Endemic to coastal South Africa and Namibia, the angulate or bowsprit tortoise, Chersina angulata, is a monotypic genus with "two distinct evolutionary lineages associated with the southern and western regions of South Africa" (Hofmeyr, 2009). The biological term ‘monotypic’ indicates one type or representative and typically refers to a genus that has a single species. The distinct lineages and geographic variations of the angulate tortoise will be discussed in greater detail in the "Description" section of this article.
Scientifically described by the German naturalist August Friedrich Schweigger (1783-1821) in 1812, the angulate tortoise is also known commonly as the angulated tortoise, the bowsprit tortoise, the South African bowsprit tortoise, and is known locally as rooipens (Afrikaans vernacular for red-bellied tortoise) [Hofmeyr 2009].
The definition of the term bowsprit is as follows: a spar that extends forward from the prow (also called the bow) of a sailboat or a ship. In one of the common names of C. angulata, the word bowsprit refers to the stout, single gular scute protruding under the species' chin.
The genus name Chersina derives from a Greek word root chers- meaning "dry land" and refers to a land tortoise, while the species name angulata derives from a Latin word root angul- that means "angled."
One of the most abundant species of tortoise in South Africa, the angulate tortoise inhabits a variety of ecoregions and climates ranging from semidesert biomes along the West Coast to Mediterranean climates in the southeast and temperate climates in the southwest (Hofmeyr, 2004).
A small to medium-sized member of the tortoise family the Testudinidae, the angulate tortoise inhabits ecoregions generally described as coastal scrub within its southern Africa range. Reaching a carapace length of 12 inches (30 centimeters) at maturity, C. angulata features a domed upper shell that is hingeless, elongated, and varies considerably in coloration (Chersina angulata). Typically yellowish-brown to olive, the carapacial scutes have dark brown to black borders and a brown to black patch in the center of each vertebral and pleural scute. Marginal scutes have narrow, dark triangular markings near the front edge of each scute (Chersina angulata). The carapace frequently fades in coloration and patterning as the tortoise ages, with older tortoises often appearing uniformly yellowish-tan.
Yellow to reddish in background coloration, the angulate tortoise's plastron features a wide, dark, irregular stripe centered on its length. The species' "large, protruding undivided gular scute" is distinctive (Hofmeyr, 2009), and distinguishes it from all other species of South African tortoises.
Typically brown or black in color, the head of C. angulata may be yellow on the top with a moderately hooked jaw. Its forelimbs are olive to yellow; hindlimbs are dark on the outer surface and yellow on the inner (Chersina angulata).
Displaying pronounced sexual dimorphism, angulate tortoise males are typically larger than females with longer, thicker tails, deeply concave plastra, and larger gular projections (Chersina angulata). The carapace of the male angulate tortoise tends to be less domed than that of the female.
The species also inhabits islands off the coast of South Africa, including Dassen and Robben Islands off the southwest coast, where the population densities are comparatively high (Hofmeyr, 2009).
Range and Habitat
Extending from southern and western South Africa northward into southwestern Namibia, the range of the angulate tortoise comprises four communities of flora and fauna known as biomes. About 90% of the species' range occurs in southern and western South Africa, while the remaining 10% is in Namibia.
According to M. D. Hofmeyr, the species lives in areas of "low annual rainfall (less than 100 to 600 millimeters)," which converts to less than 4 to 24 inches. Rainfall in the southernmost portions of the range may reach 1,000 millimeters (39 inches) in a given season. Summers vary in temperature from mild to hot. Rainfall varies from seasonal (winter only in Mediterranean ecoregions) to year-round (Hofmyer, 2009). With the exception of the Albany Thickets, these biomes are comparatively arid habitats.
The southern African biomes which C. angulata inhabits include Fynbos, Albany Thicket, Succulent Karoo, and Nama Karoo. The following are based on Hofmyer's brief descriptions of each biome in Chelonian Research Monograph No. 5 published in 2009.
Based on an Afrikaans word meaning "fine-leaved," the term fynbos refers to a fire-prone shrubland that may be sparsely or densely vegetated. The dominant evergreen flowering shrubs of the fynbos, members of the heather family (Ericaceae), have small, needle-like or scale-like leaves. These shrubs and perennials are generally adapted to poor soils and arid conditions. The fynbos biome is also inhabited by many shrubs in the aster or daisy family (Asteraceae). Grass-like, perennial restios and other grasses add to the understory flora of the fynbos.
Dense, comparatively lush woodland regions located in the Albany region of the Eastern Cape of South Africa, the Albany thickets offer milder, more humid microclimates than other angulate tortoise biomes.
On the hot, open plains of the Albany thickets, the flora consists of sparse, semi-succulent and thorny species that tend to be fire-prone. Mountain and river valleys offer some respite from the summer heat, their succulent, thorny vegetation growing more densely with an understory of small-scale succulents and ground-dwelling creeping species. Tending to favor the more open plains, angulate tortoises are less likely to occupy the densest thickets.
According to the World Wildlife Fund for Nature, the Succulent Karoo ecoregion of South Africa and Namibia is a biodiversity hotspot with the greatest amount of succulent-plant diversity in the entire world. Approximately one-third of the world's 10,000 succulent species grow in the shrublands of the Succulent Karoo. Intermingled with succulents of all sizes are annuals, grasses, and geophytes (plants growing from bulbs, corms, rhizomes, etc.,) [Hofmeyr, 2009] Precipitation occurs mainly in winter in the Succulent Karoo, and extended droughts are rare. Rainfall is augmented by dew and heavy fog, both of which regularly form over this biome (Cowling).