Rhinocerophis jonathani

Results

External morphology. The new specimens share characters of lepidosis originally used to diagnose this species from other pitvipers ( Harvey, 1994): in all specimens, the prelacunals and 2nd supralabials are discrete; all specimens have high numbers of supralabials, intersupraoculars and dorsals ( Fig. 2 View FIGURE 2 ).

Largest specimen (SVL 800 mm), an adult female (MNKR 1618) already examined by Harvey et al. (2005); smallest specimen (SVL 280 mm), a female juvenile (CBF 2673); among remaining specimens, SVL 380–590 mm (528 ± 203, n = 3) in females and 430– 90 mm (567.8 ± 90.8, n = 7) in males; TL 45–90 mm (62.2 ± 24.8, n = 3) in females and 60–90 mm (76.7 ± 14, n = 7) in males; in males, TL/SVL 0.1–0.2 (0.1 ± 0.02, n = 6), in females, TL/SVL 0.1–0.2 (0.1 ± 0.02, n = 4); head (measured from the neck to the tip of the snout) 5–7% (6 ± 1, n = 12) of SVL; eye-nostril distance (measured from the anterior border of the orbit to the center of the naris) accounts for 27–33% (29 ± 2, n = 12) of head length; interorbital distance (measured between posterior margins of orbits) is 54–74% (62 ± 6, n = 11) of head width (measured at level of rictus); internasal distance (measured between nares) is 22–33% (27 ± 4, n = 11) of head width; ventrals 163–168 (165.4 ± 1.9, n = 5) in females and 156–168 (162.6 ± 4.8, n = 7) in males; subcaudals 34–41 (38.6 ± 3.6, n = 5) in females and 39–41 in males (38.4 ± 5.1, n = 7).

Ventral counts and relative tail lengths are not sexually dimorphic (t = -1.031, df = 9, P = 0.329; t = 2.18, df=9, P = 0.056; respectively). The high probability that male and female subcaudal counts are the same (t = 1.14, df = 9, P = 0.283) suggests that these counts are also not dimorphic. However, our sample sizes are small and we did not consider the power of our t -test for these traits.

Dorsals 26–29 (27.4 ± 1.9, n = 12) one head length behind rictus, 27–30 (27.8 ± 1.4, n = 12) at midbody, and 19–22 (21.2 ± 2.9, n = 12) one head-length before cloaca; three preocular scales contacting orbit; inferior preocular small and completely or partially fused with sublacunal (58%, n = 12) or discrete (42%, n = 12); superior preocular contributing to canthus and divided in 50% (n = 12) specimens. Suboculars 2–4 (3.1 ± 0.8, n = 12), postoculars 2–4 (2.7 ± 0.6, n = 12), supralabials 9–12 (10.6 ± 1, n = 12), infralabials 12–15 (13.5 ± 0.8, n = 12), gulars 5–6 (6.6 ± 0.8, n = 11), interoculabials 4–6 (4.8 ± 0.5, n = 12). Supralacunal divided in 33% (n = 12) of specimens; sublacunal divided in two portions in 58% (n = 12) or divided into three portions in 42% (n = 12) of specimens; prelacunal separated from supralabials by subfoveals in complete row except in MNKR 2036 and CBGR 65 in which sublacunal contacts supralabials (incomplete row of subfoveals). Postfoveals 2–8 (3.7 ± 2.2, n = 12); prefoveals 4–15 (7.4 ± 3.5, n = 12) separating prelacunal from postnasal. Loreal not elongated (as high as wide) (MNKR 718, MNKR 1618, CBGR 65, CBF 2673, MHNC-R 206, MHNCR 207, FML 1050) or elongated (rectangular) (MNKR 2036, CBF 2318, CBF 2319, CBF 2320, FML 570); rostral trapezoidal and as broad as high; internasals in contact; intercanthals 5–9 (6.2 ± 1.1, n = 12); intersupraoculars 9–14 (10.9 ± 1.4, n = 12); scales around supraoculars 9–11 (9.7 ± 1.1, n = 11); right supraocular divided in CBF 2318; canthals 1/1 (70%, n = 13) or 2/2 (30%, n = 13). Interrictals, counted in straight line between last supralabials and including them, 30–36 (32.7 ± 1.7, n = 12). Terminal spine extending for 4–9 mm on the tail.

Coloration. In general, coloration of the new specimens resembles that of the types ( Harvey, 1994). Nonetheless, we note variation in several features ( Fig. 3 View FIGURE 3 ). The dorsal blotches are rectangular, subtriangular or C-shaped, and this can vary even in the same specimen. The dorsal blotches may be fused in the vertebral region. Some specimens (CBF 2673, CBGR 65) have rounded spots between blotches. Tip of tail of juvenile (CBF 2673) same color and pattern as proximal tail. Ventrally, a dark stripe starts on the first ventral scales, extends posteriorly along the anterior part of the body and then becomes diffused in several bands of dark spots. This stripe is longer in FML 1050 and is absent in CBF 2673 and MNKR 1618. The postocular stripe is 4–6 scales wide (at the 5th–6th supralabials) and can enclose the rictus (FML 1050, CBF 2318, CBF 2673, MNHC-R 206, MNKR 1618, MNKR 2036) or extend posteriorly without enclosing it (FML 570, MNHC-R 207, CBF 2320, MNKR 718). In most specimens, the antero-ventral corners of the first few supralabials are dark tan. However, in FML 1050 and FML 570, the first supralabials are pigmented with diffuse dark spots, as observed in some specimens of Rhinocerophis alternatus . The cephalic ground coloration is dark tan. A white stripe extends between the supraoculars and, posteriorly, the pattern tends to be formed by two white lateral stripes that join with a central one. Figure 3 View FIGURE 3 illustrates variation in cephalic striping.

Cranial osteology. Nasals slightly curve downwards ( Fig. 4 View FIGURE 4 , 5 View FIGURE 5 ), extending ventrally to form internasal septum, which continues premaxillary plate; nasals posteroventrally joining frontals and dorsally attaching to them with ligaments. Frontals quadrangular, slightly longer than wide with elevated lateral margins. Parietal quadrangular, slightly wider than long, its width at anterior end of supratemporals greater than minimum width across frontals; parietal possessing pair of lateral expansions where postfrontals (= postorbitals) articulate; posterolateral-dorsal margins of parietal concave, its concavity more accentuated in MNKR 1618 and CBF 2319 than in other specimens.

Shape of postfrontals variable: elongate and contacting frontals in MNKR 1618, but not in CBGR 65, CBF 2319 and FML 1408 in which postfrontals contribute more to orbit border than parietal; in MHNC-R 206, postfrontals reduced, not contacting frontals and contributing equal to or less than parietal to orbit. Supratemporals elongate and flattened, located in longitudinal dorsal depressions of prootics, slightly expanded proximally and possessing two lateral expansions distally (internal expansion greater than external); supratemporals articulating with quadrates posteriorly. Quadrates elongate and flattened, slightly expanded; ventral process of quadrate oval and conspicuous, articulating with columella auris, more developed in MNKR 1618 and CBF 2319 than in other specimens; quadrates articulating with pterygoid and mandible.

Supraoccipital with pair of crests extending from antero-medial portion to posterolateral edges; crests accentuated and almost in contact with parietal in MNKR 1618 and CBF 2319, but less accentuated and separated from parietal in other specimens. Exoccipitals in medial contact with supraoccipital, delimiting foramen magnum with basioccipital and forming occipital condyle. Basioccipital with medial crest continuous with longitudinal crest of basisphenoid crest; basioccipital crest well developed, except in CBF 2319 and MHNC-R 206. Prootic articulating with supratemporal; perforated laterally by two foramina, presumably for the maxillary and mandibular branches of the trigeminal nerve (for an explanation of the correspondence between cranial foramina and cranial nerves, see Romer, 1956; Liem et al. 1971; Moro, 1996; Zanella & De Lema, 1999); foramina separated by bony partion. Anteriorly, basisphenoid triangular; its margins with well developed lateral expansions; medial crest running length of basisphenoid; crest uniformily elevated in CBF 2319, with rounded central projection in other specimens; elongate depressions present on either side of crest; posterior portion of basiphenoid with four foramina, corresponding presumably to the cerebral artery and Vidian foramina.

Premaxilla single, with inverted T shape, its posterior portion forming thin plate between nasals; premaxilla articulating with vomers and the septomaxilla ventrally. Septomaxilla contributing to olfactory capsule, positioned between vomers and premaxilla. Vomer with thin lateral expansions directed upward; each vomer bearing fenestra for Jacobson’s organ.

Prefrontal contributing to orbit, quadrangular and irregular in ventral aspect, its dorsal surface rectangular and concave; internal process of prefrontal articulating with frontal; external process of prefrontal continuing internally and ventrally contacting maxillary crest; anterior process of prefrontal articulating with ascendant process of maxilla.

Maxilla supporting functional fang and bearing 3–5 loosely attached replacement fangs; internal crest of maxilla well developed (except in CBF 2319) perforated by a foramen probably for maxillary branch of trigeminal nerve; center of maxilla cup-shaped, its posterior margin articulating with ectopterygoid and anteriorly, ascendant process forming condyle for articulation with prefrontal. Ectopterygoid elongate, articulating anteriorly with maxilla, thin throughout its anterior one-third then curving and convex posteriorly; anterior end of ectopterygoid forked, its external fork longer than its internal fork; posterior extremity of ectopterygoid small and contacting pterygoid. Palatine contacting prefrontal and pterygoids, bearing 2–3 teeth and an anterodorsal, triangular process. Pterygoids articulating with palatine and mandible anteriorly, with quadrate and ectopterygoid posteriorly; anterior portion of pterygoid thin, straight, bearing 9–12 teeth, and with small depression for articulation with ectopterygoid; posterior end of pterygoid expanded into rounded and symmetric crest.

Mandibles formed by compound bone ( Kamal & Hammouda, 1968), angular-splenial, and dentary ( Fig. 6 View FIGURE 6 ). Meckelian fossa with rounded, symmetric crest located medially in the compound bone. Angular and splenial fused into single bone bifurcating anteriorly, inferior branch longer than superior one; branches of angular-splenial enclosing Meckel‘s groove internal to dentary. Dentary with 10–12 sharp and curved teeth; mental foramina opening on external face of dentary.

Hemipenis. Hemipenis bilobed ( Fig. 7 View FIGURE 7 ). Hemipenes everted are 15–22.9 mm total length, and 20–28 % of caudal length; hemipenial lobes parallel with each other and subcylindrical; hemipenial body 50–67% of total hemipenial length; capitulum longer on sulcate side, occupying 60–80% of lobe; base of capitulum covered in spinulate (0.1–0.2 mm long) calyces (MNKR 718, CBGR 65, CBF 2320) or calyces lacking spinules (MHNC-R 206, FML 1050); 30–40 hook-shaped spines (1.4–2.1 mm long) distributed asymmetrically on lobes, denser on sulcate side; smaller, thinner and curved spines (0.9–1.5 mm long) present in intralobular region; hemipenial body, margins of sulcus spermaticus, and intrasulcar region covered in spinules (0.1–0.4 mm long); sulcus spermaticus bifurcating proximal to capitulum, its branches extending distally to tips of lobes; lateral surface of hemipenial body with longitudinal depression (63–72% of body length); asulcate surface of hemipenial body with a conspicuous protuberance located medially.

Distribution and ecological notes. One specimen collected in Curqui (CBF 2320) was resting in a rock crevice in the shade of a tree ( Prosopis ferox ), and another individual (CBF 2318) was found moving across open ground. Before and during capture, both specimens rapidly vibrated their tails, in one instance striking dry leaves and resembling the sounds made by rattlesnake (a behavior we also observed in Rhinocerophis alternatus , R. ammodytoides and Bothropoides diporus ). Of the specimens collected in Quebrada de Loray, one (MHNC-R 206) was found resting in an open rocky area and the other (MHNC-R 207) was found climbing a steep ravine covered by Acacia , Schinus and Alnus . The specimen photographed in Padcaya ( Fig. 1 View FIGURE 1 ) was found resting on a rocky shelf of a shrub-covered slope. All specimens were found between 10:00 – 13:00 hs.

The Bolivian locality of Curqui (Provincia Mendez, Tarija, Fig. 8 View FIGURE 8 ) falls within the proposed limits of the Reserva Biológica de la Cordillera de Sama. This Cordillera reaches more than 4000 m in the Andean Altiplano. The specimens were collected between 3500– 3000 m; at this elevation the slopes are covered by a xeric, scrub forest characterized by large columnar cacti (up to 6 m tall) locally referred to as “cardonales” ( Trichocereus werdemannianus , T. tacaquirensis , and T. tarijensis ). Short shrubs and other cacti interspersed between the “cardonales” of the rocky terrain include Prosopis ferox , Acacia feddeana , Bougainvillea spinosa, Opuntia chichensis, O. spinibarbis, Oreocereus celsianus, Gochnatia cardenasii, Cleistocactus tupizensis, and Tridens avenacea .

Padcaya (2100 m) and Quebrada de Loray (2865 m), southeast of Curqui near the Argentine border in Arce Province, Tarija, are both located in the eastern foothills of the Bolivian Andes. This eastern Cordillera extends southward into the Argentine phytogeographic region known as Prepuna ( Cabrera, 1976), where two of the Argentine specimens (FML 1480 and FML 570) were collected at Acoyte, 7 km W of Santa Victoria, 2500 m ( Santa Victoria Department) and La Caldera, 35 km N of Salta, 1600 m (La Caldera Department), both in the Argentine Province of Salta. The eastern Cordillera in this region is an area of mountains and arid valleys covered by “cardonales” ( Trichocereus pasacana ) commonly associated with “churquis” ( Prosopis ferox ) ( Cabrera, 1976). Finally, the third record for the species in Argentina (FML 1050) lies in the Sierras de Santa Bárbara in Jujuy Province. This sierra is a lower mountain range with elevations averaging 1000–1500 m and the highest peak being 2580 m. These sub-Andean mountains extend in a northeast-southwest direction and form a sharp climatic barrier: the eastern slopes are more humid and covered in forests of the Selva Tucumano-Boliviana; rain shadow effects support Prepuna vegetation on the western slopes ( Cabrera, 1976). Both Rhinocerophis jonathani and R. ammodytoides occur in the Prepuna region of Argentina. The latter species also inhabits arid, rocky and shrub-covered environments ( Cei, 1986, 1993; Cabrera, 2004; Scolaro, 2005; Scrocchi et al., 2006). Although the two species have not been found together, they are likely sympatric or at least parapatric. Rhinocerophis ammodytoides has been observed at Tres Cruces, Jujuy Province, at 3700 m (Moreta, pers. comm.) and this locality is about 87 km from the closest locality for R. jonathani at Acoyte, Salta Province. The similar species R. alternatus extends into northern Argentina but has not been found above 700 m. This species inhabits humid areas (rarely dry ones) that form part of the phytogeographic regions of the Chaco, Espinal , and Pampas ( Cei, 1993; Giraudo & Scrocchi, 2002; Scrocchi et al., 2006).