Karoo Dainty Frog (Frogs of South Africa)

Karoo Dainty Frog

Cacosternum karooicum

Summary ¹

The Karoo dainty frog (Cacosternum karooicum) is a species of frog in the Petropedetidae family. It is endemic to South Africa. Its natural habitats are subtropical or tropical dry shrubland, intermittent rivers, intermittent freshwater marshes, rocky areas, and ponds.

Description ²

Diagnosis: This species can be diagnosed as a member of the genus Cacosternum by the following characteristics: clavicle absent, omosternum severely reduced, small size, irregularly spotted abdomen, tympanum not visible, no toe webbing, no midtarsal tubercle, no medial lingual process. It can be distinguished from the similar species C. namaquense by a lack of longitudinal dorsal glands in C. karooicum (vs. paired, rust-colored glands in C. namaquense), having a thick musculus cutaneous pectoris (vs. absent in C. namaquense), medioventral ends of coracoids only occasionally faintly nicked (vs. pronounced bifurcation in C. namaquense), wider frontoparietal bones compared to C. namaquense, adpressed Toe V reaching to or beyond second subarticular tubercle of Toe IV (vs. Toe V falling short in C. namaquense), fringing on digits absent or rudimentary (vs. well-developed in C. namaquense, except for the population from far northern Namibia), presence of small outer metatarsal tubercle (vs. usually absent in C. namaquense, dorsum covered with small, round, evenly spaced warts (vs. smooth dorsum, rarely having warts, in C. namaquense), dorsal coloration uniform olive-brown to khaki-brown, sometimes with orange or red tint (vs. dark blotches or rosettes on a mottled lighter background in C. namaquense), no interorbital bar (vs. pale triangular patch with the base making an interorbital bar in C. namaquense), no inverted V-shaped patch on mid-dorsum (vs. inverted V-shaped patch present in C. namaquense) (Boycott et al. 2002).

Description: Cacosternum karooicum measures from 23.3 to 30.8 mm SVL. The body shape is flattened and thin in appearance. The snout is rounded. The tympanum is not visible. The supratympanic fold is present but not well-developed, with the back portion becoming part of a glandular fold of excess skin. A poorly defined glandular ridge is in line with the edge of the upper jaw and stretches almost to the base of the forelimb. The skin is evenly covered with small round glandular warts. Limbs are moderate in length. Finger tips are slightly rounded with the third finger longest in length, followed by the fourth, second, and first. Supernumerary tubercles of hands were well-defined while the palmar tubercle was divided, with both sections equivalent in size. Toes possess slight lateral fringes, along with a trace of webbing along the base of the toes between the second and third, third and fourth, and fourth and fifth toes. The fourth toe is the longest, followed by the third, fifth, second, and first. The outer metatarsal tubercle is present. The inner metatarsal tubercle is medium-sized, conical, and outward-projecting. Subdigital tubercles of the feet are conical, small, and prominent; in comparison, subdigital tubercles of the hands are larger and more rounded. Males have nuptial pads on the upper surfaces of the first and second finger, and a vocal sac (Boycott et al. 2002).

This species is olive-brown dorsally, sometimes with a shade of reddish-brown or bronze. The venter is white with large, irregularly shaped yellow-brown patches. Ventral surfaces of the limbs are dirty mustard yellow-brown ventrally, with the yellow bordered by gray and white markings (Boycott et al. 2002).

Tadpoles measure 41 mm at Gosner stage 34. The tails are long. Nostrils are oval and rimmed. The spiracle is sinistral and situated along the body. The vent is basicaudal and dextral. The large mouth is ventral, and not visible dorsally. A marginal row of oral papillae with a wide rostral gap is present. Intramarginal papillae can be found at the posterior of the mouth and laterally to labial tooth rows only; there are estimated to be about 5 per row. There are only 2 single papillae anteriorly per side (Boycott et al. 2002).

The species epithet karooicum refers to the type locality, a semidesert region in South Africa. "Karoo" is derived from the Khoi-Khoi word "Karo", meaning thirsty (Boycott et al. 2002).