Arrhyton Günther, 1858

Hedges, Blair, Couloux, Arnaud & Vidal, Nicolas, 2009, Molecular phylogeny, classification, and biogeography of West Indian racer snakes of the Tribe Alsophiini (Squamata, Dipsadidae, Xenodontinae), Zootaxa 2067, pp. 1-28 : 20

Genus Arrhyton Günther, 1858

Type species. Arrhyton taeniatum Günther, 1858:244 .

Diagnosis. See diagnosis for the subtribe Arrhytonina.

Content. Eight species are included in the genus ( Table 1).

Distribution. The genus is distributed throughout Cuba ( Fig. 2 ).

Remarks. Species of Arrhyton ( Fig. 3 G) are small (448 mm, maximum SVL) racers. An informal classification of Cuban Arrhyton was based on color pattern and scalation, especially ventral and subcaudal counts ( Schwartz & Garrido 1981; Hedges & Garrido 1992). The most distinct species, morphologically, is A. taeniatum , because it lacks a loreal scale, has an enlarged rostral (presumably related to semi-fossorial habits), and has a boldly striped pattern. It was placed in its own species group ( taeniatum Group) and the sequence evidence ( Figs. 1 and 4 ), although missing A. ainictum , shows it to be the sister group of all other species of Arrhyton . The three species having high ventral scale counts and long tails ( A. dolichura , A. procerum , and A. tanyplectum ), were placed together in the dolichura Group, also supported by DNA evidence ( Fig. 1 ). The remaining species, with lower ventral counts and relatively short tails, were placed in a separate group, the vittatum Group, though this is resolved (without maximal support) as paraphyletic in our phylogeny.

Figures

FIGURE 2. Map showing the West Indies (including the southern tip of Florida above, Central America to the west, and the northern edge of South America below) and the distributions of the genera of the Tribe Alsophiini, Subfamily Xenodontinae, Family Dipsadidae.

FIGURE 3. Representatives of genera of the snake Tribe Alsophiini (Dipsadidae: Xenonodontinae). Subtribe Alsophiina: Alsophis manselli (Woodlands Spring, Montserrat), Borikenophis portoricensis (1.5 km W. Playa de Tamarindo, Puerto Rico), Cubophis cantherigerus (2.0 km W Viñales, Pinar del Rio, Cuba), Hypsirhynchus ferox (Barahona, Barahona, Dominican Republic), Ialtris dorsalis (3 km N Bois Sec, Grand’Anse, Haiti), and Magliophis stahli (1.9 km NE Vista Alegre, Puerto Rico). Subtribe Arrhytonina: Arrhyton taeniatum (0.2 km WE Windmill Beach, Guantanamo Bay Naval Station, Cuba). Subtribe Uromacerina: Uromacer oxyrhynchus (4.4 km W Canada Honda, La Altagracia, Dominican Republic). Photos by S. B. Hedges.

FIGURE 1. A phylogeny of Alsophiini. Bayesian tree obtained from the combined data set of six genes (RAG 2, 12 S & 16 S rRNA, cytochrome b, ND 2 and ND 4; 3387 sites). Alsophis portoricensis portoricensis and A. p. anegadae have identical sequences at all genes sampled, and therefore the latter taxon is not shown. Values are ML bootstrap values above 70 % followed by Bayesian posterior probabilities above 90 %. The generic taxonomy in this tree reflects usage prior to this study and shows paraphyly and polyphyly of Alsophis (blue), Arrhyton (purple), and Antillophis (orange). See Table 1 and Figure 4 for the new classification proposed here.

FIGURE 4. A timetree of Alsophiini. Divergence times and credibility / confidence intervals are shown in Table 3. Plei = Pleistocene. The generic taxonomy in this tree reflects the new classification proposed here and detailed in Table 1.