
potentially distinguishing between 'incertae sedis' [uncertain position in
the clade, and/or potentially not part of it] and 'sedis mutabilis'
[uncertain position within the clade, but definitely part of it]). What do
others think about this? Economy of taxon names, or maximum precision?

    Cheers,

        Christopher Taylor