I heard a conversation recently in which someone said that her dentist mentioned that human “canine” teeth are not “true canine” teeth. Now, in common parlance there are a number of critters with names that aren’t indicative of their taxonomy or phylogeny (eg., horshoe crabs, musk oxen, electric eels), but were named possibly before that information was well-known.
However, I understand what the “true crabs,” “true oxen” (well, I’ve never heard that term, but I understand what it would mean), “true eels,” etc. mean, and how biologists can classify them, but what about “true canine” teeth?
I’m assuming it doesn’t mean the literal meaning of “canine.” Does it mean that only “true carnivores” or at least carnivorous animals have canine teeth? I didn’t find much information on the definition of “true canine” teeth.
Well, they are not, strictly, “single-rooted conical-shaped teeth coming to a sharp or blunt point which fall approximately at the two apices of the jaw curve, lying posterior to the incisors and anterior to the premolars along that curve” since in us the upper incisors come to more of a blade. And they are clearly not in the mouth of a canine. But these two nitpicks aside, they are precisely homologous to, and evolutionarily descended from, classically shaped canine teeth.
So when is your dentist signing up for the SDMB? Sounds like we could use him.
Well, there are two senses of “canine teeth.” One refers to their anatomical origin, another to their function. Human canines have the same developmental origin and position as the canine teeth of carnivores, so that’s why they are referred to as such. However, they are not as large, pointed, or sharp as those of carnivores, or even those of other primates, so in that sense they do not really function as canines. But to an anatomist, human canines are certainly “true canines.” Your friend’s dentist is making a distinction that would not really be made by a mammalogist.
This sort of modification of the function of teeth is common in mammals. For example, the tusks of boars are canines, but they do not really function as such, not being used in the capture of prey. Shrews and many other insectivores have sharply pointed incisors used in capturing prey that function as canines. Which of these are “true canines” and which are “false” depends on whether you are looking at it from an anatomical or functional perspective. But most mammalogists would probably take the former view.
I think you meant to say “canines” in the last part of that sentence. That would go for both upper and lower canines.
