Revision of the neotropical snake genus Chironius Fitzinger (Serpentes, Colubridae)

Abstract

The snake genus Chironius Fitzinger is revised. This genus occurs from sea level to 2800 m from northern Honduras southward through Central America across northern South America and east of the Andes to Uruguay and northern Argentina. Snakes of this genus are relatively common and possess 10 or 12 scale rows at midbody, a unique feature among Neotropical serpents. Traditionally, the species of Chironius have been taxonomically abused and confused because of superficial similarities among the species and because of the occurrence of great intraspecific variation, ontogenetic changes, and sexually dimorphic []. I recognize 13 species and a total of 20 taxa in Chironius and describe four new taxa, C. dixoni, C. fuscus leucometapus, C. multiventris septentrionalis, and C. quadricarinatus maculoventris. Chironius exoletus (Linnaeus) has long been unrecognized, but I considered it a valid species. Other recognized taxa are C. bicarinatus (Wied), C. carinatus carinatus (Linnaeus), C. carinatus flavopictus (Werner), C. carinatus spixi (Hallowell), C. flavolineatus (Jan), C. fuscus fuscus (Linnaeus), C. grandisquamis (Peters), C. laevicollis (Wied), C. monticola Roze, C. multiventris cochranae Hoge and Romano, C. multiventris foveatus Bailey, C. multiventris multiventris Schmidt and Walker, C. quadricarinatus quadricarinatus (Boie), C. scurrulus (Wagler), and C. vincenti (Boulenger). Character summaries for the genus and a key for identifying all species are offered. The species accounts provide a synonymy, diagnosis, complete description, distribution map, discussion of variation, and life history information for each taxon. The Cenozoic history of Central and South America is summarized, and an evolutionary-zoogeographic scheme is proposed for the species of Chironius based on the phylogenetic principles of Hennig. The Amazonian rainforest is hypothesized as the center of speciation and radiation for Chironius. Based on squamative, dentitional, and hemipenial features, Dendrophidion is viewed as the genus most closely related to Chironius. The final section summarizes the major taxonomic changes in nomenclature.