Description
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.

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Angola, Benin, Botswana, Cameroon, Central African Republic, Chad, Congo, Congo, the Democratic Republic of the, Eritrea, Gambia, Ghana, Guinea, Guinea-Bissau, Kenya, Liberia, Malawi, Mali, Mozambique, Namibia, Nigeria, Senegal, Sierra Leone, Somalia, South Africa, South Sudan, Tanzania, United Republic of, Togo, Uganda, Zambia, Zimbabwe

	View distribution map in BerkeleyMapper.
	View Bd and Bsal data (15 records).

Range: This widespread species inhabits all the savanna regions of Africa south of the Sahara. According to Frost (1985), it is encountered from Senegal to southern Africa. In particular, records exist for the following countries: Senegal, Gambia, Guinea Bissau, Sierra Leone, Liberia, Guinea, Mali, Ivory Coast, Ghana, Togo, Benin, Nigeria, Cameroon, R.D. Congo, Congo, Central African Republic, Chad, Somalia, Ethiopia, Eritrea, Uganda, Kenya, Tanzania, Zanzibar, Malawi, Zambia, Zimbabwe, Mozambique, South Africa, Namibia, Botswana, Angola (Peters 1854, 1878, 1882c, Günther 1864b, Pfeffer 1893, Boulenger 1906, 1910, 1919, Nieden ?1908, ?1910a, b, 1915, Lönnberg 1910, Chabanaud ?1919b, Noble 1924, Loveridge 1925, 1929, 1930, 1933, 1936, 1941, 1942, 1955c, 1957, Scortecci 1929, 1940, Parker 1930, 1932, 1936?a, b, c, Witte 1934, 1941, Sanderson 1936, Mertens 1938a, 1955b, Orton & Morrison 1946, Laurent 1952e, 1964b, 1979a, Lamotte & Zuber-Vogeli 1953, Romer 1953, Guibé & Lamotte 1957, 1958a, b, 1960, Taylor & Weyer 1958, Schmidt & Inger 1959, Schiøtz 1963, 1964a, b c, 1967, 1968, Poynton 1964a, c, 1966, 1970, 1991, Perret 1966, Barbault 1967, 1974, 1984, Lamotte 1967b, 1969, Stewart 1967, Walker 1968, Amiet & Perret 1969, Euzet et al. 1969, Maeder 1969, Wake & Kluge 1969, Broadley 1971, 1991, Amiet 1973a, 1974b, 1975, Stevens 1974, Barbault & Trefaut-Rodriguez 1978, Miles et al. 1978, Joger 1981, 1990, Poynton & Broadley 1985b, Wager 1986, Lambert 1987, Zug 1987, Branch 1988, Hughes 1988, Lambiris 1988, 1989, Branch 1990, Gruschwitz et al. 1991a, Channing & Griffin 1993, Simbotwe & Mubemba 1993, DuPreez 1995, Passmore & Carruthers 1995, Rödel 1996, 1998b, Joger & Lambert 1997).

Habitats: During the dry season, single animals are found under stones on river banks, whereas in the rainy period the borders of savanna ponds are colonized. This frog is generally characterized as preferring open landscapes (e.g. Schiøtz 1967, Poynton 1970). Hughes (1988) reports that P. oxyrhynchus lives within any type of habitat with the exception of true rainforest. Humid savanna regions form its typical habitat (e.g. Lamotte 1967b, Walker 1968, Broadley 1971, Poynton & Broadley 1985b, Joger 1981, Gruschwitz et al. 1991a, Simbotwe & Mubemba 1993). Some authors also quote more arid and open forest habitats (e.g. Schiøtz 1963, 1964c, 1967, Amiet 1974b, Poynton & Broadley 1985b). Guibé & Lamotte (1958a), Perret (1966) and Amiet (1975) observed this species both in forests and adjacent savannas. As far as older studies are concerned, observations from rainforest areas are possibly based on false identifications, i.e. the frogs might have been confused with P. aequiplicata (e.g. Sanderson 1936). Loveridge (1942, 1957) believed that a lowland subspecies inhabiting savannas (P. o. oxyrhynchus) and a montane form preferring forest habitats (P. o. gribinguiensis) can be distinguished in East Africa. He placed all western records within either R. o. gribinguiensis or R. o. superciliaris.

Life History, Abundance, Activity, and Special Behaviors
Spawn: Single floating egg layers. Eggs with brown and white poles. In Lamto, females produced 3476 ± 1542 eggs, with a diameter of 1.3 mm (Barbault & Trefaut Rodriguez 1978, Barbault 1984). Clutch sizes was positively correlated with female’s SVL. An egg diameter of 1.3 mm was also reported by Wager (1986) and Lambiris (1989). According to Lambiris (1989), eggs were deposited singly on the water surface. Wager (1986) however reports that the eggs are either deposited as a single egg layer floating on the water surface or attached in portions of up to 500 eggs (clutch diameter: 7.5–10 cm) right below the water surface.

Biology: When the rains set in, the frogs move from the rivers into the open savanna where they are among the first anurans to deposit their clutches. I found P. oxyrhynchus particularly often at small ponds lacking any vegetation. This was the first species that accepted the concrete pools we built for some experiments, too. At these sites, single males called at night from banks. We almost invariably found them sitting on the bare ground without any cover. Exposed calling sites in close vicinity to open water are also described by Lambiris (1988). Small waters serving as spawning sites are mentioned by Poynton & Broadley (1985b) for South Africa, and by Amiet (1974b) for Cameroon. Both the Cameroon frogs (Amiet 1974b) and those at Comoé National Park spawned at the first rainfall. If precipitation happens to be sufficient, breeding takes place throughout the rainy season. At Lamto, the frogs only spawned between February and May (local rainy season: March-November, Barbault & Trefaut Rodriguez 1978). Passmore & Carruthers (1995) report that calling activity in South African frogs lasts from 11.00 h p.m. to 04.00 h a.m.

At Lamto, this species is adult at the age of 8–9 months, usually living just another 12 months. The mortality of younger frogs is considerably higher than that of adults (Barbault & Trefaut Rodriguez 1978, Barbault 1984). The said authors report that only one clutch per female and year is produced. Thanks to their enormous muscular power and their very timid habits, these frogs are very difficult to catch. Leaps of 3 m and more reaching heights of 1 m are likely to be just the lower limit: Wager (1986) reports on leaps covering 10 m, i.e. a distance corresponding to 200 times of the frogs body length! At Lamto the diet mainly consists of spiders and orthopterans (Barbault 1974d). Loveridge (1937) and Simbotwe & Mubemba (1993) equally cite arthropods, or more generally small invertebrates, as prey. In the grasslands of Natal Pickersgill (pers. comm.) observed this species in early morning when grass is wet with dew up to a mile away from standing water.

Larva
Tadpoles: The compact tadpoles have comparatively short tails. The dorsal part of the fin inserts at the mid-body level, being much broader and more curved than the ventral part. The beige tadpoles have oral discs surrounded by a single lateral and 2–3 caudal rows of papillae. Additional papillae are often present in the corners of the mouth. The horny beaks are moderately massive and serrated. Keratodont formula: 1 / 1+1 // 2.

Wager (1986), Lambiris (1988) and Guibé & Lamotte (1958a) give an identical formula. Guibé & Lamotte (1958a) also mention animals with the formula 1 / 2+2 // 2. Their lateral and caudal papillae are said to be arranged in 1–2 rows. The longest tadpole is reported to measure 37 mm, whereas the SVL of freshly metamorphosed frogs measured 15 mm. Lambiris (1988, 1989) gives a TL of 40 mm (BL: 14 mm) and the keratodont formula 2 // 2. The largest tadpole collected by Wager (1986) was 54 mm long (TL). At Lamto, the frogs metamorphose within 3–4 weeks (Lamotte 1983), those in Zimbabwe within 2 months (Lambiris 1989). Orton & Morrison (1946) give 15.5mm for metamorphosed frogs, and 19–26 mm are quoted by Loveridge (1942).

As the data published by Guibé & Lamotte (1958a) are based upon Lamotte & Zuber-Vogeli (1953), they should be evaluated with caution. The latter report on choruses comprising more than 100 males, a statement which does not correspond at all with my observations (see below). Some days later, the collected tadpoles perished, and the authors collected new larvae at the same pond. The appearance of these tadpoles was reported to be similar, whereas their size was either identical or smaller than that of their predecessors. However, I have never observed the growth of captive tadpoles to proceed as rapidly as in the wild even when climatic conditions were identical. As the larvae described by Lamotte & Zuber-Vogeli (1953) hatched within two days, their general development was supposedly identical. In the savanna, I have never observed Ptychadena-tadpoles that needed more than one day for hatching. However, animals from Zimbabwe seem to hatch within two days, although Lambiris (1989) does not indicate whether this happened in captivity or in the wild. The variable form of the oral discs described by Lamotte & Zuber-Vogeli (1953) (e.g. additionally the keratodont formula 1 / 1+1 // 3) possibly supplies evidence for the fact that these tadpoles actually belong to different Ptychadena-species. Tadpoles collected at a given pond and described, assuming that they belong to the same species as the adults observed at that water, might frequently have given rise to virtually useless descriptions. Specifications concerning tadpole morphology are only acceptable if the respective clutches can be assigned to identifiable parents, or if the larvae have been reared up to an age permitting their identification. Most often this is not possible even in already metamorphosed froglets of species of certain genera. Scortecci (1940) gives an additional keratodont formula for animals from Eritrea (1 / 2+2 // 1+1 / 2).

Comments
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.
For references in the text, see here

References

Phaka, F.M., Netherlands, E.C., Kruger, D.J.D., Du Preez, L.H. (2019). Folk taxonomy and indigenous names for frogs in Zululand, South Africa. J Ethnobiology Ethnomedicine 15, 17. [link]

Rödel, M. O. (2000). Herpetofauna of West Africa, Vol. I. Amphibians of the West African Savanna. Edition Chimaira, Frankfurt, Germany.

Species Account Citation: AmphibiaWeb 2023 Ptychadena oxyrhynchus: Sharp-nosed ridged frog <https://amphibiaweb.org/species/4947> University of California, Berkeley, CA, USA. Accessed Nov 26, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 26 Nov 2024.

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