Revision of the Chironius bicarinatus complex (Serpentes: Colubridae): Redefined species boundaries and description of a new species

Currently, the proposed diagnoses for the Chironius bicarinatus complex reflect a wide variation in color pattern and pholidosis. Herein, we review the Chironius bicarinatus complex based on morphological and molecular data from a sample of 485 specimens covering the species distribution. Our results corroborate the recognition of C. bicarinatus and C. gouveai, and diagnose a distinct lineage without an available name. Thus, here we describe this new species restricted to the Baturite Massif, a relictual rainforest isolated in the Caatinga xerophytic domain, in the state of Ceara, northeastern Brazil. The new species can be distinguished from its congeners by its unique combination of qualitative and quantitative morphological characters (scale counts, morphometric, color pattern), and is also supported by molecular and ecological evidence. Additionally, we rectify data on the distribution and morphological variability of C. gouveai to accurately infer the boundaries between this taxon and C. bicarinatus, which was not properly addressed. Finally, we discuss our results in the light of previous studies that suggest diversification hypotheses in the Atlantic Forest already detected for other taxa, highlighting the importance of conserving the areas of "Brejos de Altitude", in northeastern Brazil, and the southern limit of Serra do Mar up to Serra do Tabuleiro, in southern Brazil.