As I'm sure most of you are aware, scientists have recently discovered that elephants have a sixth toe. Some sources quote it as being a 'false toe', does that mean it is a separate digit in itself, or not?

I was also wondering if this affects the classification of elephants as well. We classify hoofed mammals such as horses and sheep as odd and even-toed ungulates, so does the fact that elephants have six as opposed to five digits mean that we may have to reconsider their taxonomy?

Esme, this was quite a difficult story for the media to report, hence the liberal use of analogy. The most telling factor here is that the original paper does not call the structure a toe (you can see the abstract here: http://www.sciencemag.org/content/334/6063/1699)

Having had a look at the original paper, what John Hutchinson's team are reporting is a structure that is mostly cartilage (like your nose) but with some growth of bone associated with it. Thus it is not the same as the other toes. It does not form in the same way during the growth of the animal. However, it is performing the role of a toe. The problem in understanding is that biologists care about both the function of structures and their patterns of gain and loss so the paper refers to small, tendon-anchoring bones, while in general conversation a toe is a toe.

As the structure is not a toe, this doesn't change high-level taxonomy, as elephants are not in the group of mammals (Ungulates) that rely on numbers of digits for classification.

The study also looked at fossils and found that ancient members of this group lacked the structures found in the modern elephants. So there may be some impact on taxonomy at some level.

"Hope is a duty from which palaeontologists are exempt."
David Quammen

Alistair wrote: "As the structure is not a toe, this doesn't change high-level taxonomy, as elephants are not in the group of mammals (Ungulates) that rely on numbers of digits for classification."

That is true; but even if the number of toes (in the strict sense of the word) did change, that would not change the classification of the elephant. For one thing, although it belongs to the group Afrotheria rather than the group Laurasiatheria that contains the even-toed and odd-toes ungulates (artodactyls and perissodactyls respectively).

But even more importantly, diagnosis is definition. What I mean is that we may use the existence of an even number of toes to diagnose an animal -- a cow, say -- as an artiodactyl; but that is not the definition of an artiodactyl. Groups are defined evolutionarily, by common descent, which is why for example whales (which have no toes at all) are still considered artodactyls. Similarly if a group of cows evolved an extra toe, so that they had an odd number, that would not make them "odd-toed ungulates" (i.e. perissodactyls); they would still be perfectly good artiodactyls.