Monday, July 5, 2010

A Diverse Family: Lemurs Part II

In the last post we went over what defines a lemur as their early evolution prior to reaching Madagascar. Now I'm going to cover their diversification after they reached the island.

As I said before the aye-aye lineage broke off from the lemur family tree first, pretty much as soon as they colonized Madagascar. Now, lemur evolution and cladistics (the study of how organisms relate to each other based on evolution) are somewhat debated. I'm going to try to use the most accepted theories to help explain here, but there are always some experts who will disagree.

Extinct members of the aye-aye family are very few and very fragmentary, but one in particular has gained some attention. It is known as the giant aye-aye, and I'll be damned if this aye-aye wasn't giant. The modern aye-aye usually weighs about 3 kg (6.6 lbs) while the giant aye-aye (Daubentonia robusta) was 9 kg (18.2 lbs). That thing would be effing scary! Very little is known about this creepy motha-effer but it likely lived much like its modern relative.

After the aye-aye, the first lemurs to diverge were the ones that most consider the "true lemurs". Ring-tailed lemurs are the classic example of these guys, but they also include critters like the ruffed lemurs, the bamboo lemurs as well as the various kinds of brown lemurs. One particularly large genus of these lemurs existed until about 1200 AD which was called Pachylemur which is also called the giant ruffed lemur. The two species in this genus were about 3 times larger than the average ruffed lemur at about 13 kg (29 lbs) and likely had very similar diets, feeding on flowers, fruit and leaves. For many years it was thought these lemurs were ground-livers (terrestrial) that were easily hunted by the first people of Madagascar, however, recent studies have shown Pachylemur were likely tree-livers (arboreal) like its modern relatives.

Although Pachylemur were quite large by lemur standards there was a completely extinct sister family to the true lemurs called the "koala lemurs" which have some of the largest lemurs ever. They are called as such because they have short limbs and bodies that greatly resemble koalas. The only genus in this family is Megaladapis, which contains three species, the largest of which, Megaladapis edwardsi, was about 1.5 m (5 ft) long and 50 kilos (110 lbs) in weight. Much like a koala, its limbs were well developed for vertical climbing, and likely would have been a very chill animal. It also had an incredibly thick skull with powerful teeth and incredibly powerful jaws that it would have used to mush up any plants within reach. Megaladapis also had a rather strangely built nasal cavity which actually looked somewhat like a rhino. This confused scientists at first but now most believe that it had a prehensile lip, much like some kinds of rhinoceros. This would have helped it grasp plants without letting go of a tree trunk. Another interesting fact about these big guys is that they were once grouped within the sportive lemur family. This was mostly because they have rather similar teeth. However, genetic evidence (which tends to trump pretty much all other evidence) puts them closer to the true lemurs.

Speaking of sportive lemurs, they were among the next two groups that split from the main lemur tree, along with the mouse and dwarf lemurs. Fossils of these critters are rare, mostly because they are so damn tiny and fossils of tiny animals do not tend to fossilize. The modern representatives of this group are all nocturnal and likely look very similar to the ancestral lemurs that first reached Madagascar. They include the tiniest primates in the world, Madame Berthe's mouse lemur, which averages at 30 g (1.1 oz), as well as some of the most recently discovered.

The next group is typically called the "monkey lemurs", and this is because they had habits that were rather similar to modern baboons and macaques (thus I usually call them baboon lemurs to make it more specific). These lemurs were generally large (about 35 kg) and mostly ground living, making them very similar to baboons. The most specialized species was Hadropithecus stenognathus which had an incredibly shortened skull that made it seem almost ape-like in its facial appearance. Its body was compact and its legs were short and stocky, clear signs of a terrestrial (ground living) animal. The shortened skull and grinding teeth were well adapted for grazing on grass, a diet that is rare among primates and is best known in the gelada baboon of Ethiopia. Hadropithecus would likely have been seen shuffling around the hills of central Madagascar plucking grass with its dexterous hands and munching the plants to a pulp. This species group is probably the least studied of all the fossil lemurs, and much more research is likely to be done in the future.

The final groups that diverged were the extinct sloth lemurs and the modern sifakas. Sloth lemurs are so named for their likely habit of hanging from branches like a modern sloth. They had highly flexible hips and shoulders that allowed for some rather interesting ways of hanging whether it be upside down or from one limb, sloth lemurs could do it all. The largest of these species was Archaeoindris fontoynonti which weighed about as much as a modern gorilla; 200 kg (440 lbs). Unlike gorillas, Archaeoindris likely spent almost all of its time in the trees and moved much like an orangutan, swinging slowly from branch to branch in search of fruits and leaves.

The final group we are going to talk about is my personal favourite family of lemurs, the sifakas (pronounced shif-ahk) and their relatives. These guys are known for their rather classic lemur appearance, but unlike true lemurs, they travel on two-legs when on the ground by hopping somewhat comically. From what I've gathered no extinct species of these cool leapers have been found, but they are closely related to the gigantic sloth lemurs.

So, what exactly caused all of these lemurs to go extinct. Every extinct species I have mentioned was gone from the Earth in the last 2000 years. This is comparatively recently when you think about other large mammal extinctions (eg. the sabretoothed cats) so from the very beginning man kind was thought to have been the cause and it sis very likely over-hunting was the main culprit in their demise. In fact, almost all large animals of Madagascar went extinct almost as soon as man arrived, including elephant birds, giant fossas and dwarf hippos.

So that is all on lemurs for the next little while. Hope you weren't bored to death by all of this but I also hope you learned something. =P Next we'll take a closer look at each extant (living) lemur group.

Oh, and BTW, I think I've decided to make Gordon the Proto-Aye-Aye the mascot of my blog, so you'll probably be seeing lots of him. XD

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