Monday, February 11, 2013


We have all heard the stories of paleoanthropologists digging up a single tooth and working out from it that it belongs to a new species of early-human, and saying something about its diet and behavior and taxonomic relationships and deriving a natural history for it. I myself love creating complex theories out of minimal evidence and feel I missed my calling by becoming an English teacher instead of a paleontologist (Cheryl thinks I did the next closest thing by becoming a fiction writer).

I might very well have gone the other way. As a kid I loved skulls and began building up a collection of them that I'm still adding to, and which is sitting on an entire bookcase shelf just across the room from me as I am writing this. I used to (well, I'm still doing it) keep an eye out for roadkills that weren't too badly smashed up, and if I found some animal whose skull I particularly wanted, I would set it on the shoulder off the road, somewhere out of sight from others (who might steal it from me?), but where I could find it again, and then I would come looking for it several months later. You try to gauge just how long to leave it, to some period where the bugs have mostly cleaned it up, but it hasn't totally disintegrated. But if it was an especially choice animal I would cut the head off right then and bring it straight home and put it in a jar or bucket of water and stick it in the farthest away corner of the yard to let it "macerate." The far corner because it wasn't pleasant to see, and it could really stink. And it took forever, months and months. If you timed it just right, when you poured all the stinky goop out on the ground, the purest whitest most beautiful skull suddenly appeared out of it, which a gentle hosing (trying to be careful no loose teeth were lost) and drying would make into a perfect specimen. If you waited too long every separate bone would fall apart and you would be left with a 1000-piece 3-D puzzle to glue back together.

Skulls are beautiful intricate sculptural objects, and, fair play to the paleontologists, you can learn practically everything about an animal from its skull, especially from its teeth. The reason I am going on about them here is that my son Gawain and his friend Heather saw a book they knew I would like and got it for me as a Christmas present. The book is called "Skulls," and is by Simon Winchester ("The Professor and the Madman," "Krakatoa," etc.), and is about Alan Dudley, who was like me as a kid but raised up a few levels of magnitude, and now has the largest personal collection of skulls in the world. The text says something about Dudley's obsession and so on, but the text is very brief, and mainly the book is page after page of photographs (by Nick Mann) of the skulls themselves, and (at least for an old collector like me) they are wonderful. They have made me look again at my own I admit rather dust-covered collection, and I am pleased to notice that, on its tinier scale I have also tried to create a representative group of different types, particularly of mammals.

What I'm going to do here is to show (well, show off) a few of my own skulls and point out some of the ways the teeth indicate diet and even behavior.

Here for example is an Eastern Mole. It's an insectivore, and this is  indicated by its undifferentiated teeth. They are virtually all just the same, simple pegs, which are ideal for picking up an insect or worm, and perhaps ripping it into chunks small enough to swallow without much chewing,

People sometimes ask me if moles are related to mice and rats, because they are similarly small furry animals that live in the ground. But look here at this skull of a Brown Rat. It has highly differentiated teeth. It has two enormous incisors in the front, designed for digging burrows in the ground, or biting off thick plant stocks. It is an omnivore that is fond of eating meat, but there would be no room for canines behind those incisors, so it has no canines, and uses the powerful incisors instead as killing weapons. Any food that comes into the mouth goes straight to the back of the mouth to be chewed up by the molars.

Here is another animal totally unrelated to moles, an armadillo. But because it has a similar insectivorous diet, it has evolved a similar mouth full of simple peg teeth. The teeth, in other words, indicate diet, but can be tricky to use to show taxonomic relationship.

Here is another example of this fact. This is a harbor seal. Note in the second picture how the very large brain has been flattened out to the side to keep the profile of the skull flat, unobstructed, and aerodynamic for smooth fast swimming. But note especially that the canine teeth of this carnivore have been somewhat reduced to be more the size of the other teeth, and all of the teeth are tending towards being pointed. Fish are so fast and swerving that it would be difficult to use an accurate bite with canines to capture them. What is needed is a mouthful of sharp points so that any kind of bite can impale the slippery prey and hold on to it.

Now look at this: Here is a river otter, a totally unrelated animal, a kind of aquatic weasel, but also an animal that catches fish by swimming swiftly after them. Note here that, almost identical to the seal, it has a flat aerodynamic shape to the skull, similarly with its quite big brain (does that mean fishermen have to be smart?) squashed out to the sides to keep the top flat, and most similarly its carnivore's teeth have been modified to be sharp fish-snaggers.

Here is the skull of a domestic cat. The cat is a total carnivore; virtually one-hundred percent of its diet is meat. What you see are very long sharp canines with a gap behind them so that they stand clear of other teeth and can be stabbed their full length into their prey. In this case they are especially designed to go around the neck bones of their small prey and quickly break the spine. Then notice how few back teeth they have. There is not a heavy complement of molars, because cats don't do any chewing. Instead the few molars they have are modified into carnassials. The upper and lower teeth fit together like the blades of a scissors and their function is to slice. They cut meat into small pieces and it is then swallowed directly. The second picture, from the front shows another carnivore adaptation. The incisors are practically nonexistent. Incisors are most useful for biting off plant material, something a cat has no use for.

Here is a bobcat skull. Except for the size (which you can't tell from this picture) it is virtually identical to the house cat. Cats are in fact perfectly designed for their stalk-and-leap style of hunting, with forward-facing eyes (the snout shortened so as not to be in the way) for accurate triangulation, the teeth reduced to a functional minimum (it would take a longer snout to fit more of them in). When cats evolved to fit into another niche, it was to hunt a different size-range of prey. They didn't change their perfect design, they just got larger or smaller.

To show what I mean, here is a puma. (This skull unfortunately has the upper canine broken in half, so in the second picture I will show it turned around to show the length of the full canine.) It's a bit more massive, but it's still the exact same design.

Here they all are together.

Here is a carnivore with different behavior, a coyote.  A cat often makes a surprise leap on sitting prey, and can set its canine teeth accurately. A coyote is often chasing swift and elusive prey (rabbits, for instance), and with its long jaws with canines at the tip end, can nip repeatedly until it gets a good hold, and then can bite to make the kill. But also, as the second picture shows, it has much better developed incisors than a cat, because coyotes eat vegetable food as well, melons and fruits, and for that, as the third picture shows, it has a full set of molars for chewing.

There's one more skull I want to show.  This one reminds me of a time I was attending a conference in Washington D.C. and had a few hours off and wandered into the Smithsonian to some rooms full of skeletons and particularly skulls. One room was all primate skulls, from tiny monkey skulls the size of a hen's egg to enormous orangutan and gorilla skulls. No one was around and I was sort of daydreaming as I entered the room, and suddenly I was surrounded by staring faces. After all, we are all primates. These had big craniums, and most had flat faces with two big staring forward-facing eye sockets. I was briefly quite startled. They were all human faces, humans of all different sizes, but what was most unsettling is, they all had big powerful canine teeth. They were monsters, demons, vampires. Several years ago when Gawain came back from a trip to Brazil he brought me a monkey skull, one of my prized possessions. If I hadn't known it was a monkey, if I was just handed the skull and was asked what I could gather about its diet and behavior, I would have guessed that it sneaked into our bedrooms at night and sucked our blood.

1 comment:

  1. Speaking of insectivores, have you seen the latest on the placental mammal split?

    Tl;dr: mathematical analysis of general mammalian genetics suggests that they didn't arise until after the Cretaceaus extinction.