Are Lemurs Monkeys? Where Lemurs Fit Among the Primates

Where do lemurs fit on the primate family tree?

Living primates fall into two main groups. The strepsirrhines include the lemurs of Madagascar, plus the lorises, pottos and galagos (also called bushbabies) of Africa and Asia. The haplorhines, or dry-nosed primates, include the tarsiers of Southeast Asia, all monkeys and all apes, including humans.

So a lemur is about as closely related to a monkey as it is to a chimpanzee or to us. The two lineages are thought to have split more than 60 million years ago. The word “prosimian”, which you may see in older books, was once used for lemurs, lorises, galagos and tarsiers together, but because tarsiers are closer to monkeys, most biologists now prefer the strepsirrhine and haplorhine split.

How are lemurs different from monkeys?

Several body features set lemurs apart. They are easiest to see on a close look at the face and feet of a species such as the ring-tailed lemur.

A wet nose. Lemurs have a rhinarium, a moist, hairless nose tip like a dog’s, connected by a groove to the upper lip. It helps them sense smells. Monkeys and apes have a dry, furry upper lip and nose.

A toothcomb. In most lemurs, the lower front teeth (four incisors and two canines) point forward and are packed closely together like the teeth of a comb. Lemurs use this toothcomb to groom fur and, in some species, to scrape sap or gum from bark. A small structure under the tongue, the sublingua, cleans hair out of the comb.

A grooming claw. Lemurs have flat nails on most fingers and toes, like other primates, but the second toe of each foot ends in a long claw used for scratching and cleaning the fur.

A reflective eye layer. Many lemurs have a tapetum lucidum, a mirror-like layer behind the retina that improves night vision and makes their eyes shine in torchlight. Monkeys lack it.

Smaller brains. Lemurs have smaller brains relative to body size than monkeys and apes, and they rely more on smell and less on sight than monkeys do.

Behavior that sets lemurs apart

Lemurs communicate heavily through scent. Many species carry scent glands on the wrists, chest or genitals and use them to mark branches and territory. Ring-tailed lemur males even hold “stink fights”, waving scent-soaked tails at rivals.

Female dominance is another striking trait. In many lemur species, females have priority over males for food and often lead the group, which is rare among monkeys and apes. Many lemurs also breed in very short, fixed seasons and can lower their metabolism to save energy. Dwarf lemurs are the only primates known to hibernate for months at a time.

Grooming looks different too. Monkeys part each other’s fur with their fingers and pick out debris, while lemurs groom with their toothcomb and tongue.

Why do lemurs look like monkeys?

Some lemurs do resemble monkeys at first glance, with long tails, grasping hands and forward-facing eyes. These shared features come from their common primate ancestry and from a life spent climbing in trees. Primates in general have grasping hands and feet, nails instead of claws on most digits, and good depth perception.

On Madagascar, lemurs evolved without competition from monkeys, which never reached the island. Over tens of millions of years they spread into roles that monkeys, squirrels and even woodpeckers fill elsewhere. The result is a remarkable range of forms, from tiny mouse lemurs weighing about 30 g (1 oz) to the indri, which can weigh around 9 kg (20 lb). Before people arrived, giant lemurs as large as a gorilla also lived on the island. How lemurs reached Madagascar in the first place is covered in Where do lemurs live?.

Lemurs, apes and monkeys compared

People often lump all primates with tails together as monkeys. In fact apes such as chimpanzees are not monkeys either, as explained in Are chimpanzees monkeys?. A simple way to remember the groups is:

• Lemurs: wet nose, toothcomb, grooming claw, only on Madagascar and the Comoros.
• Monkeys: dry nose, usually a tail, found in Africa, Asia and the Americas.
• Apes: dry nose, no tail, larger brains, found in Africa and Southeast Asia.

Are there “monkey lemurs”?

Some names cause confusion. The extinct giant lemurs known as “monkey lemurs” (such as Archaeolemur) are called that because their skeletons look somewhat monkey-like, but they were true lemurs. Likewise, flying lemurs or colugos of Southeast Asia are neither lemurs nor primates; they belong to their own small order of gliding mammals.