The Spadefoot Toads in Oklahoma with a Summary of Our Knowledge of the Group

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Abstract
The American spade-foot toads, Scaphiopus, are divided morphologically into 2 subgenera, Spea and Scaphiopus. Classification of habitat, however, gives a xeric group consisting of subg. Spea and S. couchii of subg. Scaphiopus, and a mesic group of the other spp. of subg. Scaphiopus. Therefore, phylogenetic separation occurred before migration of the most of the subg. Scaphiopus from the s.-w. center of origin to more mesic habitats in the east. As bases for these interpretations, and as a summary of the literature, the author includes a key for adults and for tadpoles, a study of distribution with particular reference to Oklahoma, and observations on the protective, feeding, and reproductive habits of the spadefoots. Current myths arising from fossorial habits are exploded, and several expts. designed to determine resistance of the toad to drying are described. Interspecific breeding is evidently prevented by physiological (or psychological) factors, auditory response and clasping behavior, and by ecological preferences. Actaptation to xeric habitat may be observed in the carnivorous and cannibalistic activities of the tadpoles, their rapid growth rate, and in the breeding response of the adults to heavy or violent rainfall. Since xeric habits may be retained under mesic conditions with little or no negative selective value, the eastern spadefoots are anomalous in exhibiting xeric behavior under mesic conditions. Although the eastern types differ widely in many respects from the western, they must still be regarded as subxeric rather than as truly mesic.

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