That's not entirely surprising, given that enamel and dentine are harder than bone, and quite a few animals shed worn teeth all through their life anyway, but nonetheless zoologists and palaeontologists find teeth enormously important in their work. Not only can a good set of teeth tell you what the original owner ate, and even how it moved it's jaws, but the 'teeth formula' is so diagnostic that you can hand a jawbone to a good mammalogist and he can not only tell you what species of New Guinea rodent it used to belong too, but how old it was when it died. Similar tricks are possible with human jaws, too, as populations moved and spread around taking their own variations on incisor shape, molar grooves, and extra cusps with them.
Teeth have been around a long time - although back in the Cambrian they were more used as body armour and scales (sharks still do...) then mere useful decoration for your jaws - after all, quite a few fish back then didn't have jaws to be so adorned. But until mammals came along and invented the teeth formula of incisors, canines, premolar and molar, and milk teeth followed by adult teeth, things didn't really get really specialised. Mammalian teeth arrangements are highly efficient, although problems do arise during the switch from milk to adult teeth, and you're rooted once your adult teeth wear out. In humans, doubly so, since the 'wisdom teeth' many people have as an emergency reserve now cause more problems than they're worth.
Teeth are a defining character for quite a few groups of animals - rodents, for example, discovered the usefulness of incisors that never stop growing, and have never looked back since. A large number of species are known only from their teeth. And a huge number were named after the distinguishing features of their teeth. Kollikodon, the 'Hotcrossbunodon', for example. Or the also extinct order of multituberculate mammals, who indeed had teeth with multiple tubercles. And then there's the Mastodon - 'Nipple Tooth', the Thelodonti - 'Nipple Tooth', and the Bubidon - 'Nipple Tooth' (alright, I made the last one up)
Of course, identifying a new specie's relatives based on one tooth can lead you slightly astray, when the specimen is the first of a kind of vertebrate never before seen by science. Iguanadon, for example, was not particularly iguana-like, but at least some guys got to have a dinner party inside the reconstruction anyway. The three-metre-tall model commissioned by the Australian Museum after Palorchestes was identified by British anatomist Richard Owen as the world's biggest kangaroo didn't even get that ( Owen, incidentally, was also responsible for the Iguanadon cock-up ). Instead, the giant kangaroo got dragged out behind the Museum and bashed to pieces, to spare the museum the embarrassment.
Jawbones can make you look like an ass, in other ways, too - for a long time it was believed marsupials survived in Australia because the 'superior' placental mammals never made it here until very recently. Then two placental jaws showed up, so old they implied that placentals were not only out-competed by the marsupials, but that they may well have evolved here in the first place! The human tooth that showed up in the amazing Riversleigh deposits of Queensland would have turned human evolution on it's head, if one of the palaeontologists hadn't admitted they'd planted it as a joke (and was presumably beaten senseless by their colleagues).
But then you get teeth so weird the palaeontologists can only look at each other and throw up their hands in despair, incapable of even telling what the creature ate. Such is the case with 'Thingodonta'
'Thingodonta' is known from a good number of teeth and jawbones, and one partial skull, again from Riversleigh. It's since been given an official name - Yalkaparidon ' Boomerang Tooth' - and enjoys the distinctive molars of marsupial moles, the ever-growing incisors of rodents but which are also very diprotodontid-like, and the primitive skull of certain bandicoots. But it doesn't seem to be related to any of them. They're so odd they get their own order of mammals - the only order of Australian mammals that's actually gone extinct ( yet... give us a few more years of feral cats etc and that may change). Guesses as to what it could have eaten, given the combination of heavy-duty cutting incisors, and molars too soft to chew with, include worms, caterpillars, or eggs. But these are at best speculation... we simply don't know.
Tune in next time for the animal that scattered teeth all over the ocean, and then remained a mystery for the next 200 million years...