(Linnaeus, 1758)
Geometric tortoise
Recognition
The carapace (to 16.5 cm; Ernst Baard, pers. comm.) is elliptical (widest posteriorly), domed with abruptly descending sides, deeply notched at the small cervical, and rarely serrated posteriorly. Vertebrals are broader than long. Each carapacial scute is covered with raised growth annuli, and these often cause the center (areolus) of the vertebrals tobe raised in a conical or pyramidal fashion. There are 11 or 12 marginals on each side, and the supracaudal is not divided. The carapace is dark brown or black, and each vertebral and pleural scute has a yellow center with yellow stripes radiating outward from it (8-15 rays on each vertebral, 9-12 on each pleural). The plastron is large and well-developed. Its forelobe tapers to the front, is narrower than the hindlobe, and bears a shallow anterior notch as the gulars are slightly divergent. The hindlobe tapers toward the rear and has a deep posterior notch. Single axillary and inguinal scutes are found on the bridge. The variable plastral formula is: abd > gul >< hum >< fem >< an < pect. The plastron is yellow with some brown or black pigment along the seams. The head is moderate in size with a convex forehead, a nonprojecting snout, and a hooked upper jaw. Its prefrontals are longitudinally divided and followed by subdivided frontal scales. Other head scales are small. Head and neck are dark brown or black with irregularly shaped yellow reticulations. The black or dark-brown forelimbs are covered anteriorly with six or seven longitudinal rows of large, nonoverlapping, irregularly shaped yellow scales separated by smaller scales. Hindlimbs are also dark colored, and lack large conical tubercles on their thighs.
Males have concave plastra and longer, thicker tails. Females are larger and heavier.
Distribution
Psammobates geometricus is restricted to southwestern parts of Western Cape Province, South Africa (Loveridge and Williams, 1957; Baard, 1993). Apparently it was once more widespread, but loss of habitat to farming, unplanned and uncontrolled wildfires, and invasion of alien vegetation (Baard, 1993) has caused a decline until it is now one of the most endangered tortoises in the world. Nature reserves have been established to protect the tortoise.
Habitat
The geometric tortoise lives in low-lying open patches of uncultivated land with acidic sandy soil and vegetation of medium height (50-100 cm); with 2-5% annual herbaceous cover, 25-50% shrub cover, 10-25% geophytes, perennial grass cover of 5-10%, Aspalathus sp. present at 5-10% canopy cover, and 350-600 mm of winter rainfall (Baard, 1995).
Natural History
Eglis (1962) reported olfactory movements, which may be associated with courtship, consisting of stiffly executed, single, left-to-right sideways motions of the head.
Mating occurs in the spring (September-November; Baard, 1989). One clutch of 2-8 eggs is laid each year (Baard, 1989, 1994). The eggs are ovoid, 30-32 x 23-24 mm in diameter, and have brittle shells; they hatch in March-May (Rau, 1976; Branch, 1988), after an incubation period of 5-8 months (Baard, 1994).
Hatchlings are 30-40 mm in carapace length, and many show a pattern consisting of a single yellow X-shaped mark on each vertebral and pleural. Their plastra have a broad yellow-bordered central black blotch with a yellow midseam and various yellow reticulations.
Psammobates geometricus feeds on a variety of grasses, reeds, sedges, herbs, and shrubs (Rau, 1969; Baard, 1994).
Remark
Wallin (1977) showed that the Linnaean type of P. geometricus was actually a specimen of Geochelone elegans. Since the type species of Geochelone is G. elegans and the type of Psammobates is geometricus, following the rules of priority would require that all of Geochelone be changed to Psammobates, whose type species would be geometricus. In order to prevent this chaos, Hoogmoed and Crumly (1984) have designated an appropriate lectotype, thereby avoiding an ICZN decision.
IUCN Red List Status (1996)
Endangered (A1ac, B1+2c). Less than 3% of its habitat remains. P. geometricus is protected in five nature reserves, the rest is under private ownership (Ernst Baard, pers. comm.). |
