1 INTRODUCTION
Species diversity is central to biodiversity. Exploration of species diversity and identification of species distribution boundaries are pivotal to the preservation and management of biodiversity. The accumulation of multi-locus data and development of related analytical technologies have greatly advanced our understanding of cryptic species diversity. In recent decades, considerable progress has been made in the phylogeny of Asian snakes. Notably, various systematic issues have been addressed (Guo, Zhu, Liu, Wang, & Nguyen, 2020; Hou et al., 2021; Liu et al., 2021; Poyarkov et al., 2022) and an increasing number of new taxa have been described (Hou et al., 2021; Liu, Zhong, Wang, Liu, & Guo, 2018; Ren, Jiang, Huang, David, & Li, 2022). However, in comparison to well-studied common snake groups, such as Hebiusand Lycodon (Guo et al., 2013; Guo et al., 2014; Hou et al., 2021; Ren et al., 2022), little attention has been paid to rare snake species, such as those in the genus Sibynophis .
The family Sibynophiidae is comprised of only two genera, including the non-venomous genus Sibynophis . These snakes are characterized by their small body size, loose attachment of their dentary to the articular bone, and the presence of numerous small maxillary teeth of uniform size (Pope, 1935). Currently, nine species are recognized withinSibynophis , with primary distribution in South and Southeast Asia (Uetz, Freed, Aguilar, & Hošek, 2022; Wallach, Williams, & Boundy, 2014). Two species, S. collaris and S. chinensis , are known to occur in China (Wang et al., 2020; Zhao, 2006).Sibynophis chinensis was initially described based on a sole specimen from Yichang, Hubei, China (Günther, 1889), but is now known to occur in China, Korea, and Vietnam (Wallach et al., 2014). In China, the species exhibits broad distribution, ranging from southern Xizang in the west to Jiangsu in the east (Zhao, 2006). Three subspecies are currently recognized (Zhao, 2006; Zhao, Huang, & Zong, 1998), including S. c. chinensis , S. c. grahami , and S. c. miyiensis . In addition to the nominal species, which broadly occurs in Southwest, Central, and East China, S. c. miyiensis is endemic to Southwest Sichuan and Northwest Yunnan, while S. c. grahami is endemic to northeastern Yunnan and Guizhou (Zhao et al., 1998; Zhao & Yang, 1997). This taxonomical arrangement is followed by most authors (Uetz et al., 2022; Wallach et al., 2014; Wang et al., 2020). The type locality of S. collaris is in Assam, India (Gray, 1853), but the species is restricted to Xizang and Yunnan in China (Zhao, 2006; Zhao et al., 1998). Morphologically, the two species differ from one another by number of supralabials and anterior temporal scales only (Zhao, 2006; Zhao et al., 1998).
Due to their rare occurrence and elusive nature, few Sibynophisspecimens have been collected since their initial description and few studies have been conducted on their biology, particularly their systematics (Li et al., 2020; Pyron, Burbrink, & Wiens, 2013; Zaher et al., 2019). Although Sibynophis species have been included in certain phylogenetic studies (Chen et al., 2013; Li et al., 2020; Pyron et al., 2013; Zaher et al., 2019), only a limited number of samples have been examined. For example, Zaher et al. (2019) conducted a large-scale molecular phylogenetic study of advanced caenophidian snakes, which included five Sibynophis species, each with only one individual. Thus, given the small number of species and specimens studied, the diversity and evolution of the genus remain poorly understood.
Here, based on more extensive sampling, we explored species diversity of the genus Sibynophis and revised the taxonomy and distribution boundaries of each taxon within China.