Closest living relative of the primates...
Above is a photo of a unique member of the mammal clan, the flying lemur or colugo (Cynocephalus volans) from the collection at the Cincinnati Museum Center. This specimen was collected by former CMC zoology curator Robert Kennedy in 1987 on the Philippine island province of Biliran, the first record of this species for that location. This is the skin of the specimen. The skull and most of the skeleton are in the collection of the Smithsonian Institution. The fur is amazingly soft, a little like rabbit fur, and the digits have big recurved claws that look like those of a cat.
Flying lemurs aren't lemurs at all rather they belong to their own unique mammalian order; the dermoptera. There are only two species of flying lemur in the world and both are found in the tropical forests of South-East Asia. One species, the Sunda Flying Lemur (Galeopterus variegatus), is found on the Indo-Malay Peninsula, Singapore, Sumatra, Java and Borneo while the only other living flying lemur, the Philippine flying lemur (Cynocephalus volans) is confined to the islands of the Philippines. If the lemur misnomer wasn't confusing enough, flying lemurs don't fly either, at least not powered flight like a bird, butterfly or bat. These arboreal mammals can glide from tree to tree much in the same way a flying squirrel does. The limbs are connected by loose folds of skin and when the limbs are outstretched the skin creates a large surface area that provides lift in the same way the stretched out fabric of a kite keeps it aloft. Flying lemurs are mostly active at night and they are herbivorous with their diet consisting mainly of leaves, fruits and flowers.
For a long time the place flying lemurs occupy on the mammal family tree has been a mystery. Most scientists placed them somewhere in between insectivorous mammals, like shrews and moles, and the bats. However, a recent study published in the journal Science by Jan Janecka (Department of Veterinary Integrative Biosciences, Texas A&M University) and his colleagues uses modern comparative genomics to shed light on the evolutionary relationships of flying lemurs. As it turns out, according to Janecka and colleagues, the common name flying lemur is not as far off as once thought. The two extant species of flying lemur are the sister group to all the primates, that is to say that primates as a group and flying lemurs are each others closest relatives. This conclusion was drawn on the basis of DNA sequencing of nearly 14,000 letters in the genetic code from flying lemurs, primates, treeshrews and other mammals. Analysis of these DNA sequences reveal that there are shared genetic mutations in flying lemurs and primates that are not found in other mammalian groups. For example, for a particular gene called TEX2 flying lemurs and all the primates sequenced in this study share a deletion of three amino acids not found in other mammals. Together the combined results from these genetic data suggest that the evolutionary split between primates and flying lemurs occurred approximately 63 million years ago, shortly after the extinction of the dinosaurs.
Does this mean that gliding flight was a trait in the ancestors of the primates? Probably not. It is important to remember that flying lemurs have undergone as much evolution as primates since both split from a common ancestor about 63 million years ago. The specialized characters found in modern flying lemurs evolved over time. Because the closest living mammalian group to the grouping of flying lemurs and primates are the treeshrews, a group who (like primates) do not exhibit the gliding behavior found in flying lemurs, one may conclude that the specialized gliding lifestyle of flying lemurs evolved after their split from the mammalian lineage leading to modern primates.
The Janecka study, and many others like it, emphasizes the power of modern molecular genetics in untangling evolutionary puzzles. Because of their close relationship to the primates flying lemurs have the potential to tell us much about the early evolution of primate genomes, including the human genome.