Alsophis sp. 2, Fitzinger, 1843

Bochaton, Corentin, Boistel, Renaud, Grouard, Sandrine, Ineich, Ivan, Tresset, Anne & Bailon, Salvador, 2019, Fossil dipsadid snakes from the Guadeloupe Islands (French West-Indies) and their interactions with past human populations, Geodiversitas 41 (12), pp. 501-523 : 512

Alsophis sp. 2

EXAMINED MATERIAL. — A total of 51 bones, all trunk vertebrae, from 11 sites on all islands except Petite-Terre (see Table 1 ) are attributed to an unknown species of the genus Alsophis .

DESCRIPTION

Trunk vertebrae (51 elements; Fig. 6A)

These vertebrae are of intermediate size, with centra lengths between 2.7 and 4.4 mm. In dorsal view, their proportions range from short and slightly wider than long to slightly longer than wide (CL/WIC = 0.86-1.15) and consistently exhibit a strong medial constriction. Still in dorsal view, the zygosphene is wide with a slightly trilobate anterior margin, the prezygapophyseal facets are ovoid, and the prezygapophyseal processes are conical and elongate (1.5 longer than wide) with a blunted distal end. In lateral view, the neural spine is clearly higher than long and has vertical anterior and posterior margins. The hemal keel is more extended ventrally than in fossil trunk vertebrae of A. antillensis and has a straight ventral margin becoming shallower anteriorly. The hemal keel does not reach the sub-cotylar ring and it forms a distinct step under the posterior limit of the diapophysis. In ventral view, the hemal keel is laterally well-delimited, thin, and is more or less spatulate in shape (sensu Holman 2000) with a posterior enlargement of variable extent. In anterior view, the cotyle is small, deep, and circular. It is laterally bordered by paracotylar foramina and deep paracotylar depressions. In posterior view, the neural arch is strongly vaulted and thicker than in the other studied fossil dipsadid snakes, and the condyle is small and circular. In ventral view, the centrum is triangular and its anterior part bears well-marked subcentral ridges and deep subcentral grooves.

REMARKS

These fossil vertebrae exhibits significant differences relative to those attributed to Alsophis antillensis : they are shorter with a stronger medial constriction in dorsal view; the neural spine is higher and shorter in lateral view, with straighter anterior and posterior margins; well-marked subcentral ridges are visible in lateral view; the cotyle is small and circular in anterior view; and the neural arch is thicker and more vaulted in posterior view. We observed all these characteristics in modern Alsophis rufiventris trunk vertebrae, a snake occurring in Saba and possibly extinct in Saint-Christopher banks ( Powell & Henderson 2012), which conservatively indicates that our fossil snake was part of the genus Alsophis . Similar vertebrae were identified as Colubroidea sp. 2 or Dipsadidae sp. 2 in previous studies ( Bochaton et al. 2015; Bailon et al. 2015). However, comparative specimens are too scarce for us to confidently attribute these 51 vertebrae to A. rufiventris . Instead, we assign these specimens to an unknown and extinct species of Alsophis that was morphologically close to Alsophis rufiventris , a species known to have occurred at least 120 km north of the Guadeloupe Islands. Fossil vertebrae exhibiting a similarly short centrum and high neural spine were described by Auffenberg (1958) on Barbuda and attributed to the genus Clelia . Unfortunately, Auffenberg (op. cit.) never figured these vertebrae and his material is not available in the collections of the Florida Museum of Natural History. We believe it is likely that the vertebrae described by Auffenberg were similar to the ones we describe here and thus propose his material so that they also can be referred to the genus Alsophis . A gross size comparison with modern Alsophis specimens shows that fossil vertebrae from the Guadeloupe Islands correspond to individuals between 75 and 120 cm in total length.