Oxyrhopus petola (Linnaeus)

MacCulloch 1, Ross D., Kok, Philippe J. R., Ernst, Raffael & Kalamandeen, Michelle, 2009, The genus OXYRHOPUS (Serpentes: Dipsadidae: Xenodontinae) in Guyana: morphology, distributions and comments on taxonomy, Papéis Avulsos de Zoologia 49 (36), pp. 487-495 : 491-494

Oxyrhopus petola (Linnaeus)

Taxonomic history

Oxyrhopus petola has a very large range, occurring from Mexico to Bolivia. Several subspecies have been described, usually based on colour pattern ( Bailey, 1970). Chippaux (1986) expressed doubts about the criteria used to define the subspecies, stating that O. petola might be a highly variable taxon, or a complex of species.

Material examined – four males, one female, one juvenile (Appendix).

Morphology

Maximum total length in our sample is 1048 mm, maximum reported length is 1100 mm ( Moonen et al., 1979). Lower labials 10, six in contact with shields; preocular 1; postoculars 2. Measurements of adults are in Table 1. The juvenile measures 196 mm SVL, tail 60 mm, ventrals 214, subcaudal pairs 95. Relative tail length in 22-24% in males, 17% in the female, 24% in the juvenile.

Colour and Pattern

Terminology used to describe the colour pattern of Oxyrhopus petola has been inconsistent. Beebe (1946) and Abuys (1985) describe the pattern as red bands on a black ground; Roze (1966), Chippaux (1986) and Starace (1998) describe the pattern as alternating black and red bands; Bailey (1970) and Kornacker (1999) describe the species as having black bands with red interspaces. We follow the latter in the interest of consistency within the genus Oxyrhopus , in which the arrangement of black bands is often diagnostic.

Relative widths of bands and interspaces are variable. Bailey (1970) stated that in Oxyrhopus petola from northern South America “…[black] bands [are] approximately equal in length, separated by interspaces about one scale wide”. In specimens from French Guiana and Venezuela the interspaces are approximately equal in size to the black bands ( Roze, 1966; Chippaux, 1986; Starace, 1998; Kornacker, 1999). Abuys (1985) showed a photo of an individual with very narrow and asymmetrical interspaces, and stated that interspace width is variable in specimens from Surinam. The bands are wider than the interspaces in an individual from Surinam photographed by Moonen et al. (1979). In some individuals very narrow white bands are present between the black bands and the red interspaces ( Beebe, 1946; Kornacker, 1999). Melanism was reported by Abuys (1985) and Chippaux (1986). Esqueda et al. (2007) reported partial albinism in a specimen from Venezuela.

In specimens from Guyana the interspaces are red or reddish brown and the black bands are approximately 2X the width of the interspaces (bands 3-6 scales in width, interspaces 1-3 scales). Bands and interspaces may be asymmetrical. Venter whitish, immaculate, with dorsal black bands contacting the outer ends of the ventrals ( Fig. 4 ).

Distribution in the Guiana Shield

Oxyrhopus petola is found throughout the Guiana Shield, except Delta Amacuro, Venezuela ( Roze, 1966; Bailey, 1970; Chippaux, 1986; Starace, 1998; Kornacker, 1999; Avila-Pires, 2005; Donnelly et al., 2005). More detailed distribution records have been reported by several authors, from habitats ranging from forest to savannah to towns ( Beebe, 1946; Roze, 1966; Moonen et al., 1979; Abuys, 1985; Starace, 1998; Gorzula & Señaris, 1999). Fig. 2 shows distribution in Guyana.

Remarks

Although some recent work has contributed to the understanding of the systematics and distributions of Oxyrhopus , species identifications can still be problematic. Some widespread taxa, such as O. formosus , O. melanogenys and O. petola , may contain more than one species. Further study using morphological and molecular methods will be necessary to determine this.

Figures

FIGURE 2: Distribution of Oxyrhopus in Guyana. Stars = O. occipitalis; circles = O. melanogenys; squares = O. petola. Locations are from Donnelly et al. (2005), Means & Kalamandeen (2007), MacCulloch & Lathrop (2009) and the Appendix.

FIGURE 4: Preserved Oxyrhopus petola from Guyana: A. Dorsal view of CSBD HR 89, B. Ventral view of CSBD HR 89 (photos by MK).