ABSTRACT
This chapter arrives at an interesting and exciting time in the study of snake systematics. The last part of the 20th century and the early part of the 21st century might ultimately be highlighted as the intersection between traditional classifications of snakes based on morphology and those based on molecular data. Classification of organisms has typically and traditionally relied on morphological traits to guide the process, either by phylogenetic methods that attempt to be concordant with evolutionary history or by more arbitrary methods that apply the use of authoritative interpretation of morphology by experts in the field. Given the real possibility of evolutionary convergence among morphological characters in organisms, such as in snakes and other limbless squamates (see Wiens et al. 2006), it seems that having a credible understanding of relationships among extant serpents will be through the use of molecular systematics. Another advantage is that molecular systematics can provide thousands to millions of characters as well produce species tree relationships using independently evolving gene estimates free from linkage or convergence. However, there have been important studies using rigorous phylogenetic methods on a large suite of morphological characters scored from extant and extinct snakes (something molecular methods cannot address) that reveal the utility of these characters to address phylogeny (Lee and Scanlon 2002; Lee et al. 2007). Therefore, we are not saying that traditional classifications based on morphology are entirely incorrect; in fact many of them still hold up well. However, several studies are revealing that certain traditional groups
simply cannot be credible given the agreement among independently evolving genes (e.g., the traditional macrostomata, Anilioidea, Colubridae are all likely paraphyletic). Moreover, molecular methods will be more useful at examining relationships at the levels of species, genera, and families. Arriving at a strong consensus with robust trees among studies using unlinked genetic markers has already helped illuminate evolutionary relationships among snake species. These molecular studies inform taxonomy by naming groups that are concordant (i.e., monophyletic) with the evolutionary history of the taxon. These phylogenies ultimately help comparative biologists attain a better understanding of the independent origins of various morphological characteristics, ecologies and behavior.
