A third species of Palaeopropithecus, an extinct group of large lemurs, has just been uncovered in the northwest of Madagascar by a Franco-Madagascan team. Dubbed Palaeopropithecus kelyus, this new specimen is smaller than the two species of these 'large sloth lemurs' already known and its diet made up of harder-textured foodstuffs. This discovery supports the idea of a richer biodiversity in recent prehistory (late Pleistocene and beginning of the Holocene).
Madagascar, where natural environments show a high level of endemism, is one of the last great biodiversity sanctuaries in the world. The island is home to a special group of primates, the lemurs. There are presently 15 genera and 71 species of these small mammals on Madagascar.
The genus Palaeopropithecus is a group of subfossil giant lemurs(2). Up until now, two species had been described: P. ingens (in 1898) and P. maximus (in 1903). Palaeopropithecus have very specific adaptations, notably for locomotion, as they moved from branch to branch using all four limbs, with their head downwards, in a similar way to today's South American sloths.
Recent discoveries by the MAPPM(1) on sites in northwest Madagascar have established the existence of a third species of Palaeopropithecus, which has been dubbed P. kelyus. Scientists have suspected the existence of this species for more than 20 years. P. kelyus, whose weight is estimated around 35 kg, is smaller than the two known Palaeopropithecus species, but is very large in comparison with the largest living lemur, the Indri, which weighs only 10 kg.
The other main difference of this new species is that its teeth are smaller. Its dental characteristics could be described from the P. kelyus subfossil maxilla fragment, showing a crista obliqua, a parastyle and a highly developed mesostyle. This morphology is reminiscent of the present day Propithecus genus. While other Palaeopropithecus must have fed on leaves and fruit, the differences in the teeth of P. kelyus suggest that this animal could chew much tougher foods (notably seeds) compared with the other two known species. P. kelyus was found in an area of northwest Madagascar (Boeny region, Mahajanga province) with the particularity of being situated between large bays and rivers. This topography could have isolated P. kelyus from the other two species of Palaeopropithecus, one of which lived more in the south or centre, and the other in the north of Madagascar.
In the ‘evolution laboratory' that Madagascar represents, the discovery of this third Palaeopropithecus contributes to our understanding of the subfossil fauna species. More broadly, such work also includes the study of the island's human population.
(1) The project ‘Mission archéologique et paléontologique dans la province de Mahajanga' (MAPPM) is a Franco-Madagascan collaboration between CNRS UPR 2147 (Dynamique de l'Évolution Humaine: Individus, Populations, Espèces) and UFR Mozea Akiba of Université de Mahajanga, funded by the Sous-direction de l'archéologie et de la recherche en sciences sociales of the French Ministry of Foreign and European Affairs, CNRS and Université de Mahajanga.
(2) Subfossils are species that died out during the historic or prehistoric eras and overlapped present-day species. Unlike classic fossils, their bones are not completely mineralised.
The results, currently available online, will be published in the Comptes Rendus Palevol (Académie des Sciences), July-August 2009.
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