Recent Progress in Taxonomic Studies, Biogeographic Analysis, and Revised Checklist of Reptiles in Indochina

The Indochinese Peninsula represents one of the key global biodiversity hotspots in Southeast Asia. The herpetofauna of Indochina (herein including Vietnam, Laos, Cambodia, and Thailand) currently (as by 10 August 2023) comprises 882 native and six invasive species of reptiles and is one of the richest in the world. About 40% of the Indochinese reptile species were discovered or recorded within the first two decades of the 21st century. We review the literature and our field data to assess all recent discoveries and taxonomic changes; we compile an annotated checklist of reptilian fauna of Indochina, including updated faunal lists for Vietnam and Thailand. Reptile species checklists for Laos and Cambodia are published for the first time. For each species we provide the following information: scientific name; recommended common name in English; information on type specimens; information on recognized subspecies; type locality; data on its distribution within Indochina and beyond; IUCN conservation status; taxonomic comments and the most important references. We review the distribution of each reptilian species across the 23 biogeographic subregions of Indochina, estimate the similarity among the regional faunas and evaluate their species richness and endemism. In total, we record 882 native reptile species belonging to three orders, 34 families and 163 genera; of them 408 species (46.3%) are endemic to Indochina. Comprising 512 known species, the reptilian fauna of Thailand is the richest (114 country endemics, 22.3%), followed by Vietnam with 496 species (157 endemics, 31.7%), Laos with 250 species (39 endemics, 15.6%), and Cambodia with 191 species (15 endemics, 7.9%). A cluster analysis of faunal similarity between the subregions revealed three major groupings, corresponding to the Sundaland fauna south of the Isthmus of Kra, the subtropical fauna of northeastern Indochina, and the tropical fauna of mainland Indochina. Within the latter grouping four clusters can be distinguished: (1) northern, central and southern Annamites, (2) western Indochinese subregions, (3) central-south Vietnam lowlands including the Bolaven Plateau and Cardamom Mountains, (4) and the depleted faunas of river deltas, coastal areas and offshore islands. We identify the Northern, Central and Southern Annamites, the Northwest Uplands of Vietnam, Laos and Thailand, Southern Tenasserim in Thailand as the major centers of reptilian diversity in Indochina. The highest number of Indochinese endemic reptilian species was recorded in Central-Southern Vietnam Lowlands, Northern Annamites, and Central Annamites. The analysis of reptilian distribution patterns suggests the presence of 20 clusters of species sharing similar distribution patterns across Indochina. Our results further underline the key role of Indochina as an important area for diversity and conservation of reptiles. Among 882 native species of Indochinese reptiles, 356 species (40.4%) are considered as Data Deficient (DD) or were Not Evaluated (NE) according to the IUCN Red List criteria, while 106 species (12.0%) were considered Vulnerable (VU), Endangered (EN) or Critically Endangered (CR), 17 species (1.9%) were considered to be Near Threatened (NT), and 403 species (45.7%) to be of the Least Concern (LC) status. Our work has implications for elaboration of further conservation efforts for Indochinese reptiles on regional and global levels, as well as for a better understanding of the biogeographic patterns of reptilian richness and endemism in Asia.