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| Earth on Jun 08, 2011

Lifeform of the week: Lemurs are an island unto themselves

Madagascar’s diverse lemur population can be described by many adjectives: tiny, jumpy, creepy and smelly, to name a few.

The word “primate” typically conjures up a mental image of chimpanzees and gorillas (and even humans if one isn’t feeling too superior to the rest of the animal kingdom). But these animals are relatively recent additions to the order. For a glimpse of what the world might have been in the absence of such new primates, one need only look at lemurs, which evolved from ancient ancestors without the intrusions of monkeys and apes. With their large (and sometimes glowing) eyes, lemurs can look a bit spooky, leading Carl Linnaeus to name them the Latin term “lemures” – meaning ghosts, and not of the friendly variety .

Desert Island
Lemurs exist in the wild in a single location: the island of Madagascar.* The island nation, which presently lies to the east of the southern portion of Africa, was once connected to the African mainland.† About 160 million year ago, Madagascar disconnected from Africa and began its eastward drift. This was fortuitous for lemurs, because once monkeys evolved on the mainland (about 20 million years ago), they quickly out-competed earlier primates, driving them into extinction. Lemurs escaped this fate through their geographical isolation.

Africa and Magascar in their present day configuration. Image Credit: Blatant World

The logistics behind lemurs’ colonization of Madagascar are somewhat hazy. While the land rift that created the island occurred about 160 million years ago, lemurs appear on the fossil record only about 60 million years ago. So far, the least preposterous explanation for how they made their way to the island is via a “rafting” occurrence, in which a handful of early primates got swept out to sea on mats of vegetation and managed to survive long enough to land in their new home. Stop rolling your eyes – given 100 million years it could happen. And, anyway, it’s more plausible than a “land bridge.” Furthermore, with the newly-formed continent still shifting around, by the time monkeys showed up in Africa, Madagascar was prohibitively far to be reached by additional accidental rafting. Newer, smarter primates didn’t have a chance to threaten lemurs until about 2000 years ago, when humans deliberately rafted over in their man-made boats.

Diversifying the Porfolio
However they made their way to Madagascar, once there, lemurs adapted to a multitude of environments, yielding wildly different animals that encompass five different families and over 70 species. Lemurs include our planet’s smallest primates and, until recent extinctions, some of its largest.‡ Some are nocturnal, while others are most active in the daytime. They sport a dazzling array of colors and patterns in their fur. And, while they sometimes dine opportunistically (eating whatever’s around, not unlike humans) their dietary niches also have striking diversity.

A fine toothcomb. Image Credit: Alex Dunkel

As primates, lemurs have five digits on each of their hands and feet, most of which have nails rather than claws. Both hands and feet have thumb-like opposable digits, allowing lemurs to climb trees with great dexterity. However, they lack the ability to grasp branches with their tails.

The second finger bears a special feature called a “toilet claw.” Before you say “Eww!” and declare lemurs uniformly disgusting, let me explain that the word “toilet” here is used in the old-fashioned sense – “pertaining to bathing” – rather than to denote the ceramic bowl one pees into. The toilet claw is a grooming tool, like a hairbrush. Another built-in hair accessory is the lemurs’ toothcomb – a series of six (or in some cases four) lower teeth that look and function, as the name implies, like a comb.

Lemur Sampler
With so many species of these critters running around, telling you about all of them would be impractical. As with ordering a sampler platter at lunch, you won’t necessarily get the most obscure and exotic of offerings in this section, but it should give you enough information to decide if you wish to come back to the restaurant.

Mouse lemur

Image Credit: Frank Vassen

At less than five inches long (not including the tail), mouse lemurs are pretty tiny. New species are still being discovered, so superlatives are subject to change, but the current holder of the smallest mouse lemur – and thus smallest primate – title is Berthe’s mouse lemur (Microcebus berthae). The species is about 2.5 inches long and weighs barely over an ounce. That’s less than a bag of M&M’s. The small bag, of course, not the one you get at the movies.

These mini lemurs are timid and nocturnal, sleeping in the trees during the day and then venturing out after nightfall to find food, which can be a variety of plants and insects. Not surprisingly, they’re difficult to capture and/or observe, and thus their behavior isn’t very well documented.

Sifaka

Image Credit: Neil Strickland

The medium-sized sifakas are diurnal (active in the daytime)§ but, like mouse lemurs, they still spend the majority of their time in the trees. Sifakas are some of the most skilled leapers among lemurs, covering as much as 10 meters (more than 30 feet) in a single jump. They do this using a technique called “vertical clinging and leaping.” In an upright position, they push off from one tree branch and then turn their bodies in midair to face the next one, landing feet first to absorb shock. Landing and leaping can be done so rapidly that the overall effect looks as though it is controlled by invisible puppet strings rather than the animals’ own muscles. Extra long hind legs facilitate these nimble movements. However, on the ground the drawback of such a disparity between front and back limb length is easily apparent. The sifakas’ short arms make it impossible to get around on all fours. Instead they do a distinctly less graceful sideways hopping. Fortunately the awkwardness is infrequent. Traveling via hops is reserved for those areas where tree branches are spaced too far apart to be leaped in a single bound.

Aye-aye

Image Credit: Tom Junek

Admittedly not the most photogenic of the lemurs. There’s good reason the aye-aye didn’t get its own show on Animal Planet. As you might expect with a creature that looks like this, it is nocturnal, dwelling in the rainforest trees on Madagascar’s eastern coast. Adding to the aye-aye’s creepy appearance is a long, bony middle finger used for locating and procuring food. They tap tree branches with this finger and listen for insect larvae that burrow into the wood. Once found, the same sharp digit can be employed to dig the bugs out from their hiding spot. Aye-ayes also poke their fingers into eggs, coconuts and various fruits.

Island dwelling humans didn’t think much of these animals. Some believed aye-ayes to be unlucky and dealt with this harbinger of bad omens by trying to kill it. Today aye-ayes are protected, so if you see one, be nice.

Ring-tailed lemur

Image Credit: Woodlouse

And now for the most well-known, thoroughly-studied, easily-spotted and perhaps most-loved of all lemurs. These iconic, charcoal-eyed, stripey-tailed animals grace zoos and health food store cereal boxes alike. They are diurnal, but have retained a tapetum lucidum – the reflective layer that gives nocturnal creatures that glowing eyes effect. While they are skilled tree jumpers, ring-tailed lemurs spend more time on the ground than most other lemurs. Their diet consists primarily of plants (they’re especially fond of tamarind) but they’re not above eating bugs or whatever else they can find when resources are scarce.

Because ring-tailed lemurs have been so meticulously studied, I can also report about some of their behavioral quirks, like scent-based communication. In addition to scent marking of territory (carried out by both males and females), males of this species also use scent to assert dominance. After coating their tails with secretions from scent glands on their arms, males wave their stench-soaked tails at each other in a battle of stink. Fascinating, isn’t it? I know, you miss the aye-aye. It’s an adorable animal.

* Two species are also found on the nearby Comoro Islands, but they were most likely introduced there by humans.

† Of course, back then this was not the Africa we currently know, but the super-continent Gondwana, which also contained the landmasses that make up present day Antarctica, South America, Australia, the Arabian Peninsula and southern Asia.

‡ With the introduction of humans, things changed on Madagascar, and lemurs, after pretty much having the run of the place since their initial evolution, experienced significant reductions in number. Those species that were the largest in size suffered the greatest impact.

§ In general, larger species of lemur are more likely to be diurnal. The teeny tiny guys only go out at night.