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A small ranid frog with a moderately warty skin. Adult males measure 11-19 mm and weigh 0.1-0.63 g. Adult females measure 16-23 mm and weigh 0.55-1.15 g. The average index head width / SVL is 0.31 (s.d. + 0.04; 0.25-0.38; N = 16). With eyelid cornicle. The tympanum is very small and barely discernible. Males have single subgular vocal sacs. A distinct supratympanal fold, a small inner metatarsal tubercle and a tarsal tubercle are always present. Only residuary webbing on the feet. Tips of fingers and toes not enlarged.
The animals described by Perret (1988a) apparently have somewhat more extended webbing than the Comoé frogs. He gives up to 20 mm for males and up to 25 mm for females (SVL).
Voucher specimens:SMNS 8961 1-16 + tadpoles.
Coloration: The frogs are usually uniform olive to light brown. The warts may have darker borders. Some animals have a vertebral band starting behind the eyes which is almost invariably red with yellow or orange borders. Rarer are frogs with a red transverse band on the back. On some specimens, two bands form a cross on the back. The thighs either lack any pattern, or they bear 1-2 dark transverse bands. The posterior parts of the thighs never bear a light longitudinal line. On the flanks a feebly marked black lateral stripe may be present. Many animals have dark bars on the edges of their lower jaws. The vocal sac of the male is dark violet to black. The throats of the female bear some marginal dark spots. The breast, flanks and ventral edges of the thighs and shanks are similarly spotted black. Two dark patches are frequently present in the pectoral region. The rest of the venter is white. Guibé & Lamotte (1963) quote four dark bars on the thighs and a light vertebral band with dark borders. In alcohol, the warts often turn smoother, and the surrounding areas frequently appear darker. The vertebral bands fade. The throat in males almost loses its pigmentation.
Voice: Recorded whistling calls last 0.26 sec at a frequency of 3.1-5.4 kHz. This call is very similar to those of Arthroleptis species. In addition, males sometimes utter long buzzing tones which could not be recorded. It recalls the song of ensiferan grasshoppers. I cannot decide which of these sounds is the advertisement call. However, both calls are uttered by solitary males. According to Schiøtz (1964c), the buzzing sound, that he also illustrates, is an advertisement call. It lasts 2 sec and consists of approx. 200 pulses, reaching its maximum frequency intensity at 5.5 kHz.
Spawn: Clutches have not yet been found at Comoé National Park. In captivity three females from Tai National Park produced six clutches within two month. Despite the fact that only one male was present spawning of two to three females was synchronized. Only one clutch was fertilized at a spawning event. Time between two events was 4-5 weeks. The surface layers consisted of 75-220 eggs (152 + 60). The eggs had a diameter of less than 1 mm and dark gray and white poles. The tadpoles hatched within three days. At Lamto, females are reported to produce two clutches per year with 290 + 144 eggs, each. The egg diameter was 0.8 mm (N = 69; Barbault & Pilorge 1980, Barbault 1984).
Tadpoles: Freshly hatched tadpoles are minute (approx. 2-3 mm) and have external gills. Gills were reduced within another two days. The tadpoles resemble very much those of other Phrynobatrachus species. The keratodont formula is 1 / 1+1 // 2+2 / 1. The filamentous papillae of P. latifrons and P. francisci are always (?) absent. Tadpoles with developed hind legs measured 6.1-6.4 mm (BL; TL: 13.5-16.5mm). The smallest frog ever collected measured 8 mm and weighed 0.05 g.
Schiøtz (1963) describes larvae whose dorsal tail fin is somewhat narrower and begins at a more craniad position, compared to those that I have collected. Both the fin and the base of the tail axis bear numerous black spots. He gives the keratodont formula 1 // 3, but writes that this is perhaps not the normal one, because of the abnormal development of the said larvae. The largest tadpole he ever found measured 15 mm (TL). The SVL of freshly metamorphosed young was 6 mm. Loveridge (1941) gives 12 mm for young frogs.
P. calcaratus differs from other savanna species of the genus Phrynobatrachus species by the small eyelid cornicle, the body shape and the absence of webbing. Five other species with an eyelid cornicle occur in West Africa, but they may easily be differentiated by their different ventral pattern (Perret 1988a). Nieden (1908) considered P. cornutus (Boulenger, 1906) a synonym of P. calcaratus. According to Perret (1988a) P. cornutus occurs in Cameroon, Fernando Póo and (possibly) Gabon. Males measure 14-16 mm (SVL) and ventrally have two large black patches in the pectoral region. The upper part of the breast also bears black blotches. The venter of females (SVL: 18-20 mm) is roughly spotted black. Their body shape of P. calcaratus resembles that of female Arthroleptis without distinct color pattern. However, Arthroleptis always lacks an eyelid cornicle. The males of Arthroleptis are (mostly) characterized by their extremely long third fingers. For a human, the whistling calls of
P. calcaratus and Arthroleptis poecilonotus resemble each other. When we tried to catch calling Arthroleptis males we found our first P. calcaratus instead.
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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