Lemurs reveal clues to ancient Asian roots

Bug-eyed primate cousins of monkeys and apes, lemurs currently live in the wild

only on the African island of Madagascar. About 30 million years ago, however, a

diminutive lemur species inhabited what is now central Pakistan, a new fossil find

suggests.

The handful of teeth unearthed in Pakistan’s Bugti Hills represents the oldest

known lemur, contends an international team led by paleontologist Laurent Marivaux

of Université Montpellier in France. This discovery raises the possibility that

lemurs originated in southern Asia, not in Africa as many investigators have

assumed.

Only further fossil finds on both continents will unravel the evolutionary roots

of so-called strepsirrhine primates, which consist of lemurs and their close

relatives the lorises, the scientists conclude in the Oct. 19 Science. “The time

has come for the Asian scenario to receive more serious attention,” Marivaux says.

In sediment previously dated at approximately 30 million years old, researchers

found 18 teeth from the ancient lemur species, which they dubbed Bugtilemur

mathesoni. They argue that the shape of these specimens indicates that Bugtilemur

bore an evolutionary relationship to the modern dwarf lemur.

Crucial elements of the comblike set of teeth that juts from the lower jaw of

living lemurs and lorises appear in Bugtilemur, the researchers hold. For

instance, a thin, flattened fossil tooth with a scoop-shaped inner surface

resembles the lower canine tooth of today’s strepsirrhines, they say. Moreover,

Bugtilemur’s cheek teeth display unusual features, such as a triangular shape and

midtooth indentations, which also are found in the modern dwarf lemur.

“This is pretty compelling evidence for the earliest strepsirrhine in the fossil

record,” remarks D. Tab Rasmussen of Washington University in St. Louis. “Overall,

the teeth look like those of a primitive mouse lemur or dwarf lemur.”

The discovery of teeth from this ancient primate intensifies the mystery over when

and how lemurs reached Madagascar, Marivaux’s team notes.

Geological studies indicate that around 88 million years ago, Madagascar broke off

from the Asian mainland at what is now India. Yet several genetic analyses of

living primates suggest that the first lemurs evolved about 62 million years ago,

and direct ancestors of modern lemurs originated between 46 million and 38 million

years ago.

If those estimates prove accurate then ancient lemurs had to cross a water barrier

to reach Madagascar. Some researchers theorize that a few African lemurs floated

to Madagascar on thick clumps of vegetation.

In contrast, a 1998 genetic analysis concluded that lemurs and lorises originated

about 87 million years ago. If that estimate bears out, lemurs may have inhabited

Madagascar before it separated from the mainland, Marivaux says.

The new find also plays into an ongoing debate over whether the earliest primate

ancestors of monkeys, apes, and people evolved in Africa, as researchers have long

thought, or in eastern Asia (SN: 11/11/95, p. 309).

Scientists who study ancient primates are intrigued by the new find but emphasize

that it remains unclear how lemurs and lorises evolved.

The discovery of lemur teeth from so long ago in Pakistan doesn’t establish that

lemurs initially inhabited southern Asia and then moved on to Africa, Rasmussen

says. Previous fossil evidence shows that, at the time Bugtilemur lived, the same

species of tarsiers and other small mammals inhabited both Africa and Asia, he

points out.

Gregg F. Gunnell of the University of Michigan in Ann Arbor cautions that even

though Bugtilemur’s teeth look like those of modern lemurs in some respects, in

other respects they resemble those of a separate group of ancient primates called

adapids.

Says Gunnell, “This is a very important find that raises new questions about the

origin of strepsirrhines.”