Prosimians are widely distributed in the remaining tropical forests of Africa, Asia and Madagascar. A group that includes lemurs, lorises and galagos, they may be the most ancient of living primates, with an evolutionary history reaching back at least 65 million years, into the last days of the dinosaurs.
The name “pro-simians” means “before the monkeys,” and although today’s species are by no means primitive or unchanged, modern prosimians retain many of the physical features that were common to the earliest true primates. The typical prosimian skull has large eye sockets, a relatively small braincase, an elongated snout and adaptations for well-developed senses of hearing and smell.
Almost all prosimians have comb-like projections on their lower front teeth, used for grooming their fur. They also share a specialized grooming claw on the second toe of each hind foot. Their narrow snouts support a moist and finely sensitive nose, and their eyes have a tapetum lucidum – a reflective layer behind the retina that captures stray light and enhances their vision at night.
This catlike visual ability, together with their heavy reliance on scent, parallels the nocturnal lifestyle of the original primates, and perhaps unfairly paints the prosimians as primate relics or living fossils. Despite their deep history, the prosimians are as diverse and ecologically dynamic as any other primates. Until very recently, by virtue of the lemurs of Madagascar, the prosimians encompassed a greater range of body size and form than any of their anthropoid cousins.
ACTIVITY: Locate these primates on our Interactive Primate Tree.
Tarsiers: Prosimian or Anthropoid?
The tarsiers of Southeast Asia are the exception to the prosimian norm – they are neither completely prosimian nor completely anthropoid. Tiny predators, with owlish eyes and a whip-like tail, the tarsiers share many features with the prosimians: they are nocturnal, with grooming claws and a well-developed sense of smell.
But tarsiers have no tooth-combs and their eyes lack the tapetum lucidum. These and other characteristics suggest they are distinct from the prosimians. They are the only completely carnivorous primates, feeding on small vertebrates and arthropods.
Loriformes: Galagos & Lorises
The loriformes – galagos and lorises – are widespread across Africa and Southeast Asia, are entirely nocturnal, and evidently have been so throughout their long history. Some species, in particular many galagos, are not in danger of extinction. Many lorises, however, are typically slow-moving and have small home ranges, allowing for easy capture. These creatures rely on tropical forest habitats which continue to be diminished by timber and mining interests.
The lemurs of Madagascar are strikingly different from their loriform cousins. They have evolved in isolation on their island continent and many species have become diurnal (active during the day) as well as cathemeral (active both day and night).
This great latitude in lifestyle has given rise to a remarkable tapestry of adaptations – from diet to habitat to body size and reproduction, as well as complex and varied social systems. Lemurs are as keenly attuned to scent as other prosimians, and they typically mark their territories by urine-washing or by secretions from specialized glands, which may be on the wrists, the throat or the head.
IN DEPTH: Ring-tailed lemurs use these glands in mating rituals. Learn how >>
But the lemurs that live in the forests of Madagascar today, while magnificent in their variety, are only the surviving remnants of a spectacular array of prehistoric species, which only a few thousand years ago presented an unequalled spectrum of primate diversity.
The lemurs of ancient Madagascar expanded the possibilities of primate body form as never before, diversifying into species with a unique fusion of traits. Some of the most surprising included:
• Stub-tailed lemurs that lived like sloths, suspended below the branches;
• Prehensile-lipped lemurs that moved and fed like giant koalas; and
• Giant, ground-dwelling lemurs nearly the size of today’s gorillas.
Some of these prehistoric lemurs may have gone extinct from climatic shifts in the recent past. But others survived until only a few centuries ago, and their disappearance may have coincided with the arrival of humans to Madagascar, and the subsequent deforestation of the island’s central plateau. It is no accident that the lemur species that went extinct were, without exception, the largest on the island – and thus the slowest and most tempting targets for newly arrived hunters.
Today the surviving lemurs are now recognized as a global conservation priority – found only in Madagascar, where more than 80 percent of the original forest has been fragmented or destroyed.
LEARN MORE: Get details about lemur species and listen to recordings of their calls.