Madagascar is home to a unique primate assemblage that is found nowhere else. Having separated from all other land masses 88 mya (million years ago), evolution has occurred in isolation from mainland Africa and India. The Strepsirrhine ancestors of lemurs are thought to have emerged in or before the Eocene epoch (55-37 mya), and Strepsirrhines may have begun to colonize Madagascar as early as 80 mya, later evolving into what we now know as the lemurs of Madagascar (Yoder et al. 2003).
What is particularly amazing about the evolutionary history of lemurs is that their ancestors are thought to have rafted over to Madagascar on large clumps of floating vegetation. It is thought that the ancestors’ ability to enter torpor (a state of lowered physiological activity characterized by reduced metabolism, heart rate, respiration, and body temperature) offset the costs of food shortages they would have experienced rafting over to the island (Martin 1972, 2000).
How plausible is this scenario?
In a 2010 Nature article (Ali and Huber 2010) used new computer models of Eocene ocean currents that lends support to the rafting hypothesis. During the Eocene, currents were especially strong in the southwest Indian Ocean and Mozambique Channel, and had different directionality than the currents do today. Currents moved so fast (up to 20cm/s) that matted vegetation could have been transported from Africa to Madagascar in as few as 25 to 30 days. Further colonization from mainland Africa was cut off by the currents’ change into what they are today. Furthermore, the rafting hypothesis explains why none of mainland Africa’s larger mammals exist in Madagascar.
So, Madagascar existed untouched for millions of years giving rise to 101 species and subspecies of lemurs, 13 of which went extinct with the arrival of humans on the island over 2000 years ago…but that’s another story for another day.
Ali JR. and M Huber. (2010) Mammalian biodiversity on Madagascar controlled by ocean currents. Nature 463:653-656.
Martin RD. (1972) Adaptive radiation and behaviour of the Malagasy lemurs. Phil. Trans. R. Soc. Lond. B 264: 295-352.
Martin RD. (2000) Origins, diversity, and relationships of lemurs. Int. J. Primatol. 21:1021-1049.
Yoder AD, Burns MM, Zehr S, Delefosse T, Veron G, Goodman SM and JJ Flynn. (2003) Single origin of Malagasy carnivora from an African ancestor. Nature 421:734-737.