Strepsirrhini (lemurs, lorises, and other primitive primates)

Primate taxonomy reflects the evolutionary relationship between different groups of primate species. Just like the cladograms we looked at in class, the different branches on the primate "family tree" represent species with shared, derived traits (synapomorphies). The first fork in the tree is the division between the Strepsirrhini and the Haplorhini.

How to tell a Strepsirrhini from a Haplorhini

The Strepsirrhini are the most primitive of the primates (note that in this context, "primitive" means "most like the ancestral primate species"). Strepsirrhini you may be familiar with include lemurs and lorises. The Strepsirrhini are different from the Haplorhini in several important ways:

Some of these traits you have seen in lab on the primate skulls. Some can only be seen in living animals. All of these traits represent derived traits in the Haplorhini that differentiate them from the Strepsirrhini.

Within the Strepsirrhini, there are a number of different taxonomic groups. For this class, we will only learn about two general categories of Strepsirrhini: Lemoriformes and Lorisiformes.

Lemoriformes

Lemoriformes is an infraorder that includes lemurs and aye-ayes. Their name literally means "lemur-shaped". All Lemuriforms have a toothcomb. They are quite diverse, but have the most primitive characteristics of any primates, including a better sense of smell (and poorer vision) than monkeys or apes.

Distribution:

Lemuriformes are only found on Madagascar and the Comoro Islands, where they face no competition from more advanced primates, like the ones living on the mainland of Africa.

Locomotion:

Most lemuriformes are quadrupedal, meaning they walk on four legs. This video shows a mouse lemur scampering on all fours across the tree-branches, as well as jumping from branch to branch.

Other lemuriformes move around primarily through clinging and leaping, a type of jumping between branches while keeping the body more or less vertical. It can be seen in this video of an Indri (a type of lemur).

A few lemuriformes even engage in some pretty spectacular bipedal hopping, as you can see in this video of sifakas. This is mostly seen in animals who normally cling and leap through trees, but need an alternative way to get around when they're on the ground.

Social Organization:

Lemuriformes live in a variety of social groups. Some live in large groups of males and females, old and young. Many, like the aye-aye are solitary, meaning they have their own territory and won't share with other members of their species. Others, like the indri live in small family groups. The wide variety of social organizations reflects the adaptive radiation of lemurs in Madagascar. They adapted to different niches in a variety of ways, including different social organizations. In general, though, lemuriformes have simpler social organization than other types of primates.

Active Time:

Many lemuriformes are nocturnal (active during the night). Often these species can be identified by their large eyes and ears, which are adaptations for getting around at night. Some are diurnal (active during the day).

Habitat:

Lemuriformes are found throughout Madagascar, in forests, rainforests, and even reeds along the shore. Although some lemuriformes spend a good deal of their time on the ground, most are arboreal, and spend almost all their time in the trees.

Diet:

Since lemuriformes adapted to a variety of different niches on Madagascar, they eat a variety of different foods. Many are insectivorous (their diet focuses on insects), but others focus on fruit, tree gum, leaves, or bamboo. None have been seen to hunt or to eat a significant amount of non-insect meat.

Lorisiformes

Like lemuriformes, the lorisiformes are an infraorder of primative primates. This group includes the lorises and galagos (the name literally means loris-shaped). Unlike lemuriformes, lorisiformes live on mainland Africa, as well as in southern Asia. They can co-exist with more advanced primates because they are nocturnal, so fill a different niche from monkeys and apes. (Only one species of Haplorhini is nocturnal, and it lives in South America). Like lemuriformes, they have a better-developed sense of smell than Haplorhini primates. Lorises, in fact, urinate on their hands in order to mark their territory as they travel across it. One distinguishing characteristic of the lorisiformes is their oddly shaped hand, which has a shortened second finger, a toilet claw, and a wide span to allow for a powerful hold on tree branches.

Distribution:

Lorisiformes are found in southern India, Sri Lanka, much of Southeast Asia, and the tropical regions of sub-Saharan Africa.

Locomotion:

Many lorisiformes are slow quadrupeds, like this slow loris. Others, however, are champion clingers and leapers, like the galago, who can leap up to 7 feet. As with other clingers and leapers, the galago often bounces when on the ground (where they are seldom found).

Social Organization:

Most lorisiformes are solitary, but some, like galagos, sleep in groups. Like lemuriformes, lorisiformes have more simple social organizations than Haplorhini primates.

Habitat:

Lemuriformes live in tropical rainforests and woodlands, although galagos are sometimes found in more open forests. They are almost entirely arboreal, spending little time on the ground.

Diet:

Different lemuriformes species have different diets. Many are insectivorous, but others, like the slow loris, are more omnivorous (they eat a variety of foods). Some even focus on fruit.

And here's your "oh for cute!" moment of the day: a video of a loris being tickled. Enjoy!