Kukri snakes Oligodon Fitzinger, 1826 of the Western Palearctic with the resurrection of Contia transcaspica Nikolsky, 1902 (Reptilia, Squamata, Colubridae)

The kukri snakes of the genus Fitzinger, 1826 reach the westernmost limits of their distribution in Middle and Southwest Asia (Afghanistan, Iran, and Turkmenistan), and the Palearctic portions of Pakistan. In this article, we review the systematics and distribution of the two species native to this region, (Shaw, 1802) and (Jerdon, 1853) based on an integrative approach combining morphological, molecular, and species distribution modeling (SDM) data. Phylogenetic analyses recover populations from Iran and Turkmenistan in a clade with the species complex, rendering the former species paraphyletic relative to stricto on the Indian subcontinent. To correct this, we resurrect the name Nikolsky, 1902 from the synonymy of and assign it to populations in Middle-Southwest Asia. So far, is known only from the Köpet-Dag Mountain Range of northeast Iran and southern Turkmenistan, but SDM mapping suggests it may have a wider range. Genetic samples of from northern Pakistan are nested in a clade sister to the recently described Mirza, Bhardwaj & Patel, 2021, and are phylogenetically separate from stricto in south India and Sri Lanka. Based on morphological similarity, the Afghanistan and Pakistan populations are assigned to (Daudin, 1803) and we synonymize with this species. Our investigation leads us to remove from the snake fauna of Afghanistan, Iran, and Turkmenistan, with the consequence that only and are present in these countries. Additional studies are needed to resolve the taxonomy of the and species complexes on the Indian subcontinent, and an updated key for both groups is provided.