Lemurs reveal clues to ancient Asian roots
By Bruce Bower
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.”
