Xenopeltis Reinwardt in Boie , 1827

Szyndlar, Zbigniew & Georgalis, Georgios L., 2023, An illustrated atlas of the vertebral morphology of extant non-caenophidian snakes, with special emphasis on the cloacal and caudal portions of the column, Vertebrate Zoology 73, pp. 717-886 : 717

Xenopeltis Reinwardt in Boie, 1827

Material examined.

Xenopeltis unicolor Reinwardt in Boie , 1827 (FMNH 178973; FMNH 191771; MGPT-MDHC 117; MNHN-AC-1909.0007; NCSM 84957 [Morphosource.org: Media 000070181, ark:/87602/m4/ M70181 ]; NHMUK 66.7.10.6; NHMUK 1930.5.8.133-135) .

Description (Figs 128-136).

Trunk vertebrae. Centrum distinctly longer than wide; cotyle and condyle orbicular; neural arch moderately vaulted; posterior median notch of the neural arch deep; neural spine low, not standing higher than the junction of the posterior margins of the neural arch and forming thus a continuous Y-shaped ridge, occupying the posterior half of the neural arch; prezygapophyseal accessory processes short; hypapophyses restricted to anterior vertebrae (they disappear after V 40-V 45), elongated and thin in the anteriormost ca. 10-15 vertebrae but in the succeeding ones, plate-like, with a distinct notch in its ventral edge, visible in lateral view (condition observed in all of our specimens examined [as well as in Gasc’s [1974: fig. 24] figured specimen; a feature unknown in other snakes); haemal keel well-developed, in mid-trunk vertebrae ridge-like, in posterior trunk vertebrae flattened, approaching or exceeding the width of the cotyle; subcentral grooves deep; well-developed subcotylar tubercles in posterior trunk vertebrae; paracotylar foramina absent.

Trunk / caudal transition. The haemal keel of the last trunk vertebra(e) is wider than in more anterior vertebrae. Its posterior end broadens gradually in succeeding vertebrae of the cloacal region and then bifurcates, giving rise to haemapophyses. In four of the examined specimens, the first haemapophyses appear on the first or second caudal vertebrae. In the remaining three, however, they appear yet on the last (or on the penultimate) cloacal vertebra, the condition almost not occurring in all other extant non-caenophidians (but see also Epicrates above and Morelia below, for other similar, but also intraspecifically variable, exceptions).

Smith (2013) highlighted the presence of longitudinal, bilateral ridges where there should be situated the zygantral mounds of other constrictors, with these ridges being particularly well developed on middle and caudal vertebrae, which he regarded, along with the prominent subcotylar tubercles and the shape of the neural spine, as autapomorphic features of Xenopeltis unicolor (they could potentially be autapomorphic of the genus as a whole, but X. unicolor was the only species available for study to both Smith 2013 and to us).

Number of vertebrae (all for Xenopeltis unicolor ). MGPT-MDHC 117: 222 (188+3+31); NCSM 84957: 220 (187+4+29); MNHN-AC-1909.0007: 218 (186+3+29); FMNH 191771: 211 (178+3+30); FMNH 178973: 207 (173+4+31). The counts of caudal vertebrae include final fusions, present in all specimens.

Data from literature and unpublished data from personal communications: Xenopeltis hainanensis Hu & Zhao in Zhao, 1972: 165 trunk and cloacal vertebrae plus 20 caudal vertebrae (IVPP OV 2752; Jingsong Shi, unpublished data, personal communication to GLG); Xenopeltis intermedius Orlov et al., 2022: 172 trunk and 25 cloacal and caudal vertebrae (estimated from Orlov et al. 2022: fig. 11); Xenopeltis unicolor : 187-190 trunk and cloacal vertebrae plus 26-?30 caudal vertebrae ( Alexander and Gans 1966); Xenopeltis unicolor : 188 trunk vertebrae plus 34 cloacal and caudal vertebrae ( Nopcsa 1923); Xenopeltis unicolor : 188 trunk vertebrae plus 30 cloacal and caudal vertebrae ( Polly et al. 2001); Xenopeltis unicolor : 187 trunk and cloacal vertebrae plus unknown number of caudal vertebrae ( Gasc 1974); Xenopeltis unicolor : 183 trunk vertebrae plus 7 cloacal vertebrae (apparently erroneous) plus 20 caudal vertebrae ( Rochebrune 1881); Xenopeltis unicolor : 188-210 vertebrae in total ( Romer 1956); Xenopeltis unicolor : 181 trunk vertebrae plus unknown number of cloacal and caudal vertebrae ( Tsuihiji et al. 2012).