Colugo bumps tree shrew as closest primate relative

Today National Geographic news has an interesting story up today about a recent paper published in Science, apparently a new DNA study has given us new clues about the organism that is ancestral to today's primates. For a long time the tree shrew was cited as being the closest sister taxon to primates, but now genetic evidence suggests that the colugo deserves that distinction instead. (This organism is also known as the "flying lemur," despite the fact that it does not fly and is not a true lemur).

Previous research has shown that the colugo was closely linked to primates, but the new research shows that it could actually bump the shrews for the "closest" position. Although the colugo genome hasn't been completely sequenced yet, the researchers were able to compare some of its genetic data with that of primates and other outgroup species, and determined that the primates shared seven distinctive genetic sequences with the colugos, as opposed to only one shared between primates and tree shrews. They study also confirmed that all three groups are closely linked in evolutionary terms, however, with tree shrews diverging first and then colugos and primates diverging millions of years later.

The molecular data indicates that the colugo-primate divergence happened about 86 million years ago, when dinosaurs were still roaming the earth. This is about 30 million years older than the first known primate fossil, but fossil formation is so incredibly unlikely that just because we don't have a fossil for a given transitional species does not mean that it didn't exist. In paleontology, it is always very important to keep in mind that absence of evidence is not evidence of absence. It is speculated the pen-tailed tree shrew, Ptilocercus lowii, is probably the living mammal that bears the closest resemblance to the common ancestor of all three groups (tree shrews, colugos, primates)

There are two species of colugo living today, Cynocephalus volans and Galeopterus variegatus. Both face very serious threats of being wiped out due to habitat destruction. C. volans, the Philippine Flying Lemur, is classified as threatened by the IUCN, and things are looking grim for G. variegatus as well. Not surprisingly, they are not the only ones in trouble; tree shrews face threats also. Quote from the National Geographic article, forgive the slightly incorrect spelling of P. lowii's common name (if you try to Google it use "pen-tailed" instead of "pentail"):

"We suggest that a global priority be placed on the conservation of the pentail tree shrew and its habitat," Murphy said, "as extinction of this one species would result in the loss of a 63-million-year-old lineage.

Maybe this will spark some new interest in conserving these species. Considering that they are tropical animals, their habitats are brimming with biodiversity and playing the "charismatic megafauna" card could work as an umbrella to protect literally thousands of species that share their ecosystems. I think the implications of the study are extremely intriguing, and if you want to read the original paper the citation is:

Janecka, E., Webb Miller, Thomas H. Pringle, Frank Wiens, Annette Zitzmann, Kristofer M. Helgen, Mark S. Springer, and William J. Murphy. 2007. Molecular and Genomic Data Identify the Closest Living Relative of Primates. Science 2 November 2007 318: 792-794.

At some point I will get around to blogging about the controversy over whether Chiroptera is truly monophyletic, there have been some suggestions that the Megachiropterans are actually more closely related to primates than to Microchiropterans, but that is an in-depth topic that will have to wait for a time when I'm not swamped in coursework (ha, whenever that might be...;p).

(Picture credits to D. Lim and S. Askay)