Comprehensive DescriptionRead full entry
A big ranid with a pointed snout and very long legs. Adult males measure 40–53 mm (SVL), females 51–64 mm. Several short dorsal longitudinal ridges. Like the other ridges, the two median ones emerge on a level with the posterior border of the eyes. They are rarely continuous, but end in the middle of the back. Two other ridges, closer to the vertebra and slightly overlapping longitudinally with the median ridges, extend from the eyes to the vent. On each side, up to three further, short ridges appear laterally on the back. A feebly defined lateral ridge may be present. Apart from the ridges the skin is smooth. The tympanum is clearly visible, and it reaches almost the eye diameter (0.8–1.0). It is bordered dorsally and ventrally by short ridges. Males have paired lateral vocal sacs, enlarged thenar tubercles and swollen first fingers. The bases of the second and third fingers may be dorsally swollen, too. The hind legs are exceedingly long and muscular. They also bear longitudinal ridges. When the leg is extended forward along the flank, the middle of the shank is located beyond the snout tip. The thighs reach 0.6–0.7 of the SVL, the shanks reach 0.7–0.8 and the feet incl. longest toe measure 0.8–0.9 of the SVL. Toe-tips and finger-tips are not enlarged. The slender inner metatarsal tubercle reaches 0.1–0.4 (rarely 0.5) of the shortest toe length. Webbing formula: 1 (0), 2 i/e (0.5–0) or (1–0), 3 i (0.5) or (1), 4 i (0.5) or (1), 5 (0). A specimen from Natal (SMNS 2093) has the following formula: 1 (0.5), 2 i/e (1–0.5), 3 i (1), 4 i/e (2–0.5), 5 (0). Guibé & Lamotte (1960) give 60 mm (SVL) for males and up to 64 mm for females. Perret (1966) quotes 68 mm for females. Loveridge (1937) gives up to 42 mm for males, and up to 55 mm for females, but cites as well P. o. gribinguiensis females with 67 mm.
Voucher specimens:SMNS 8954 1–2 + tadpoles; SMF one male without number.
Coloration: The rather uniform basic color of these frogs is dark beige to olive. Dark spots are particularly numerous in the areas surrounding the dorsal ridges. However, smaller spots equally occur on the flanks. If a lateral ridge is well-defined, it is usually lighter colored than the other ridges. The extremities, in particular the anterior parts of the hind legs, bear broad dark transversal bands, four to six of which may appear on the shanks. The posterior part of the thighs are mottled in black and yellow; the yellow patches occasionally fuse into longitudinal bands. The forelegs are flesh-colored ventrally. A black line emerges at the snout tip, forming a black temporal triangle surrounding the posterior part of the eye and ending with the posterior border of the tympanum. The latter is surrounded by an additional pale ring. The upper part of the iris is silver. The medio-dorsal part of the eye is black, the caudal one often orange or reddish. The venter is gray or white. The border of the lower jaw occasionally shows some black markings. The webs are black. Very rarely, the head, particularly its lateral parts, the dorsal and lateral ridges, the ridges on the extremities and the ridge running from the eye to the region beneath the tympanum are red. The basic color of the respective animals is a very dark brown; however, the dark markings are clearly distinct. The patches on the thighs do not form continuous bars, but are divided longitudinally. Coloration in alcohol is almost similar to live coloration, at most somewhat vague or faded. The colors are more grayish. The posterior part of the eye border often turns reddish.
Voice: The low, creaking call lasts 0.83-0.96 sec and comprises two similar pulses that last 0.01–0.02 sec and that are separated by longer pauses of 0.03 sec. It consists of two independent harmonies with frequencies from 1.39–2.29 and 2.5–3.8 kHz. The pauses between the calls last 0.58 sec. I always had the impression of a very soft call. In South African frogs the advertisement call is very loud (Pickersgill, Vences, pers. comm.). It is a low, harsh, pulsatile screech, which resembles rapidly dragging a stick across iron railings (Pickersgill, pers. comm.). At those places where I have heard the respective call, I exclusively saw P. oxyrhynchus males. However, as I always failed to observe the males while calling it might be that the analyzed calls are in fact those of P. tournieri (compare the respective account). Sonagrams of this species have also been published by Schiøtz (1964c), Amiet (1974b), Passmore (1977) and Passmore & Carruthers (1995). Both the calls in Passmore (1977) and those in Passmore & Carruthers (1995) and Amiet (1995) basically show the same structure as the call recorded at Comoé National Park, but comprise less pulses per call, and their frequency is somewhat lower. Amiet (1974b) pertinently describes the call as a low "cra-cra-cra". The frogs whose calls were recorded by Schiøtz (1964c) were calling from an iron tank, a fact which might explain the different sonagrams. Further, Passmore (1977) describes an "initial" call preceding the advertisement call, and an aggressive call.
This account was taken from Rödel, M.-O. (2000), Herpetofauna of West Africa vol. I. Amphibians of the West African Savanna, with kind permission from Edition Chimaira publishers, Frankfurt am Main.
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