Oxyrhopus occipitalis (Wagler)

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 : 488-490

Oxyrhopus occipitalis (Wagler)

Taxonomic history

Oxyrhopus occipitalis was originally described from Rio Solimõens, Amazonas, Brazil ( Hoogmoed & Gruber, 1983). Bailey (1970) synonymised O. occipitalis with O. formosus , despite his stated belief that the latter consists of a complex of species. Oxyrhopus occipitalis was revalidated by Hoge et al. (1973).

Oxyrhopus occipitalis differs from O. formosus by its slender body form (more robust in O. formosus ), snout yellow and top of head brown (entire head yellow or cream), adults red with very faint body bands (adults with prominent black bands)( Table 2).

Of the two species, only O. occipitalis occurs in the Guiana Shield. All of the Oxyrhopus from the Guiana region that have been identified as O. formosus are actually O. occipitalis . We include O. formosus in Table 2 only to summarise differences between it and O. occipitalis .

Material examined – two males, one female (Appendix).

Morphology

Maximum total length in our sample is 573 mm; maximum reported length is 996 mm (Hoge et al., 1973). Lower labials 7-10, five in contact with shields; preoculars 1; postoculars 2. Tail length 21-23% of total length in males, 19% in female. Measurements are in Table 1.

Colour and Pattern

Dorsal ground colour red or reddish orange; snout and supralabials yellow; top of head medium to dark brown. A white anterior body band (sometimes obscure), 3-4 dorsal scales in width, approximately 2 cm behind the head. Faint, pale orange body bands with very narrow dark borders; width of pale orange bands equal to the length of 2-4 dorsal scales. Bands are usually symmetrical, but in one specimen there is a half-band, on one side only, between otherwise symmetrical bands. Bands on body 15-17, on tail 5-6. Underside of head yellowish orange. Venter white; dorsal pigment barely touches the edges of some ventrals. Underside of tail banded orange and white, corresponding to dorsal pale orange bands and red ground respectively ( Fig. 1 A-C).

There is considerable ontogenetic change in colour pattern. In most cases bands are prominent in juveniles but become inconspicuous in adults (Martins & Oliveira, 1999). However, a juvenile with the typical adult pattern of inconspicuous bands has been reported from southern Venezuela (C.L. Barrio-Amorós, pers. comm.). Bands are often more visible in preservative, less conspicuous on living specimens. Photographs are in Starace (1998 [as O. formosus ]), Martins & Oliveira (1999 [as O. formosus ]) and Campbell & Lamar (2004).

Distribution in the Guiana Shield

Because Oxyrhopus occipitalis has been confused with O. formosus , reports of the latter species in the Guiana Shield region must be discounted. There are no confirmed records of O. formosus in the Guiana Shield region. Oxyrhopus occipitalis has been reported from Amazonas, Brazil ( Jorge da Silva & Sites, 1995), Amapá, Brazil ( Avila-Pires, 2005 [as O. formosus ]), Amazonas, Venezuela ( McDiarmid & Paolillo, 1988 [as O. formosus ]), Bolívar, Venezuela ( Mattei & Barrio, 1999 [as O. formosus ]), Surinam ( Avila-Pires, 2005 [as O. formosus ]) and French Guiana ( Gasc & Rodrigues, 1980; Chippaux, 1986; Starace, 1998 [as O. formosus ]).

This paper reports the first records of O. occipitalis from Guyana. Specimens were collected in forest; habitat description is in Ernst et al. (2005) and Kok & Kalamandeen (2008). Distribution in Guyana is mapped in Fig. 2 .

Figures

FIGURE 1: Oxyrhopus occipitalis and O. melanogenys from Guyana: A. Dorsolateral view of O. occipitalis (IRSNB 17913) in life (photo by PJRK), B. Ventral view of O. occipitalis (IRSNB 17913) in life (photo by PJRK), C. Dorsolateral view of O. occipitalis (SMNS 12111) in life (photo by RE), D. Dorsolateral view of O. melanogenys (CSBD HR 700) in life (photo by D.B. Means).

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.