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relatives among the flamingos (Phoenicopteridae) (Olson and
Feduccia, 1980; Peters, 1987). The observed similarities in
these two fossil taxa thus suggest a systematic proximity of
Anseriformes and Phoenicopteridae. This corroborates the conclusion
drawn in an extensive phylogenetic analysis (Ericson,
1997) of nonpasserine families (Figure 1).
SKULL.—The only cranial element found of Juncitarsus
gracillimus is an unfused frontal bone that suggests that Juncitarsus
has a deeper depression for the supraorbital salt
gland and a more rounded margo interorbitalis than does
Presbyornis.
VERTEBRAE.—No direct comparison between supposedly
homologous cervical vertebrae in Juncitarsus and the Presbyornithidae
has been possible. In general, the upper cervicals of
Juncitarsus seem to be elongated, resembling those of the
Phoenicopteridae (Peters, 1987). No such elongated vertebrae
have been observed in Presbyornis. Olson and Feduccia (1980)
described a cervical vertebra of Juncitarsus comparable to the
16th of Phoenicopterus and the 15th of Phoeniconaias. They
stressed the similarities between the Phoenicopteridae and Juncitarsus
and specifically pointed out the flat, elongated ventral
surface with two distinct anterior hemapophyses, along with
the presence of a large, sloping neural crest. In Presbyornis the
ventral surface is flat, too, with distinct anterior hemapophyses.
The corpus is considerably narrower in ventral aspect in Presbyornis,
however, and no vertebra with a high neural arch has
been observed. The posterior cervical vertebrae in Presbyornis
closely match the corresponding ones in the Anseranatidae and
certain charadriiform birds, such as the Scolopacidae.
The thoracic vertebrae in Juncitarsus are most probably not
pneumatized, unlike the Presbyornithidae. Otherwise their
morphologies are very similar in being laterally compressed
and possessing a well-developed neural spine. This morphology
is rather different from that of the Phoenicopteridae but
agrees with that of the Charadriiformes. Given the phylogenetic
relationships of these taxa (Ericson, 1997), this might be
symplesiomorphic.
STERNUM.—It was possible to compare only the manubrial
region of the sternum, which showed no differences.
CORACOID.—Juncitarsus differs from the Presbyornithidae
in having processus acrocoracoideus relatively larger and triangular
and facies articularis clavicularis excavated (Figure 2).
FURCULA.—Only the symphyseal part is known of Juncitarsus,
which seems to be more flattened and narrower than in the
Presbyornithidae.
SCAPULA.—The craniodorsal margin of the scapula is
straight in Juncitarsus, whereas it is generally curved in the
Presbyornithidae, with the acromion pointing more dorsally
(Figure 3).
HUMERUS.—When comparing Juncitarsus gracillimus with
Presbyornis pervetus, which is of similar size, the humerus
seems much more slender in Juncitarsus. In the proximal end,
Juncitarsus differs considerably from the Presbyornithidae in
having the caput humeri not undercut at all (deeply undercut in
FIGURE I.—Phylogenetic position of the Presbyornithidae (from Ericson, 1997). Note the anseriform affinity of
the Presbyornithidae and the proximity of the unresolved polychotomy that includes the flamingos, Phoenicopteridae,
to the anseriforms.