The Evolutionary Ecology of the African Pancake Tortoise Malacochersus tornieri (Siebenrock 1903): A Review and Synthesis Based Upon Current Knowledge
Keywords:
East Africa, crevice fauna, competition, tortoise predation, tortoise evolutionAbstract
The pancake tortoise Malacochersus tornieri (Siebenrock 1903) of East Africa is morphologically, behaviourally and ecologically unique among extant land tortoises of the family Testudinidae. Recent studies suggest it shares a common ancestor with the Indotestudo – Testudo group, but the selective pressures and evolutionary pathway that produced the single extant species, Malacochersus tornieri, are poorly understood. We propose that intense predation pressure and competition initiated the process of change from an ancestral, generalized tortoise form by driving Malacochersus into rocky areas and subsequently rock crevices, where predation and competition were reduced. This change in habitat led to rapid changes in morphology, ecology, and behaviour in order to better adapt to the crevice environment, and to enhance its safety within from predators. These changes in turn led to strict limits to the extent and duration of out-of-crevice activity. The changes in morphology also allowed greater mobility, agility, and speed to enhance safety when tortoises left their crevices to forage, mate, defecate, or colonize new habitats. Padlopers, an extant clade of small, southern African tortoises may provide insight into the pancake tortoise’s ancestral evolution toward its modern form, lifestyle, and reproductive characteristics. Both the pancake tortoise and padlopers also inexplicably display an unusually large amount of anomalous variation in scute and/or shell characteristics.
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