Uropeltidae Mueller , 1831, 1828

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

Uropeltidae Mueller, 1831

General information.

Uropeltids are a moderately diverse family of fossorial snakes, with more than 60 species, currently endemic to India and Sri Lanka ( Wallach et al. 2014; Pyron et al. 2016; Boundy 2021; Sampaio et al. 2023). They are characterized by a large external keratinous shield on their tails ( Pyron et al. 2016; Huntley et al. 2021), hence their common name as “shield-tailed” snakes (or simply “shieldtails”) and their etymology (from the Greek “οὐρά” meaning “tail” and “πέλτη” meaning “shield”). This is a very old lineage, with divergence dates suggesting that uropeltids split from other uropeltoids already by around the Paleocene-Eocene boundary ( Cyriac and Kodandaramaiah 2017).

In terms of their vertebral morphology, Uropeltidae primarily differ from all other snakes (and actually all other amniotes) by their unique peculiar morphology of the atlas-axis complex, i.e., the axis articulates directly with the occipital condyle (for details see Baumeister 1908; Williams 1959; Hoffstetter and Gasc 1969; Rieppel 1979; Pyron et al. 2016; and references therein). As for the succeeding vertebrae, all uropeltid genera for which complete (or almost complete) axial skeletons were available display highly homogenous morphology of individual vertebrae as well as exactly the same pattern of intracolumnar variation. This is described in detail below for Brachyophidium . In general, vertebrae of uropeltids are characterized by an elongate centrum, depressed cotyle and condyle, a strongly concave zygosphene in dorsal view, high-angled prezygapophyses (an average of>24°), depressed neural arch, absent or very shallow concave posterior median notch of the neural arch, absent haemal keels in mid- and posterior trunk vertebrae, vestigial (or absent) neural spine posteriorly restricted resulting in a saddle-shaped dorsal margin of the neural arch, presence of prominent hypapophyses throughout the cloacal and caudal portions, and (most usually) a very low number of caudal vertebrae (for more details see Description and figures below).

Moreover, exactly beneath the scales of the characteristic external tail shield of uropeltids, there lies a peculiar bone structure which is fused to the termination of the posteriormost few fused caudal vertebrae ( Baumeister 1908; Huntley et al. 2021). This internal osteological structure was referred by Huntley et al. (2021) as the "bony tail-shield".

Previous figures of vertebrae of extant Uropeltidae have been so far presented by Baumeister (1908), Williams (1959), Hoffstetter and Gasc (1969), Dowling and Duellman (1978), Garberoglio et al. (2019), Palci et al. (2020), Head (2021), Ganesh et al. (2022), and Alfonso-Rojas et al. (2023). Among these, vertebrae from the cloacal and/or caudal series were presented by Baumeister (1908), Hoffstetter and Gasc (1969), Palci et al. (2020), and in a μCT image of a whole skeleton in Ganesh et al. (2022). Quantitative studies on the intracolumnar variability of uropeltid vertebrae were conducted by Hoffstetter and Gasc (1969), Gasc (1974), and Head (2021). Beyond these, brief descriptions and observations of uropeltid vertebrae had been done already by the 19th century ( Peters 1861). Hoffstetter (1968) observed that hypapophyses in Rhinophis blythii reappear before the cloaca. Before, Underwood (1967) reported erroneously the absence of hypapophyses behind the cervical portion of the column in Uropeltis and supposed that this condition may be characteristic for the whole family. More recent descriptions (without figures) of vertebral features of uropeltids were provided by Smith (2013).

We here studied individuals of multiple species of Brachyophidium Wall, 1921, Melanophidium Günther, 1864, Platyplectrurus Günther, 1868, Plectrurus Duméril & Duméril, 1851, Rhinophis Hemprich, 1820, Teretrurus Beddome, 1886, and Uropeltis Cuvier, 1829, which correspond to all extant genera (note that in some recent taxonomic schemes, Teretrurus is considered a senior synonym of Brachyophidium ; Ganesh and Murthy 2022; Sampaio et al. 2023).