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Madagascar's Lemurs
by Ian Tattersall
Ian Tattersall is a paleontologist and primatologist who has
worked extensively on the living and subfossil lemurs of
Madagascar as well as on a range of problems in early primate
and human evolution. Curator and chairman in the department of
anthropology of the American Museum of Natural History,
Tattersall is especially interested in the integration of
evolutionary theory with the fossil record. He has also served
as curator for several major exhibitions at the museum.
Reprinted with permission from
Scientific American,
January 1993
From dense rain forests to broad coastal plains, from deciduous
thickets to desert, Madagascar offers an extraordinary range of
environments. These habitats harbor an equally extraordinary
primate fauna that shows more clearly than any other what our
own primate ancestors were like early in the Age of Mammals,
approximately 50 million years ago.
These animals are the lemurs, Madagascar's dominant mammals. Why
they are there is not entirely clear. The story used to be that
the 1,000 mile-long Madagascan minicontinent had simply
preserved (in somewhat impoverished fashion) an archaic fauna
that was marooned on it when Madagascar separated from the
African mainland and drifted out to sea. In many ways the
island's living "lower" primates more closely resemble the
primates of the Eocene epoch (about 57 to 35 million years ago)
than they do the "higher" primates dominating the tropical
continents today. That fact was taken to imply that the
separation had occurred in the Eocene or thereabouts.
But we now know that Madagascar began its journey away from
Africa as much as 165 million years ago, when the dinosaurs
ruled and the only mammals were tiny and vaguely shrewlike.
Moreover, the island appears to have reached its present
separation of roughly 250 miles from Africa some tens of
millions of years before the great diversification of the
mammals and thus well before today's familiar groups such as the
primates, bats and rodents came into existence.
For land-bound latecomers such as primates, then, the only
possible means of access to Madagascar was by "rafting":
floating across the Mozambique Channel from Africa on matted
tangles of vegetation. Arriving thus, the ancestral lemurs would
have found an incredible wealth of ecological opportunities on
an island that is only slightly smaller than Texas and
topographically, climatically and ecologically much more
diverse.
 The island of Madagascar looks rather like a giant left
footprint in the sea, its long axis oriented more or less
north-south. It extends from within 12 degrees of the equator
all the way to the southern subtropical zone. Its eastern side
presents a steep escarpment to the prevailing easterly winds;
here heavy rainfall year-round supports a dense growth of rain
forest. To the west, a rugged central plateau slopes more gently
to broad coastal plains that become drier toward the south.
Moist forests in the northwest give way to deciduous forests and
thickets. These in turn yield in the far south to an
extraordinary desert-adapted flora in which as many as 98
percent of the species are unique. Add to these major regions a
host of local microclimates and secondary physiographic
features, and you have an unparalleled assortment of
environments for forest-living mammals to exploit.
No one knows what the range of habitats was in Madagascar at the
remote time when primates first arrived or what lived in those
habitats; the fossil record is simply lacking. What is certain,
though, is that the primates flourished and that by the time
human beings arrived under 2,000 years ago the island was home
to at least 45 lemur species. These primates ranged in body size
from the two-ounce mouse lemur, Microcebus, to the 400-pound
Archaeoindris, a match for a large gorilla.
Each of the lemur species was a lower primate, belonging (with
the bush babies, pottos and lorises) to the primate suborder
Strepsirhini. We, on the other hand, are higher primates,
belonging (with the monkeys and apes) to the suborder
Anthropoidea. (There is no consensus about which group the tiny
and enigmatic tarsier of Southeast Asia belongs to.) The
distinction between lower and higher primates is in fact a
rather archaic concept that is now going out of fashion, but it
is a convenient one to use here.
The higher primates appeared on the evolutionary scene much
later than did the lower primates, from one of which they
presumably evolved toward the end of the Eocene. Madagascar's
lemurs and their continental cousins have much in common with
 Eocene forms, retaining a suite of physical characteristics that
have been lost among higher primates. But only in Madagascar do
we still find lower primates that are diurnal, or active during
the day. Virtually all modern higher primates are diurnal, and
if anything in paleontology is certain, it is that all
anthropoids are descended from a diurnal common ancestor. So if
we wish to find analogies to our remote Eocene ancestors, we
must turn to the primates of Madagascar.
Modern lower and higher primates are distinguished from one
another by a number of structural features, most significantly
in their nervous systems and sense organs. The lower primates
have much smaller brains relative to body size than do higher
primates. They also differ in the development of the association
areas, which govern the transfer of information between the
various brain centers.
The balance between the senses of vision and smell also differs.
Although the eyes of lower primates are quite forward-facing,
the left and right visual fields do not overlap as much as they
do in higher primates. This arrangement limits depth perception
to the central part of the field of view. And whereas it is
natural that the nocturnal lower primates lack color-sensitive
cone cells in their retinas, what little is known about visual
discrimination in the diurnal lemurs suggests that their color
vision is at best limited.
As for the sense of smell, the lower primates have roomier nasal
cavities than do higher primates, with more complex internal
structures. Living lower primates retain the primitive mammalian
rhinarium, or "wet nose." It is part of a system for the
transfer of particles to the nasal cavity, where they are
analyzed by an organ that is, at most, vestigial in most higher
primates.
Many lower primates (but only a few South American monkeys among
the higher primates) have scent glands that exude substances
used to "mark" the environment. This process is important in
communication between individuals. Visual cues are less
important; the faces of lower primates lack the musculature
needed to produce the complex expressions through which higher
primates convey their states of mind.
 Living primates in general have lost the primitive claws that
enabled the first pre-Eocene primates to scale trees without the
ability to grasp. In their stead is a thumb, shifted away from
the other digits, that is at least to some extent opposable to
them, and sensitive tactile pads on the fingertips, which are
backed by flat nails. This fundamental change has consequences
that extend far beyond locomotion as well as into manipulative
abilities. But whereas higher primates generally manipulate
objects using the thumb in opposition to the other digits,
lemurs tend to pick things up with the whole hand. An item held
in this way is then more likely to be sniffed rather than
inspected visually and turned in the fingers for further
examination.
Both the lower and the higher primates are, of course, extremely
diverse groups, whose members represent myriad variations on the
themes outlined above. Nevertheless, the lower primates are
obviously more primitive than the higher primates (with respect
to the body systems discussed) in the sense that they more
closely resemble the ancestor from which both modern groups
 emerged. Although fossils are limited to bones and teeth, they
reveal clearly that in the Eocene primate brains were even
smaller in relation to body size than are those typical of
modern lemurs and that the visual sense had not achieved the
total domination over olfaction we see in today's higher
primates. Eocene primate hands and feet were certainly capable
of grasping but could probably manipulate objects no more
precisely than lemurs do at present. In other words, as
functioning organisms, Eocene primates were probably not too
different from today's lemurs. They were certainly close enough
so that by studying the lives of lemurs we can glimpse something
of the Eocene behavioral potential from which our vaunted human
capacities ultimately arose.
Not until the 1960s did information about the behavior of lemurs
begin to be available from field studies in Madagascar. The
results of those studies have been increasingly at odds with
earlier anticipations. For example, as long as it was possible
to think of "the lemur" as a general ancestral model, the
expectation, if any, was simple: lemurs would show a set of
relatively stereotypical behavior patterns, similar to those
exhibited by early primates and from which the higher primates
had managed to emancipate themselves. Yet perhaps the most
remarkable revelation of the field studies is how diverse the
lemurs are in their ways of life.
Of course, certain predictions from anatomy were indeed borne
out. Olfactory marking, using urine and feces as well as the
secretions of specialized glands, has been shown to be a
significant component of lemur behavior. To judge by its wide
occurrence among mammals, such marking is an ancient behavior,
and few would question its importance in communication among
Eocene primates.
Lemurs also turn out, as expected, to have a tendency to explore
their environments with their noses to choose ripe fruit, for
example, by smell rather than by appearance. Undoubtedly, then,
olfaction is of the greatest importance to members of all five
living families of lemurs, as it was to their Eocene precursors,
and much more so than it is to most higher primates. But does
the reverse apply to vision? Anyone who has watched a sifaka
lemur hurtle through the forest would conclude that the animal
is hardly handicapped by its lack of a higher primate's visual
system.
Lemurs, in fact, turn out to be as diverse as or even more so
than the higher primates in most aspects of their behavior and
ecology. Their diets, for instance, consist of much the same
items as those consumed by the higher primates: fruit, flowers,
leaves, buds and insects. But feeding on nectar, which is
unusual in higher primates, is being increasingly noted. As a
whole, lemurs tend to be dietary generalists, but some at least
are highly specialized for example, the bamboo lemurs. Many of
them concentrate not just on bamboo but on particular parts of
bamboo plants. Indeed, individuals of the species Hapalemur
aureus, weighing only a couple of pounds each, daily eat shoots
containing enough cyanide to kill half a dozen humans.
Similarly, lemurs occupy nearly all of the vegetational habitats
exploited by higher primates, from rain forest to arid brush.
Again, whereas almost all higher primates are diurnal, some
lemurs are nocturnal, others diurnal and yet others "cathemeral,"
spreading their activity fairly evenly between daylight and
darkness.
The range of types of social organization among lemurs is
enormous. Some lead more or less solitary lives, in which small
female ranges are overlapped by larger male ones. In certain
species, adult pairs rear immature offspring, whereas in
others, small groups consist of just a few adults of each sex.
And still other species live in fluid groups or in more stable
larger units that contain a couple of dozen individuals or more.
Within these broad categories, there are still further
variations. What is perhaps most surprising is that even within
the same species, substantial variation in social organization
may be found from place to place. What seems to be most
significant is that even though lemur brains tend to be smaller
than those of higher primates, at least some lemurs display the
complex sociality we usually associate with the higher primates.
The picture that is therefore beginning to emerge of the
behavioral variety of the lemurs has important implications for
the understanding of our own Eocene ancestors. Despite the
retention of such primitive behavioral traits as olfactory
marking, the wide variety suggests that from the beginning, well
before the increase in brain size that we associate with the
higher primates today, primates showed a behavioral flexibility
and adaptability that belie the inference most people would draw
from the description of these early forms as "primitive." It
seems to me that this is the essential evolutionary heritage of
our order, something far more important than any of the anatomic
characteristics to which we are wont to draw attention. As
higher primates ourselves, we tend to look at the lemurs and ask
why they did not evolve further in our direction. But in doing
this, we are missing the critical point that, as a whole, the
lemurs have actually inherited from their Eocene ancestors, as
we have from ours, the most significant primate characteristic
of all.
Looking at this picture from another perspective, it is
certainly clear that the lemurs had no need of higher primate
physical characteristics to make full use of the varied
ecological opportunities that Madagascar offered them. Perhaps
this point is emphasized most dramatically by considering the
full range of lemur species that existed on Madagascar when
humans first arrived there. The present range is impressive
enough: at the small end is the tiny two-ounce mouse lemur and
at the large end, the 15-pound babakoto. But in its pristine
state, the island was home to a spectrum of primate types that
equals, if it does not surpass, the entire variety achieved by
anthropoids in the rest of the world.
Late in the 19th century, excavations at sites in the central
plateau of Madagascar began bringing to light the subfossil, or
partially fossilized, remains of large-bodied extinct lemurs
that were clearly not of great age. We know of at least 15
species of subfossil lemurs, belonging to eight or possibly more
different genera. All of them are larger than any surviving
lemurs. The same pattern of large body size is found among the
nonprimate members of the subfossil fauna, including the
"elephant bird," Aepyornis maximus (the largest bird that ever
lived, possibly weighing almost half a ton), the pygmy
hippopotamus and a giant tortoise.
A long series of studies has revealed an astonishing array of
locomotor and positional behaviors among the subfossil lemurs.
Even by themselves, the living lemurs show a great variety of
such behaviors, ranging from the rapid, scurrying quadrupedal
motion of the tiny Microcebus to the spectacular leaping of the
long-legged indrid lemurs (sifakas, babakotos and the like). It
cannot really be said that any of the living lemurs is excluded
from any part of the forest environment by its anatomic
locomotor specializations, but it is generally true that most
species avoid spending much time on the ground. The only notable
exception is the ringtailed lemur, Lemur catta.
Among the extinct lemurs, on the other hand, was a group that
was clearly adapted for life on the ground. This is the family
Archaeolemuridae, containing the two medium-sized genera
Archaeolemur and Hadropithecus. Laurie R. Godfrey of the
University of Massachusetts at Amherst (the source for all the
estimates of subfossil body weight presented here) has estimated
that the various archaeolemurid species weighed between 35 and
55 pounds.
These lemurs were rather powerfully built, short-legged
relatives of the indrids, with highly specialized teeth.
Clifford J. Jolly of New York University has compared them,
respectively, with two African higher primates, the common and
gelada baboons. The common baboon is an extremely adaptable
form, at home in woodlands and deciduous forests as well as in
the savanna habitats in which it is so familiar. The gelada
baboon is specifically adapted to the treeless Ethiopian
highlands, and virtually all its food is derived from
terrestrial sources. Both the dentition and what is known of the
body skeleton of Hadropithecus suggest strongly that this lemur
had similar dietary and habitat preferences.
Another extinct indrid relative showed a totally different set
of adaptations. For analogues, one must look well beyond the
primates. Palaeopropithecus comprised at least two species with
a weight range of perhaps 90 to 130 pounds. Ross MacPhee, my
colleague at the American Museum of Natural History, has
analyzed a substantially complete skeleton recovered in northern
Madagascar a few years ago and concluded it was a generally
slow-moving and somewhat slothlike arboreal hanger, built for
flexibility rather than strength. Its even larger relative
Archaeoindris (probably more than 400 pounds) is poorly known,
but Martine Vuillaume-Randriamanantena of the University of
Madagascar believes it was probably a terrestrial quadruped
somewhat like the extinct ground sloths of the New World. Both
of these forms had specializations of the skull, particularly of
the nose area, that are unmatched among living primates.
We also have to look outside our own order to find an analogue
to the best-known subfossil lemur, Megaladapis. The three
species, ranging in weight from about 90 to 170 pounds, have
been described by Alan C. Walker of the Johns Hopkins School of
Medicine as closest in locomotion to the marsupial koala of
Australia. Like the koala, these lemurs would have climbed
slowly, presumably preferring vertical supports, and they had
limited leaping capabilities. A number of specializations of the
skull may have compensated for such locomotor limitations. They
would have allowed the animal to feed in a large radius from a
single sitting position.
The best known of the sites that have yielded extinct lemurs is
Ampasambazimba in Madagascar's central highlands. The 14 primate
species (including both extinct and surviving lemurs) whose
bones have been recovered there compare favorably in abundance
with the species at any other place in the world where primates
are found. Yet Ampasambazimba is in the middle of what is now an
essentially treeless plateau. How does it boast this rich and
heterogeneous forest-living fauna?
Studies dating from early in this century seemed to have the
answer. Before the advent of humans, the argument goes,
Madagascar was essentially fully forested. The fact that forest
had survived only in patches was attributed to the propensity of
the early settlers to burn off vast areas of forest to provide
grazing for cattle and land for agriculture. Indeed, the process
is still only too evident.
Following this argument, loss of habitat must have been at least
a major influence in the disappearance of Madagascar's large
birds and mammals. There was also a selective aspect of this
extinction: the lemurs known to have become extinct were large
bodied and thus of the greatest interest and vulnerability to
hunters. Presumably, they also reproduced more slowly than the
smaller forms that have survived. The case for a combination of
direct and indirect human activity as the agent of extinction
seems compelling.
Climatic change has also been promoted as an agent of
extinction, initially because many subfossil sites consist of
dried-up lakes or marshes. As a total explanation of the
extinctions, drying was never completely convincing. Still,
interest in a possible climatic effect has been revived recently
by the demonstration that some of the grasslands of Madagascar's
center are of long (and certainly prehuman) standing.
Analyses of lake cores by David A. Burney of Fordham University
have underscored the fact that, like every other region of the
earth, Madagascar has undergone climatic fluctuations over the
past few thousand years. At the end of the last ice age some
10,000 years ago, Madagascar's forests were apparently just
beginning to recover from a period of contraction. It is
therefore hardly surprising that the central highlands were not
fully forested by the time Madagascar's first people arrived.
 Climatic stress and the consequent reduction and redistribution
of forests thus constitute one potential factor in the
disappearance of the subfossil fauna of Madagascar. But it is
clear that in that land as elsewhere, periodic disturbances of
this kind have occurred throughout time. The ancestral lineages
of the extinct lemurs obviously survived these earlier
vicissitudes, and there is no reason to believe that on their
own the most recent (rather mild) round of climate changes
should have had a fatal effect on several lineages
simultaneously. This is especially true when we consider that
most subfossil lemurs were probably ecological generalists.
Megaladapis, Palaeopropithecus and Archaeolemur, among others,
lived in environments ranging from humid to arid and were
clearly highly adaptable in terms of choice of habitat. Hence,
something other than simply another cycle of disturbance of
natural habitat must be invoked to explain the disappearance of
the giant lemurs. Only one truly novel factor presents itself:
Homo sapiens.
To talk of the "extinction event" of the large-bodied lemurs
implies a process that has ended. That is not so. The extinct
and living lemurs form part of a single process that is
continuing. The smaller, fleeter lemurs have survived so far,
but they are themselves under increasing pressure from an
expanding human population. The toll of hunting increases as
human numbers and the use of more sophisticated weapons do.
Another important consideration is the population movements that
tend to erode the local beliefs that, in certain places, have
traditionally protected various lemur species.
More worrying yet is destruction of habitat, principally by
slash-and-burn agriculture but also by the cutting of trees for
fuel and by commercial logging. The largest continuous forest
tract in Madagascar lies along the island's humid eastern
escarpment. By analyzing historical documents and satellite
images, Glen M. Green and Robert W. Sussman of Washington
University have shown that 66 percent of the area covered by
this forest at the turn of the century had been denuded by 1985.
They estimate that within another 35 years only the steepest
slopes of the escarpment will still bear trees. In the flatter
western and southern regions of the island, the rate of
disappearance of forest is probably faster.
Such pressures have existed for many decades. In the 1920s the
colonial authorities in Madagascar set up one of the world's
first systems of natural reserves. But as one of the world's
poorest countries, Madagascar, despite its government's genuine
concern, cannot afford to police these reserves adequately or,
in some cases, at all. Fortunately, in recent years the island
has attracted the attention of the international conservation
community. The country figured recently in one of the first
"debt for nature" swaps, in which foreign debt is reduced in
exchange for the protection of natural areas.
It is, of course, the real and immediate needs of desperately
poor local communities that are being met by most of the forest
destruction. In many cases, large-scale agreements on
conservation have yet to devolve from the higher governmental
sphere to actual projects on the ground. But as they do, one can
hope for the stabilization and perhaps even for the long-term
improvement of Madagascar's environmental situation.
Meanwhile the lemur populations continue to dwindle. It is
tragic to see any part of the world's biodiversity disappear,
but the tragedy is particularly acute in the case of
Madagascar's lemurs, which still have so much to teach us about
our own past.
Climatic stress and the consequent reduction and redistribution
of forests thus constitute one potential factor in the
disappearance of the subfossil fauna of Madagascar. But it is
clear that in that land as elsewhere, periodic disturbances of
this kind have occurred throughout time. The ancestral lineages
of the extinct lemurs obviously survived these earlier
vicissitudes, and there is no reason to believe that on their
own the most recent (rather mild) round of climate changes
should have had a fatal effect on several lineages
simultaneously. This is especially true when we consider that
most subfossil lemurs were probably ecological generalists.
Megaladapis, Palaeopropithecus and Archaeolemur, among others,
lived in environments ranging from humid to arid and were
clearly highly adaptable in terms of choice of habitat. Hence,
something other than simply another cycle of disturbance of
natural habitat must be invoked to explain the disappearance of
the giant lemurs. Only one truly novel factor presents itself:
Homo sapiens.
To talk of the "extinction event" of the large-bodied lemurs
implies a process that has ended. That is not so. The extinct
and living lemurs form part of a single process that is
continuing. The smaller, fleeter lemurs have survived so far,
but they are themselves under increasing pressure from an
expanding human population. The toll of hunting increases as
human numbers and the use of more sophisticated weapons do.
Another important consideration is the population movements that
tend to erode the local beliefs that, in certain places, have
traditionally protected various lemur species.
More worrying yet is destruction of habitat, principally by
slash-and-burn agriculture but also by the cutting of trees for
fuel and by commercial logging. The largest continuous forest
tract in Madagascar lies along the island's humid eastern
escarpment. By analyzing historical documents and satellite
images, Glen M. Green and Robert W. Sussman of Washington
University have shown that 66 percent of the area covered by
this forest at the turn of the century had been denuded by 1985.
They estimate that within another 35 years only the steepest
slopes of the escarpment will still bear trees. In the flatter
western and southern regions of the island, the rate of
disappearance of forest is probably faster.
Such pressures have existed for many decades. In the 1920s the
colonial authorities in Madagascar set up one of the world's
first systems of natural reserves. But as one of the world's
poorest countries, Madagascar, despite its government's genuine
concern, cannot afford to police these reserves adequately or,
in some cases, at all. Fortunately, in recent years the island
has attracted the attention of the international conservation
community. The country figured recently in one of the first
"debt for nature" swaps, in which foreign debt is reduced in
exchange for the protection of natural areas.
It is, of course, the real and immediate needs of desperately
poor local communities that are being met by most of the forest
destruction. In many cases, large-scale agreements on
conservation have yet to devolve from the higher governmental
sphere to actual projects on the ground. But as they do, one can
hope for the stabilization and perhaps even for the long-term
improvement of Madagascar's environmental situation.
Meanwhile the lemur populations continue to dwindle. It is
tragic to see any part of the world's biodiversity disappear,
but the tragedy is particularly acute in the case of
Madagascar's lemurs, which still have so much to teach us about
our own past.
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