Hi!

I've read that scientists use the size and shape of teeth to determine what an animal ate. And so you could find out whether a certain dinosaur was a herbivore or ate meat. But what if the environment changed so quickly that the evolution shaping the teeth to suit the food source lags behind?

For example, what if there was an ape with big molars and canines for eating meat but their prey suddenly went extinct? What if they had to switch from meat to mostly fruit? And what if this change happened in a few thousand years so that the teeth doesn't have enough time to change?

Won't scientists get the wrong idea about what this ape was eating? How do scientists figure this sort of thing out?

Thank you.

Hi Joon,

A good question.  It is not only the shape and size of teeth that is used to say what an animal ate, although simplistically, if an animal has broad flat teeth , or thin pointed teeth, it is likely that the animals ate plants or meat, respectively.  However, it is possible to look at an animals teeth in such detail, using techniques such as Scaning Electron Microscopy to see the microwear on the teeth.  These tiny marks, scratches, and scrapes, on the surface of the teeth, can tell us what sort of foods the animal was eating, and how the teeth occluded (came together and moved over each other).  You can look at fossil herbivore teeth and tell what the vegetaion was like.  If teeth are relatively highly worn down, in a young animal you can tell that the plants were tough, and the microwear may suggest that the plants making up the diet contained things like 'silica' (sand like crystals)  to help make the plant unpalatable.  The marks that we see in fossil teeth can be compared with that which we see in living animals, and we can build up a clear picture.

So to your question about apes.  Ape and monkey teeth are interesting.  If you look at them in isolation you will possibly make mistakes about what is eaten.  If you look only at the canine teeth of a gorilla, you would think that this creature must be a meat eater.  The canines are huge, but in context of the jaw you see that they are part of the dentition (the entire set of teeth) of an animal that is an omnivore (one that has both meat and plants in its diet).  In fact the majority of the gorilla's diet is fruit.  Chimps are a little different.  They actively hunt, and often eat monkeys.  Again they have large canines, but they have other teeth that do very well eating fruit and plant matter.

It is fairly true to say that if an animal is an obligate carnivore, that is it can only eat meat, like a lion, then the chance of it surviving if all the prey animals it eats go extinct is low.  It will not be able to survive on a new diet of grass and vegetation.  This is not just because the teeth cannot strip the leaves from a tree, or adequately chew grass, but because the physiology of a carnivore will not be able to get sufficient nutrition out of vegetables.  The result is, it will likely go extinct with its prey.  This occasionally happens in local populations of carnivores when their prey dies out in one area, and they cannot find a suitable alternative to eat.

So, in answer to your question the dentition that is seen in a fossil is a very good indication of what it ate, and taking the type of teeth seen in modern animals, with knowledge of physiology we can make very good analyses of the type of teeth and the diet of animals that are now extinct.

Hi Joon. To add to Neil's answer, you have hit upon a more general issue in evolution - if an animal is adapted to a particular way of life (lets go with your example of diet) and conditions change (in your example this would be food supply) then what happens next? Well, there are three possibilities.

By far the most likely thing that will happen is that the animal simply moves to a place where conditions are 'normal' for its way of life. This is easily observed in nature with animals like butterflies and grizzly bears now moving North with the onset of global warming. These animals are literally 'tracking' the environment, including the kinds of foods they prefer, as it shifts about the earth's surface. However, what if this isn't possible (e.g. the food you are adapted to eat has disappeared altogether)? There are two options left: extinction or evolution.

Extinction is more likely if the animal in question is a 'specialist' or if the change in conditions is particularly severe. A good example of a dietary specialist is the Panda, which will only eat one kind of grass (bamboo). If bamboo was to disappear then it would most likely be curtains for the Panda (it simply isn't built to eat anything else). Alternatively if a change in conditions was particularly severe and occurred quite quickly then it would most likely cause an awful lot of extinctions, with many different types of animal disappearing at once. Such events are recorded in the fossil record as 'mass extinctions' - the most famous of which deposed the dinosaurs (at least the non-flying kind) some 65 million years ago.

So what of the third result? You might be suprised to know that evolution (a change of lifestyle) is the least likely outcome of all. However, an important point to get across here is that the teeth, and indeed almost any other feature of an animal, exists because of evolution - because they enable an animal to do whatever it does. In other words you can't be a meat eater and have the teeth of a herbivore - they simply wouldn't do the job. We can be quite confident about this because we never see (e.g.) a pack of sheep munching on a freshly killed wildebeest. Not only would their teeth be unsuitable for the job of tearing flesh and crunching bone they simply wouldn't be able to run around chasing and catching another animal. Think about all the features that make a top carnivore like a lion so good at its job: sharp teeth and claws, forward-facing eyes for judging distances, strong powerful muscles for running and catching another animal. It works the other way too. Cows don't just have teeth suited to munching on grass, they also have three extra stomachs to help them digest it!

For a major evolutionary transition to occur (e.g. switching from meat-eating to plant-eating) there has to be a plausible intermediate. Lets go back to our poor old Panda. He eats grass (bamboo), but his nearest relatives (other bears) will indulge in both meat and plants. It seems likely that the Panda simply lost the meat-eating part of his diet (and the adaptations necessary to do so) as he found a place where one type of food was in abundant and constant supply. All animals will go for an easy life given the option, and an on tap, year round supply of bamboo has turned the Panda into the evolutionary equivalent of a couch potato. Meanwhile the poor old Grizzly bear has to be a less fussy eater as he lives in an environment where sources of food are always variable. Sometimes there are nice juicy salmon, other times the menu consists of roots, insects, nuts and berries. Grizzlies have even learnt to hibernate to cope with the long North American winters when there is so little food available its simply not worth the effort of running about looking for it.

I have waffled on for a bit, but the thing to keep in mind is that ALL animals are adapted to their environment and way of life - they have to be to exist!

Last edited by Graeme Lloyd (4th Mar 2007 21:56:30)