All the mammals of Madagascar are descended from four ancestral species that must have sailed there clinging to rafts of plant material, scientists believe.
Madagascar split from Africa 165-million years ago, and has been isolated from all other land by deep water for some 88-million years. Scientists have been mystified about the origins of the 100 or so unique terrestrial mammalian species that live there.
They belong to four main groups — carnivores, lemurs, rodents and tiny hedgehog-like insect eaters called tenrecs. New research now indicates that all evolved from four different kinds of ancestor that somehow survived the 400-kilometre sea journey from mainland Africa.
A team led by John Flynn, of the Field Museum of Natural History in Chicago, compared genetic variation of the seven living carnivorous mammal species on Madagascar with carnivores elsewhere.
The analysis showed that the Madagascar carnivores had a single common ancestor whose closest living relative was the African mongoose. An earlier genetic study by Anne Yoder, of Yale University in New Haven, Connecticut, showed that lemurs also shared a common ancestor.
By combining their data Flynn and Yoker worked out that the ancestral carnivore must have arrived 18-million to 24-million years ago, while the first lemurs turned up between 62-million and 66-million years ago.
The researchers have yet to date the arrival of the rodents or tenrecs, but Flynn believes they too are descended from a single species. The results were published in the journal Nature and reported by the magazine New Scientist.
Flynn said: ”Our research shows that all the species of Madagascar’s carnivora together represent a unique evolutionary branch formed by a significant one-time event. In fact, all 100 or so known species of terrestrial mammals native to Madagascar, which fall into four orders — carnivorans, lemurs, tenrecs and rodents — can now be explained by only four colonisation events.”
He believes the animals must have ridden on large clumps of plant material, as other creatures have over shorter distances. Three of the four groups go into hibernation or torpor when food and water are scarce, which could have helped them survive the sea voyage. – Sapa-DPA