Integrated evidence sheds light on the taxonomy of the widespread Tantilla melanocephala species complex (Serpentes: Colubridae) and indicates the existence of a new species from southern South America

The widespread Tantilla melanocephala is a South American snake, which has a convoluted taxonomic history and a poorly addressed systematics. The taxonomic identity and the phylogenetic affinities of their populations are unclear, suggesting the existence of a complex of undescribed species. Here, we preliminarily address the morphological diversity and genetic structure of the T. melanocephala complex through comparative morphological approaches and phylogenetic analyses using maximum likelihood. Our results confirm the presence of hidden diversity within the T. melanocephala complex and strongly indicate that the populations of T. melanocephala from southern South America represent a distinct lineage, which is morphologically diagnosable under a unique combination of character states. Therefore, we formally describe these populations as a new species and present a comparison among all other South American species of Tantilla. We also estimate the divergence times of the main clades within the complex through Bayesian analysis, suggesting a biogeographical scenario of lineage diversification. Finally, our study clarifies aspects of the intricate taxonomy of the T. melanocephala complex, providing a framework for future studies to avoid the description of synonyms.