. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Fig. 21. Variation in the size and shape of the casque of Crox mitu. Upper left: young bird (age d'A months). Upper right; adult female. Lower, left and right: adult male. (Photographs courtesy John A. Griswold and Zoological Society of Philadelphia.) Huila, Colombia, and in the Marcapata Val- ley, Cuzco, Peru. In either case it is diffi- cult to account for the disjunctions, but one may sumiise that among such sedentary and territorial birds as Crox paiixi and Ti- namiis osgoodi extinction can occur in con- tinental
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Fig. 21. Variation in the size and shape of the casque of Crox mitu. Upper left: young bird (age d'A months). Upper right; adult female. Lower, left and right: adult male. (Photographs courtesy John A. Griswold and Zoological Society of Philadelphia.) Huila, Colombia, and in the Marcapata Val- ley, Cuzco, Peru. In either case it is diffi- cult to account for the disjunctions, but one may sumiise that among such sedentary and territorial birds as Crox paiixi and Ti- namiis osgoodi extinction can occur in con- tinental forest areas as readily as in island areas. DISCUSSION From the analysis of variation and distri- bution, it can be seen that Penelope and Crax show the same basic patterns of speci- ation. In both these genera, the members of a species-group are mostly allopatric representatives of one or more superspecies. These representatives, or species, are, for the main part, in a relatively early stage of speciation. Whether they should be called species or subspecies is not always easy since the criterion of interbreeding in na- ture can not be applied as it could with sympatric species. In the case of Crax in particular, moq^hological divergence might lead to the belief that the various forms have reached levels of speciation beyond those actually attained. The evidence of hybridization in captivity, but not in the wild, is here a far better criterion than mor- phology alone since it indicates that an intennediate stage in the development of the isolating mechanism has been reached (, there is little genetic isolation).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Harvard University. Museum of Comparative Zoology. Cambridge, Mass. : The Museum
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