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NUMBER 89 229
FIGURE 9.—Right tibiotarsus of (A) Chauna chavaria (USNM 347738) in anterior view, compared with paratypical
tibiotarsi of Chaunoides antiquus, n. gen. n. sp.: B, MNRJ 4628-V; C, MNRJ 4626-V; D, MNRJ 4627-V; E,
MNRJ 4625-V; F, MNRJ 4631-V; G, MNRJ 4629-V. (Scale bar=l cm.)
the bones are extremely pneumatized, especially the distal end
of the radius, the tendinal groove of the tibiotarsus, and the
proximal end of tarsometatarsus. This condition is not observed
in Chaunoides.
The distal end of the femur of Chaunoides is very similar
morphologically to that of the other anhimids, but the long
neck and the thin shaft give this bone an appearance more like
that of anatids, including Anseranas. In the tarsometatarsus of
Chaunoides, the higher intercotylar prominence is quite different
from that in extant screamers, but the hypotarsus, with only
two calcaneal ridges, is typical of the Anhimidae and also is
found in Paranyroca magna Miller and Compton, 1939, from
the lower Miocene of South Dakota, in contrast to that of the
remainder of the Anatidae, which have four calcaneal ridges.
The proportions of the femur, tibiotarsus, and tarsometatarsus
of Chaunoides suggest that it was slightly smaller than Chauna
chavaria, the smallest living screamer, and also more gracile,
with the leg bones more slender and with the skeleton less
pneumatized than in the living anhimids.
Conclusion
Chaunoides antiquus is the first fossil species of the family
Anhimidae to be recognized. At the Natural History Museum,
London (formerly the British Museum (Natural History)), in
1992, I examined the holotype of Loxornis clivus Ameghino,
1895 (placed in incertae sedis by Tonni (1980)), which is from
the Oligocene (Deseadean) of Argentina. I concluded that this
bird may be a representative of the Anhimidae, but because of
its poor preservation (only the distal end of a left tibiotarsus,
with the medial condyle incomplete), additional material would
be required to substantiate this hypothesis.