Osteology and Evolution in Neotropical Bufo

Abstract

Members of five species groups of Neotropical Rufo were examined osteologically. Representatives of the guttatus group possess broad frontoparietals which fuse with the pro-otics late in ontogeny; the neural spines of these species are greatly roughened. Affinity with the African B. mauritanicus, B. superciliaris and regularis species group and with the Asian B. asper is suggested. The marinus group displays broad frontoparietals in fusion with the pro-otics and cristation patterns similar to the Central American and Mexican valliceps group. Toads of the granulosus group possess closed orbits, intense dermal coossification, and frontoparietals of broad and intermediate width; these conditions are possibly secondarily derived. The spinulosus group comprises both broad and narrow frontoparietal typos which may represent separate major evolutionary lines. The monotypic variegatus group appears closely related to the narrow frontoparietal members of the spinulosus group. INTRODUCTION Recently, much evolutionary research has been directed toward the genus Bufo. Baldauf (1955, 1958, 1959) has employed histological reconstruction in comparisons of cranial morphology. Evidence from paleontology and osteology has been utilized by Tihen (1960, 1962a,b; in press) toward systematic ends. Morphological and several biochemical approaches have been applied by Cei and various colleagues (1960, 1962, 1966) to South American species. Guttman (1967) has investigated blood proteins in Bufo using starch-gel electrophoresis, while Bogart (1968) has employed cytogenetic analysis in his research. The mechanics of vocalization of many bufonids have been compared by W. F. Martin (1967). During this time, Blair (1962, 1963, 1964, 1966; in press), utilizing artificial hybridization and other techniques, has developed a comprehensive evolutionary scheme for Bufo. Nevertheless, many opportunities for question and confirmation exist and provide stimuli for further investigation. MATERIALS AND METHODS This report presents and analyzes osteological data for five Neotropical species groups of Bufo; relevant species from other continents are also discussed in detail. Sample size is indicated in parentheses after the specific name. Debatable species status is indicated by question marks directly succeeding taxa. Species group assignation generally follows that of Blair (in press). Skeletonization was by treatment with dilute sodium hypochlorite (Sanders, 1953) or by dermestid beetle larvae. Osteological details of 1 Based in part on a doctoral dissertation submitted to The University of Texas at Austin. 2 Partial support was provided by a National Science Foundation Summer Traineeship in Environmental and Systematic Biology.