Postembryonic Ontogeny of the Spadefoot Toad, Scaphiopus intermontanus (Anura: Pelobatidae): External Morphology

Abstract

We provide a detailed description of and a staging table that portrays the ontogeny of the Great Basin spadefoot (Scaphiopus intermontanus Cope) from the just-hatched larva through the adult. We concentrate on the development of external morphological characters as observed in individuals raised under controlled laboratory conditions. We suggest that our staging table, besides providing greater detail, is more appropriate than a generalized staging table for describing the ontogeny of species within Scaphiopus. Also, unlike other staging tables, we delineate stage bound- aries. We recommend the use of stage boundary criteria for the construction of all future staging tables. Our findings indicate that some aspects of Scaphiopus ontogeny may be unique. Unlike other anuran larvae with sinistral spiracles, the operculum in S. intermontanus does not pass through a stage in which there are two separate openings. Other features, such as mouthpart characteristics, may be useful for intrageneric larval identification; however, we show that at least the labial tooth-row formula variation is affected by both rearing temperature and geographic origin of the specimen sample. Finally, rearing conditions possibly affect the timing of certain developmental events in S. intermontanus. Specifically, the timing of hindlimb differentiation seems to be labile relative to when differentiation occurs in other morphological features. table DETAILED DESCRIPTIONS of the ontog- eny of embryonic, larval, metamorphic, and postmetamorphic frogs (Anura) are important for understanding the general pattern(s) of development of representa- tive taxa and, by comparisons of different patterns, for resolving questions about sys- tematic relationships. For anurans, staging tables are a condensed way of describing ontogenetic changes. In a review of the lit- erature, Fox (1984:30) indicated that of the few thousand known species of anu- rans there are complete staging tables- fertilized egg through the completion of metamorphosis-for fewer than 20 spe- cies. Just et al. (1981: their Table 3) com- pared the staging tables of a number of these species. Most of the tables that have been constructed are for species contained in the genera Bufo and Rana. Two of the most detailed tables, for the African