The Neotropical Colubrid Snake Fauna (Serpentes: Colubridae): Lineage Components and Biogeography

Abstract

Previously developed phylogenetic hypotheses for Neotropical colubrids are used as a framework to interpret the biogeographic history of these lineages. The distributions of members of two lineages of xenodontines, which comprise most of the Neotropical colubrid fauna, are documented. One lineage, the Central American clade, has its greatest generic di- versity throughout Central America and is poorly represented in North and South America. In contrast, the other major Neotropical xenodontine lineage shows its highest generic diversity in Amazonian and southern South America. Species richness patterns for each clade generally correspond with those shown at the generic level, with the exception that the Central American component has a high species richness in the Andes of Colombia and Ecuador due primarily to the presence of a large number of species of Atractus. Significant dispersal by Central American xenodontines into South America is inferred, but South American xenodontines are poorly represented outside South America. The major phyletic separation of Neotropical xenodontines into Central and South American clades is inferred to result from a late Cretaceous or early Tertiary vicariance or concordant dispersal event. This pattern corresponds to that shown by other components of the Neotropical biota. The relationships of the West Indian xenodontines do not conform to the commonest pattern predicted by general biogeographic models for the Caribbean; moreover, the suggested temporal framework for this radiation implicates dispersal as a plausible mechanism for its deployment. Xenodontines are suggested to be the oldest members of the Neotropical colubrid fauna, and probably date from the late Cretaceous or early Tertiary in that region. Their earlier history is uncertain, and may be with either northern taxa or with a Gondwanan-derived fauna in South America. Colubrines and natricines are much more recent components of the Neotropical fauna. For investigating mechanisms in historical biogeography, the desirability of deriving temporal estimates for the separation of major com- ponents of a biota independently of biogeographic considerations is emphasized. (Snakes; Col- ubridae; xenodontine; Neotropics; Central America; South America; biogeography; vicariance; West Indies.)