Evolution And History

Living Primates 67

Tarsiers

Outwardly, tarsiers resemble lemurs and lorises. Molecu-

lar evidence, however, indicates a closer relationship to

monkeys, apes, and humans. The head, eyes, and ears of

these kitten-sized arboreal creatures are huge in propor-

tion to the body. They have the remarkable ability to turn

their heads 180 degrees, so they can see where they have

been as well as where they are going. Their digits end in

platelike adhesive discs.

Tarsiers are named for the elongated tarsal, or foot

bone, that provides leverage for jumps of 6 feet or more.

Tarsiers are mainly nocturnal insect eaters and so oc-

cupy a niche that is similar to that of the earliest an-

cestral primates. In the structure of the nose and lips

and in the part of the brain governing vision, tarsiers

resemble monkeys.

rodents and insectivores, with short
pointed snouts, large pointed
ears, and big eyes. In the
anatomy of the upper lip
and snout, lemurs and lor-
ises resemble nonprimate
mammals in that the up-
per lip is bound down to
the gums, thus limiting
their range of facial ex-
pression. The naked skin
on the nose around the
nostrils is moist and split,
which facilitates a keen
sense of smell. Most also
have long tails, with that
of a ring-tail lemur somewhat like the tail of a raccoon.
Lemurs and lorises have typical primate “hands,” al-
though they use them in pairs, rather than one at a time.
Their fingers and toes are particularly strong. Sensitive
pads and flattened nails are located at the tips of the fin-
gers and toes, although they retain a claw on their second
toe, sometimes called a grooming claw, which they use
for scratching and cleaning. Lemurs and lorises possess
another unique structure for grooming: a dental comb
made up of the lower incisors and canines that projects
forward from the jaw and that can be run through the
fur. Behind the incisors and canines, lemurs and lorises
have three premolars and molars, resulting in a dental
formula of 2-1-3-3.
Lemurs and lorises have scent glands at their wrists,
under their arms, and/or in their anal regions that they
use for communication. Individuals leave smelly mes-
sages for one another by rubbing their scent glands on
tree branches or some other fixture of the environment.
Through such olfactory clues, lemurs and lorises can rec-
ognize distinct individuals within their own group as well
as pinpoint their location and physical state. They also
use scent to mark their territory, thus communicating to
members of other groups.
The hind legs of lemurs and lorises are longer than
their front legs, and when they move on all fours, the
forelimbs are in a palms-down position. Some species
can also move from tree to tree by vertical clinging and
leaping. First they hang onto the trunk of one tree in an
upright position, with their long legs curled up tightly
like springs and their heads twisted to look in the direc-
tion they are moving. They propel themselves into the
air, do a “180,” and land facing the trunk on their tree
of choice.
With their distinctive mix of characteristics, lemurs
and lorises appear to occupy a place between the anthro-
poid primates and insectivores, the mammalian order that
includes moles and shrews.

With their large eyes, tarsiers are well adapted for nocturnal life. If

humans possessed eyes proportionally the same size as tarsiers rela-

tive to the size of our faces, our eyes would be approximately the size

of oranges. In their nocturnal habit and outward appearance, tarsiers

resemble lemurs and lorises. Genetically, however, they are more closed

related to monkeys and apes, causing scientists to rework the suborder

divisions in primate taxonomy to reflect this evolutionary relationship.

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