One idea that has developed since Darwin that contributes to our understanding of evolution is continental drift. South America rather like pre-human contact Australia was a floating Ark of diverse and wonderful marsupials - then it hit North America!

Today only the opossums remain of those marsupials, South America is now a placental mammal kingdom, with a large range of Carnivora. So what happened? Well the obvious answer is that the placental mammals were fitter, but what you need to bear in mind is that rather than mutations happening in-situ and some proving to be an improvement à la Darwin, the process is now much more dynamic. Continents collide, animals that had evolved in isolation now meet, and in the process of the continents colliding the ocean currents shift and as a result the whole world's weather is altered. It then becomes, not which animals are better suited to the environment they evolved in but which can better survive and adapt to the changing conditions.

The winners that result from this very dynamic process are usually the more adaptable. It follows that highly specialized animals are an evolutionary luxury that can only develop in settled times, times of continental collision or climate change are likely to be a death sentence for the specialized.

The likely conclusion then is that the placental mammals were generally more adaptable than the marsupials.


Adaptability has also been suggested as part of the difference in the Carnivora and Creodonta competition. This comes down to the teeth.

Teeth are very important to paleontology because they survive. Teeth, the jaw bones and skull that they are associated with are very durable and show significant differences between species and between genera. (Genera are groups of related species, genera are then grouped into families, families into orders, and so on. Where only a few fossils survive identification of species is very difficult, a species will only tend to last for a million years before being supplanted, and so paleontologists who deal with much more sweeping timescales than that tend to talk about genera). The result of the survival of teeth is that identification of fossils often comes down to the teeth. Read a paleontological book and pages and pages can be devoted to the skull and teeth where the post-cranial skeleton (everything else) is lucky to get a paragraph.

a carnivore's teeth - click for source site

An illustrative picture of some of a typical carnivore's teeth (the nose would be top right)

creodonot skulls - click for source site

The skulls of two different creodonts

Compare the pictures above, get a feel for the differences between the teeth types and you are behaving like a paleontologist! You can tell straight away that all three animals are flesh eaters. It's not just the big front teeth on the creodonts that gives it away but the fact that the rear teeth look like they have been designed for cutting not grinding as you would expect from a herbivore or pointed for gripping while swallowing whole like those of an insectivore. In fact the top picture has arrows to indicate the cutting action of the very specialised carnassial teeth of members of the Carnivora order. If you own a cat or a dog you have perhaps seen them turn their head to one side when eating to bring this cutting action into play.

The creodonts have a very similar structure but the key difference lies in the fact that their cutting teeth are their back teeth. The carnivora by contrast have another pair top and bottom behind the carnassials. Now I don't know that anyone is convinced that this is the decisive difference but I have seen it suggested that the fact that carnivores have a more generalised tooth behind their meat shearers allows them to adapt to a less than wholly meat diet in times of hardship. The difference in adaptability is slight but over the course of twenty million years it doesn't take much of a difference to add up to the one order being extinct and the other having been at the top of the evolutionary arms race until the bow and arrow came along.

Staying on the subject of teeth - consider the walrus:

A truely strange animal, a pinneped along with seals and sea-lions and as such a member of the Carnivora order. But something further away from our idea of a classic carnivore like a cat is hard to imagine. Even the completely vegetarian Giant Panda seems to better belong to the Order than this animal of sea and ice that uses its fleshy lips to suck out the contents of the shell fish it feels for on the ocean bottom. The Walrus's tusks are used to scrape around on the sea bed, to help purchase on the ice and occasionally to joust with for territory - hardly sabre toothed.. and yet consider these two images
Two skulls mounted for sale, on the left the walrus and on the right one of the sabre toothed cats Hoplophoneous. Ignore the disproportionate sizes and look at the shape of the tusks verses the sabres, if you don't see what I mean try another image of walrus tusks...

Note the shape and particularly the grooves down the tusks and spot that the same grooves are on the cat's teeth. The same grooves are found on our own metal daggers to increase the dagger's strength to weight ratio and to allow the suction created when the dagger is being pulled out of wet flesh to be released.

That the teeth of sabre toothed cats should resemble our own killing implements only seems to reinforce the argument that these animals were the most formidable predators. But why should the same form be found on the teeth of a mollusc eater?

Finally on the similarities between the sabre toothed cats and walruses, much is made of the jaw morphology of these cats in that the lower jaw seems to have been able to swing open a very long way. There are palaeontologists who have matched the jaw and teeth spacing of various sabre toothed jaws to the necks of individual prey animals. And yet a glance at the walrus skull seems to suggest that a walrus's lower jaw can also swing open beyond 90 degrees - why?

So what am I saying here?

Well in truth I'm not sure. Certainly noting the similarities between a walrus's tusk and a sabre toothed tiger's sabre gets me no nearer to answering the original question about sabre toothism i.e. why would such delicate teeth that were probably an encumbrance to hunting develop separately at least four times in three orders of mammals?

And certainly I can see the logic behind connecting predator tooth shapes to prey neck shapes, indeed such specialisation neatly explains the demise of the sabre toothed cats in a time of global warming at the end of the last ice age (see above).
But I look at the pictures of walrus skulls on the web and I doubt the belief that the sabre toothed carnivores are extinct!!

 In my maddest moments I think that sabre toothism did not arise twice in the Carnivora Order but three times.

That one of those sabre toothed animals lives in the Arctic today and eats molluscs.

And that since this animal does not prey on large animals sabre toothism can not be a function of hunting!!!!!