A new species of Thamnodynastes from the open areas of central and northeastern Brazil (Serpentes: Dipsadidae: Tachymenini)

The genus Thamnodynastes Wagler, 1830 is currently composed by nineteen species of viviparous and opisto-glyphous snakes, largely distributed in South America, from Colombia to Argentina. The analyses of a large data set of specimens from South American collections evidenced one unknown species from the open formations of central and northeastern Brazil, which is described here. The new species is distinguished from all its congeners by a unique combination of characters, including 19 dorsal rows of smooth scales on the midbody, the smallest number of subcaudals in the genus, and a distinct hemipenial morphology and coloration pattern. To define this new species we present robust diagnostic characters and discuss comparisons with other species of this diverse and taxonomically complex genus of Neotropical snakes.