PDF (Lo-Res) - Smithsonian Institution Libraries

228
SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY
FIGURE 8.—The left femur of Chaunoides antiquus, n. gen. n. sp. (paratype MNRJ 4621 -V), coated with ammonium
chloride (right) compared with Chauna chavaria (USNM 347738) (left): A, anterior view; B, posterior
view; c, distal view. (Scale bar= 1 cm.)
shaft. In the proximal end of the tarsometatarsus (Figure 10),
the intercotylar prominence is higher and sharper than in other
Anhimidae; the morphology of the hypotarsus is very similar to
that in Chauna, especially in C. chavaria, but the crista medialis
is shorter and higher. Also, there is no pneumatic foramen in
the proximal end of the tarsometatarsus, whereas in extant anhimids
this region is very pneumatized.
Discussion
The procoracoid foramen in Chaunoides is large and perfectly
formed, as it is in the available specimens of Anhima and
some specimens of Chauna; however, in certain specimens,
such as Chauna chavaria (USNM 347738) and C. torquata
(HA 389), this foramen is not formed (Figure 5), a condition
possibly due to immaturity or to intraspecific variation. Olson
(1987) commented on this same variation in several genera of
Accipitridae as possible intraspecific or intrageneric variation.
The pneumatic foramen in the sterno-coracoidal fossa of
Chaunoides and Chauna is a very large opening with rounded
borders, being the extreme form of a condition that also is
found in Anhima, Anseranas, Opisthocomus, gruids, some galliforms,
and cathartids. In the three species of living anhimids,