A NEW SPECIES OF THE GENUS OREOPHRYNELLA ( ANURA ; BUFONIDAE ) FROM THE GUIANA HIGHLANDS

Oreophrynella weiassipuensis sp. nov. is described from Wei-Assipu-tepui on the Guyana-Brazil border. The new species is distinguished from other species of the genus by the presence of well developed post-orbital crests, toe webbing, dorsal skin minutely granular with scattered large tubercles, and reddish brown dorsal and ventral coloration.


INTRODUCTION
The bufonids of the genus Oreophrynella are a group of noteworthy small toads, endemic to the highlands of the Guiana Region in northeastern South America.Members of this genus are frogs of small size (< 26 mm SVL), characterized by opposable digits of the foot, tuberculate dorsal skin, and direct development (McDiarmid, 1971;McDiarmid and Gorzula, 1989;Señaris et al., 1994).
The genus was created by Boulenger (1895a, b) for the newly described species O. quelchii from the summit of Mount Roraima.Boulenger (1900) described a second species of the genus, O. macconnelli, from the forest at the base of Mount Roraima at 1067 m.Almost 90 years later a third species, O. huberi, was described from the summit of Cerro El Sol (Diego-Aransay and Gorzula, 1987), a tepui which is not part of the Roraima formation.Señaris et al. (1994) reviewed the Guiana highland bufonids and described two additional species, O. nigra from Kukenán and Yuruaní tepuis, and O. vasquezi from Ilútepui.Finally Señaris (1995) described O. cryptica from Auyán-tepui.
On July 2000 a speleological expedition to Wei-Assipu-tepui, conducted by members of the Italian and Venezuelan speleological societies (Carreño et al., 2002;Villarreal et al., 2002), collected a small but interesting collection of amphibians, including two specimens of the genus Oreophrynella, one of them corresponding to O. quelchii and the other one to a new remarkable species described below.

MATERIALS AND METHODS
Measurements were made to the nearest 0.1 mm using a Mitutoyo digital caliper.The numbered diagnosis follows the format of Señaris et al. (1994) and Señaris (1995).Two different types of cephalic crests are recognized in Oreophrynella: frontoparietal crests, located on the outer border of the frontoparietal, and postorbital crests, extending from the posterior margin of the eye, around the tympanic region to below the eye.
In Oreophrynella the digits of the hand and foot are joined at their bases by a fleshy extension of thick skin continuous with the sole.This thickened integumental connection between the digits differs from the webbing which connects the fingers or toes in other frogs (e.g.hylids, centrolenids, ranids).Nevertheless, we use the term "webbing" to refer this particular structure in Oreophrynella.
The holotype of the new species was compared with the type series of O. cryptica, O. huberi, O. nigra, O. vasquezi, material from the type locality of O. quelchii (Appendix), and published descriptions of O. macconnelli.
Etymology.The specific epithet weiassipuensis refers to the name of the locality where the species was collected.
Diagnosis.A species of the genus Oreophrynella that can be distinguished of the other species by following combination of characters: 1) frontoparietal crests absent; post orbital crests well developed; 2) dorsal skin minutely granular with scattered large tubercles, especially on the upper eyelids and flanks; 3) ventral skin granular, with few small tubercles; 4) webbing of hand and foot well developed; 5) in life dorsum reddish brown with scattered darker brown marks and a fine dark mid-dorsal line; flanks dark brown; dorsum of hands light brown with minute reddish brown spots; 6) throat and chest reddish brown; belly slightly darker than the remaining ventral surface; fingers and toes light brown ventrally.4A).Hindlimbs long, slender; foot with short, somewhat flattened toes; the first three toes united at the base, opposed to the other two; relative lengths of toes 2=3<5<1<4; sole completely tuberculate, with a large, elongate inner metatarsal tubercle, and smaller, round subarticular tubercles (Fig. 4B).When the hindlimb is extended forward along the body, the knee reaches the shoulder.Dorsal skin minutely granular with scattered large, rounded or oval tubercles; upper eyelids with large, rounded, elevated tubercles, with those close to the external margin aligned in a distinct row (Fig. 1); limbs with a greater density of large rounded tubercles.Ventral skin granular with scattered small flattened tubercles.Cloacal opening directed posteriorly at level of the thighs.
Color in preservative.Dorsum reddish brown with a thin dark brown mid dorsal line and small spots, slightly darker in the occipital region, eyelids, and flanks; nostril area lighter than background coloration.Loreal region and postorbital area reddish brown with irregular darker brown bars surrounding the postorbital crests.Limbs light reddish brown with darker tubercles; hands and feet light brown dorsally with numerous minute brown spots that delimited the margins of the fingers and toes.Throat, chest, and ventral surfaces of limbs light reddish brown; flanks and cloacal area dark brown with some lighter tubercles; palms and soles light brown with a gray wash.
Color in life.The same pattern described above, but more intense and contrasting.
Distribution and ecology.Oreophrynella weiassipuensis is known only from the type locality on Wei-Assipu-tepui on the frontier between Brazil and Guyana.It was collected on moss in a wet forest at the bottom of a large chasm.Other anurans found on the summit of the Wei-Assipu-tepui include Colostethus sp., Oreophrynella quelchii, three undescribed species of Stefania (goini group) and Tepuihyla sp.(Villarreal et al., 2002).
Comparisons with other species.Oreophrynella weiassipuensis can be distinguished from all other species of the genus by the well developed webbing and the reddish brown dorsal and ventral coloration.

DISCUSSION
The bufonid genus Oreophrynella is one of the most characteristic components of the anurofauna of the Guiana Region.McDiarmid (1971) considered Oreophrynella a very specialized frog, restricted to the Guiana Shield.The genus currently consists of seven species, five inhabiting the summits and slopes of the Roraima chain (O. macconnelli, O. nigra, O. quelchii, O. vasquezi, and O. weiassipuensis) and the remaining two species (O.cryptica and O. huberi) known from the summits of Auyán-tepui and Cerro El Sol, respectively.Another undescribed species is known from the northeastern slope of Mount Ayanganna in Guyana (Lathrop and MacCulloch, pers.comm.).Rivero (1970) and Hoogmoed (1979) postulated that Oreophrynella derived from a paleo-fauna that evolved in an ancient sandstone plain during the Mesozoic or Tertiary, followed by intensive erosional dissection (Plateau Theory).Besides its origin, Señaris et al. (1994) discussed the great morphological similarity between neighboring species of the Roraima chain summits and considered the lowering of South American tropical temperature during the glacial periods in the Pleistocene (Van der Hammen, 1974) as a possible cause of the descent of the lower limit of the highland tepui ecosystems to at least 500 m below its present location, allowing contact between different Oreophrynella populations for hybridization and/or genetic flux, followed by a period of speciation.This theory would explain the resemblance among O. quelchii, O. nigra, and O. vasquezi, which occur on adjacent peaks of the Roraima chain (Señaris et al., 1994), or O. cryptica and O. huberi from Auyán-tepui and Cerro El Sol, respectively (Señaris, 1995).However, this proposal does not seems totally explain the distributions of O. macconneli and O. weiassipuensis, the latter very similar to O. cryptica and O. huberi.Oreophrynella cryptica, O. huberi, and O. weiassipuensis share well developed cranial crests (restricted to the post orbital area in O. weiassipuensis) (Figs.5D-F) and less tuberculate dorsal skin than other species.Oreophrynella weiassipuensis and O. huberi share a reddish dorsal coloration, in contrast with the dark brown or black color of the other species.The great similarity between O. cr yptica, O. huberi, and O. weiassipuensis suggests a possible relationship between them.However, we are uncertain about the presumed derived condition of these two characters and any conclusion about the relationships of Oreophrynella species is merely speculative at this point.
Most species of Oreophrynella are endemic to a single mountain, except O. nigra which occurs on both Kukenán-tepui and Yuruaní-tepui (Gorzula and Señaris, 1999;Mägdefrau and Mägdefrau, 2000;McDiarmid and Gorzula, 1989;Señaris et al. 1994) and O. quelchii from Roraima and Wei-Assipu-tepui (Villarreal et al., 2002).Roraima and Wei-Assipu-tepui are very close (2.5 km between summits) and linked by a ridge of medium altitude.Kukenán and Yuruaní are also in close proximity to each other (3.5-4 km).Myers and Donnelly (2001) suggested a past faunal interchange by a system of ridges connecting the ba-  ses of some northwestern tepuis, to explain the presence of some shared species.This hypothesis could also be applied to the eastern region, where adjacent mountains connected by upland ridges (1600-2100 m) share the same Oreophrynella species, e.g.Kukenán and Yuruaní (O.cryptica), and Roraima and Wei-Assipu-tepui (O.quelchii).Nevertheless, this hypothesis fails to explain what conditions favored this interchange only in the past.
The presence of Oreophrynella quelchii and O. weiassipuensis on Wei-Assipu-tepui represents the first known case of two species of the genus sympatric (Villarreal et al., 2002), although occupying different habitats.Oreophrynella quelchii was observed in a bare rocky area, while O. weaissipuensis was found in a forested area at the bottom of a large pit (Villarreal et al., 2002); it is possible that O. weiassipuensis is restricted to this habitat.
Furthermore, O. weiassipuensis differs from O. macconnelli, O. nigra, O. quelchii, and O. vasquezi by the presence of postorbital crests and dorsal skin with a low or medium density of tubercles.Oreophrynella.weiassipuensis differs from O. cryptica and O. huberi by the absence of frontoparietal crests (Figs.5A-C) and the reddish brown dorsal and ventral coloration .