Vanzosaura rubricauda (Boulenger, 1902)

Gymnophthalmus rubricauda: Boulenger, 1902, p. 24.

Vanzosaura rubricauda: Rodrigues, 1991, p. 340.

Holotype: BMNH 1946.8.2, from the municipality of Cruz del Eje, province of Córdoba, Argentina.

Diagnosis: Vanzosaura rubricauda is characterized by: (1) 27–43 smooth subcaudals; (2) 12–16 femoral pores in males; (3) snout round in profile; (4) forelimbs proportionally short in relation to trunk length, with FAL 54.8 ± 0.02% of TRL in females and 57.5 ± 0.02% in males; (5) colour pattern variable, ranging from no stripes to 12 whitish dorsal stripes, which become irregular or discontinuous on the head; (6) inner ventral row of scales slightly narrower or subequal in relation to the external scales; (7) prefrontal scales usually separated (89%); (8) medium to large size for the genus, with the largest male attaining an SVL of 36.0 mm and the largest female attaining an SVL of 41.5 mm; (9) proportionally short tails for the genus, with an average rate of complete tails (not regenerated) in relation to body size (TAL/ SVL) of 1.51 ± 0.14.

Variation: As noted for the other species, the sexes are dimorphic in size, with females having a larger SVL (ANOVA; F 1,221 = 52.06, P <0.01) and a larger TRL (ANCOVA, F 1,228 = 40.80, P <0.01), whereas males have longer FEM (F 1,228 = 85.21, P <0.01) and HW (F 1,228 = 33.80, P <0.01). Populations from the western Cerrado of Brazil and Paraguay are distinct from Chaco populations in having smaller body sizes (ANOVA; females, F 1,98 = 17.63, P <0.01; males, F 1,120 = 27.50, P <0.01), proportionally longer tails (ANCOVA; F 1,54 = 9.27, P <0.01), and fewer ventrals (Mann– Withney, U 1,132 = 1256.5, P <0.05). Nevertheless, morphological differences are subtle, and individuals from both regions cannot be readily distinguished based on the meristic data used in this study. The Chaco populations are also locally variable, with some individuals having contact between the prefrontals (19%), a condition that is not observed in the western Cerrado populations (Fig. 4), and presenting polymorphism in colour pattern in a population from the province of Santa Cruz, Bolivia, a condition that is only observed in populations of V. multiscutata comb. nov. from the Caatinga (Fig. 5).

Distribution and natural history: Vanzosaura rubricauda occurs along the Dry Chaco region of Argentina, Paraguay, and Bolivia, and in the Cerrado region of eastern Paraguay and western Brazil in the states of Mato Grosso, Mato Grosso do Sul, and Goiás (Fig. 10). In the province of Salta, in the Chaco region of Argentina, annual activity and reproduction is highly seasonal, with individuals being found in the hottest months (Cruz, 1994). The species is found in open formations, and in the Cerrado region it is found almost exclusively in savannah and grassland in regions with sandy soils (Nogueira, 2006; Valdujo et al., 2009).

Remarks: The holotype of V. rubricauda is currently in bad condition (P. Nunes, pers. comm.). Nevertheless, it preserves characters that are still useful to recognize the species. A well-preserved specimen from Cruz del Eje (MACN 12504), close to the type locality, is housed in the Museo Nacional de Ciencias Naturales ‘ Bernardino Rivadavia’ in Buenos Aires, Argentina.