Ptyas mucosa

Ptyas mucosa (Linnaeus, 1758) Fig. 4 A Material. One trunk vertebra (ASIZF 0101050). Description. In anterior view, the cotyle appears rounded and flanked by paracotylar foramina. The neural canal is large and circular. The prezygapophyses are well-developed, with the ending portions of their accessory processes prominently directed forward and slightly ventrally inclined. The zygosphene roof is straight, and its articular facets are dorsally tilted. In posterior view, the condyle is rounded and the neural arch is depressed (vaulting ratio = 0.24), with paired endozygantral foramina visible. In ventral view, the centrum is elongated and triangular in shape. Subcentral foramina are present, and both subcentral grooves and ridges are clearly defined. The haemal keel is well-developed and oblanceolate. Postzygapophyseal articular facets are oval. Epizygapophyseal spines are developed and directed posterolaterally. Diapophyses and parapophyses are clearly visible, though the parapophyseal processes are absent. In dorsal view, the vertebra is slightly laterally compressed. The anterior margin of the zygosphene is straight with two small, blunt lateral lobes. The posterior median notch is markedly deep. Prezygapophyseal articular facets are oval, and the prezygapophyseal accessory processes are well-developed, pointed, and directed anterolaterally. In lateral view, the interzygapophyseal and subcentral ridges are straight. The neural spine is damaged. The lateral foramina are observed. Remarks. The fossil vertebra can confidently be attributed to colubrids or “ colubrines ”, further supported by several combined features: a well-developed haemalkeel (instead of a hypapophysis), the presence of paracotylar foramina, a pronounced division between the para- and diapophyses, and a moderately high neural spine. Moreover, its overall vertebral morphology closely matches that of Ptyas, which share characteristics such as epizygapophyseal spines, pointed prezygapophyseal accessory processes, and distinct subcentral grooves and ridges (see Ikeda 2007; Shi et al. 2023). The strongly anteriorly directed prezygapophyseal accessory processes, however, are a distinctive feature seen only in the two extant Ptyas species from Taiwan, Ptyas major (Günther, 1858) and Ptyas mucosa (Linnaeus, 1758) (see Chen 2020). Among these, P. major is a medium-sized species, while P. mucosa notably larger, and the vertebrae of P. major are consistently smaller than those of Ptyas mucosa, as seen in our comparative specimens (Fig. 4 B, C).