Natural History

Mozilla Firefox is a browser with an interesting zoological name.

I think it’s a little strange that people don’t know what a “firefox” is, but it is an alternate name for the red panda. The company that developed the browser is quite into red pandas for this reason, but I don’t think the typical user of the product really thinks much about the name.

Red pandas are perhaps the most unusual carnivoran from a taxonomy perspective.  For most of the twentieth century, it was assumed that red and giant were close relatives. Both animals live in Asia, and both have this unusual “thumb” that is made out of one their wrist bones. The feature is used to grip bamboo, and it was just assumed they evolved this trait from a common ancestor.

Red pandas look a lot like raccoons, and it was proposed that they were procyonids, just because they looks so much like a more specialized form of raccoon. And if this animal is a raccoon and the giant panda is its closest relative, giant pandas are not bears.

The classification of the giant panda was resolved though a molecular and genetic measures that were published in 1985. Giant pandas are bears, though they are a very divergent form of bear. Further, the giant panda’s chromosomes were found to be mostly fusions of the typical bear karyotype.

Red pandas, though, were even more strange. They weren’t bears, and they weren’t procyonids either.  In this study, they were as divergent from bears and procyonids as bears and procyonids are from each other, but the techniques in those days were rudimentary and not conclusive.

However, this finding suggested that red pandas really are something else. They were given their own family name (Ailuridae), and researchers have spent several decades trying to figure out where these animals fit in the order Carnivora.

Of course, figuring out exactly where they fit they were took some time. In 2009, we finally got a good molecular study that looked at a relatively large same of nuclear DNA of red pandas, procyonids, mustelids (weasels, ferrets, otters, wolverines, martens, and mink), and mephitids (skunks and stink badgers).  It found that red pandas formed a clade with procyonids and mustelids. They are roughly as closely related to mustelids as they are to procyonids, so they definitely do deserve their own family name.

This is largely the consensus view on where red pandas fit, but there is an alternate view that has popped up as result of another molecular study.

In 2010, an analysis of the cytochrome-b sequences from 243 carnivoran species and subspecies found something unusual. The red panda was found to be most closely related to canids.

This finding is somewhat surprising, and because this study is based upon a very small part of the mitochondrial DNA from each sample, it is problematic. If you look at the phylogeny proposed in this paper, it puts the kinkajou outside of Procyonidae, and a clade is formed with the Ethiopian wolf, red wolf, and the coyote, while another clade is formed with the various subspecies of the Holarctic wolf and the golden jackal. These are problematic because full-genome comparisons tend to place the coyote as much closer to the Holarctic wolf than we ever thought, and the exact position of the other species still must be worked out.

But let’s just say that this study’s findings about the red panda are later confirmed in another nuclear DNA study or one that uses full-genome comparisons.

If the red panda is the closest living relative to the dog family, then we’ve got something interesting. Canids were an early diverging family in the order Carnivora. Their sister family were the amphicyonids, which are often called “bear-dogs” in English. This family consisted of plantigrade species that were sort like wolverine-lions. They went extinct 1.8 million years ago.

Dogs are not that closely related to rest of what are called the “caniform” carnivorans, so when the amphicyonids became extinct, they were the last of their lineage.

If the red panda really is that close to the dog family, its exact position with regard to both canids and amphycyonids is not entirely clear.  It could be that red pandas are actually a sister taxa to the extinct bear dogs, which would be an interesting find.

One should keep in mind that the red panda family used to include some pretty fell beasts.  Simocyon was a genus of cougar-sized predators that lived throughout Eurasia and was also found in North America and Africa during the late Miocene and Pliocene epochs. These creatures were fully carnivorous– and they had the wrist thumb that one finds on the red panda living today. The discovery of this thumb on this extinct relative with such a different ecological niche revealed that the red panda’s thumb came about far earlier than we expected. And it had nothing to do with gripping bamboo to eat.  It had more to do with climbing around in trees.

The giant panda’s thumb does have to do with eating vegetation.  A Miocene bear in the panda lineage from Spain called Indarctos arctoides already started to have some deviations with the bone that becomes the “thumb” in modern pandas.

The trait evolved without any common ancestry, and it is only one of those ironies of natural history that these two creatures have this feature and use it in much the same way.

So giant panda really is a bear, and the firefox might be a kin to the dogs.  (But probably isn’t).