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A handful of tiny teeth collected in the Bugti Hills of Pakistan represent the fossil remains of the earliest known lemur, say an international team of researchers in the 19 October issue of the journal Science.
They also represent something of a mystery, since today's lemurs--primate cousins to the monkeys and apes, with a tooth "comb" jutting from their lower jaw--live only on the island of Madagascar. Scientists had previously thought that Africa must have been the birthplace of lemurs, but the new find may turn heads towards a possible Asian origin instead.
The discovery of a lemur fossil on the Indian subcontinent was "totally unexpected," says Science author Laurent Marivaux of the Université Montpellier in France.
Dubbed Bugtilemur mathesoni, the 30 million year old lemur species provides an extremely rare glimpse into the evolution of strepsirrhine primates, which consist of lemurs and their close relatives, the lorises. Although the strepsirrhines are a diverse group, there is virtually no fossil record for lemurs, making their pre-Madagascar days a paleontological blank slate.
Marivaux, Jean-Jacques Jaeger of Université Montpellier, and colleagues analyzed anatomical features on Bugtilemur's teeth to determine where it fit into the primate family tree, concluding that it was most closely related to Cheirogaleus, the modern dwarf lemur on Madagascar. Bugtilemur and Cheirogaleus share a specialized dental pattern different from other living lemurs, including other members of the dwarf and mouse lemur family.
The close relationship poses a problem for primate researchers. Current evidence indicates that Madagascar and the Indian subcontinent broke away from each other around 88 million years ago, probably long before the origin of all lemurs (around 62 million years ago), and much longer before specialized lemurs like Cheirogaleus appeared (around 46-37 million years ago).
This suggests that some type of early lemur migration probably took place after the breakup of the two land masses, but that scenario presents another puzzle: which direction did the exodus take? The answer depends on where lemurs may have first evolved. Previous research suggested that Africa was the birthplace of lemurs and lorises, and that lemurs later migrated eastward to Madagascar, perhaps hitching a ride on rafts of floating vegetation to their current island home. But the appearance of a specialized, clearly recognizable lemur like Bugtilemur at such an early date raises the possibility of an Asian origin.
Teeth from several other new primate species, including some anthropoids--the ancestors to monkeys and apes--have been recovered from the Bugti Hills site along with Bugtilemur. These fossils, along with recent anthropoid discoveries in China, Myanmar, and Thailand should renew interest in Asia as a major center for primate origins, according to the Science study authors.
"The time has come for the Asian scenario to receive more serious attention, but I think that the paleontological solution to this enigma is still in the future," says Marivaux.
Bugtilemur was recovered from a site teaming with other aquatic and terrestrial fossil specimens. Fossilized tree parts, pollen, and fruit indicate that Bugtilemur lived in an environment that probably resembled a modern tropical forest. The nearby discovery of a Baluchitherium skeleton by the Science researchers also testifies to a formerly lush landscape. Baluchitherium was one of the largest land mammals that ever lived on Earth, weighing in at close to 20 tons.
"This amazing mammal probably ate more than a ton of leaves and other things per day, and shared the same paleoenvironment and paleoconditions with the minute Bugtilemur," says Marivaux.
Marivaux says that future fieldwork at Bugti Hills, the site of paleontological investigation for the last seven years, has been postponed by the recent terror attacks on the United States.
"At the moment, we are totally dependent on the effects of current events, but we actively continue to work with our Pakistani colleagues on these exciting discoveries."
The other members of the research team include Jean-Loup Welcomme, Grégoire Métais, and Stéphane Ducrocq at Université Montpellier, Ibrahim M. Baloch at the University of Balochistan, in Quetta, Pakistan, Pierre-Olivier Antoine at the Muséum National d'Histoire Naturelle in Paris, France, Mouloud Benammi at the Universidad Nacional Autonoma de Mexico, and Yaowalak Chaimanee at the Department of Mineral Resources, Bangkok, Thailand. This research was supported in part by Université Montpellier, the Muséum National d'Histoire Naturelle, the Fyssen, Leakey, Wenner-Gren, Singer-Polignac, Bleustein-Blanchet and Treilles Foundations.
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Science