Arrhyton Günther, 1858

Syromyatnikova, Elena, Aranda, Ernesto & González, Soraida Fiol, 2021, First insight into the diversity of snakes in the Pleistocene of Cuba, Acta Palaeontologica Polonica 66 (2), pp. 395-407 : 400

publication ID	https://doi.org/ 10.4202/app.00766.2020
persistent identifier	https://treatment.plazi.org/id/03D187E2-3E1C-FF8F-C36C-F963FD09FA03
treatment provided by	Felipe
scientific name	Arrhyton Günther, 1858
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Genus Arrhyton Günther, 1858 View in CoL

Type species: Arrhyton taeniatum Günther, 1858 ; Recent of Cuba .

Arrhyton sp.

Fig. 4A View Fig .

Material.—13 precloacal vertebrae ( PIN 5782/23–35), V and VII layers, late Pleistocene, El Abrón Cave, Cuba.

Description.—The vertebrae are small, with a centrum length ranging 1.6–2.2 mm ( Fig. 4A View Fig ; PIN 5782/23). They are slightly longer than wide (ratio CL/NAW is 1.1). In dorsal view, the interzygapophyseal constriction is moderately developed and anteroposteriorly short, positioned close to the prezygapophyseal facets ( Fig. 4A View Fig 1 View Fig ). The neural spine is thickened along its dorsal edge, sometimes with an indistinct bifurcation at its anterior tip. Posteriorly, the thickening of the neural spine is slightly decreased, and the posterior tip of the spine is pointed. The zygosphene is clearly three-lobed in dorsal view. Posteriorly, the neural arch bears a wide triangular notch. The prezygapophyseal facets are elongate in outline. The prezygapophyseal processes are relatively small, rounded at the tips, and anterolaterally oriented. They do not extend beyond the level of the prezygapophyseal facets in dorsal view. In some specimens the prezygapophyseal processes tend to be the conical shaped. In ventral view, the haemal keel is spatulate shaped, and can be more or less widened ( Fig. 4A View Fig 2 View Fig ). The subcentral area is relatively narrow and slightly concave ventrally. The subcentral ridges are poorly developed. The subcentral foramina are present, but small. In lateral view, the neural spine is longer than high ( Fig. 4A View Fig 3 View Fig ). Its anterior end is somewhat sloping and slightly overhangs anteriorly, whereas the posterior end is acute and has a stronger overhang posteriorly. The haemal keel is clearly visible in lateral view, and its ventral margin is straight. The synapophyses are massive, clearly separated into diapophyses and parapophyses, the latter located more posteriorly. The lateral foramina are relatively large, about twice the size of the subcentral foramina. In anterior view, the neural canal is large and wide, being higher and wider than the cotyle ( Fig. 4A 4 View Fig ). The zygosphene is distinctly convex dorsally with the shape of an inverted “ V ”. The cotyle is deep and slightly flattened dorsoventrally. The prezygapophyseal facets are approximately horizontal. The paracotylar foramina are present. In some specimens a pair of relatively large foramina are positioned above the paracotylar foramina. In posterior view, the neural arch is vaulted, with a triangular shape ( Fig. 4A View Fig 5 View Fig ). The neural canal is large and wide, as in anterior view, and is higher and wider than the condyle. At the bottom the neural canal is markedly widened, looking tetragonal in outline. The condyle is circular in shape.

Remarks.—The described vertebrae can be assigned to Dipsadidae based on relatively elongated centrum, presence of haemal keel instead of hypapophysis, and synapophyses clearly divided into diapophyses and parapophyses ( Holman 1979, 1981, 2000). The vertebrae described from El Abrón Cave are relatively small and correspond in size to species of Arrhyton , showing SVL <450 mm. It is also similar to species of Arrhyton in general proportions, and the shape of the prezygapophyseal processes and zygosphene (EVS, personal observation based on the Recent species Arrhyton taeniatum, PIN H 101). Arrhyton has eight species which are endemic to Cuba ( Powell and Henderson 2012). According to Rodríguez-Schettino et al. (2013), only two species ( A. taeniatum and A. vittatum ) are widely distributed in Cuba, including the Pinar del Río Province. The species of Arrhyton from El Abrón Cave differs from Arrhyton vittatum in having a higher neural spine and moderately vaulted triangular neural arch (EVS, personal observation based on the specimen Arrhyton vittatum (Gundlach in Peters, 1861), PIN H 102). Comparison with other species of Arrhyton from El Abrón Cave was not possible given the limited available sample of Recent specimens. Because no osteological characteristics are provided for Arrhyton , we assign the described specimens to Arrhyton sp.