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All the better to eat you with...

The diet of an organism is one of the most fundamental aspects of its ecology.  The search for and processing of food drives evolution of adaptations in behavior, morphology, and physiology.  So it's no wonder that figuring out the diets of extinct organisms is one of the common goals in paleontology.  And teeth, in those organisms that have them, can give us a window into an organisms diet.
Since chewing or biting is the first stage in the processing of food, the shape of teeth relate to the sort of physical processing that goes on.  This should make intuitive sense - when you see an animal with big sharp teeth with long blades, you probably would guess that it's a meat eater.  If an animal had flat teeth with grinding surfaces you would think it ate plant matter of some sort.
Mammalian Dentitions
Paleontologists do this too, although at a much finer scale.  The key to it all is the phrase that drives much of paleobiology - "The present is the key to the past".  I've mentioned this a bit in relation to teeth in a previous post, but this time I'll talk about food processing in a little more detail.  The key is that by studying the teeth of modern animals, for whom we know diets, we can make inferences about the diets of extinct animals by comparing their teeth to those of living taxa.
This sort of inference was shown recently in a study on a new early bird from China.  This new bird taxon, Sulcavis geeorum, has blunt, rounded teeth, similar to modern animals which eat hard-objects.  A good modern example would be otters, which use their teeth to crush clams and urchins.  In addition, the enamel on the bird's teeth (the hard outer covering that gives teeth their strength) is grooved.  Grooved and crenulated enamel has been found in other taxa, and has also been associated with a diet of hard objects.
Sulcavis geeorum reconstruction
Many early birds had smaller teeth, adapted for eating insects or possibly fish.  Of course modern birds don't have any teeth.  Instead they have other adaptations for processing food.  Beaks work well for obtaining food, from needly beaks of warblers used for catching insects to the sturdy beaks of parrots and toucans used for getting into fruits and nuts.  The evolution of the beak in birds is probably linked to the loss of teeth and this evolution has occurred a number of times.
Some birds also have a gizzard.  This is a muscular segment of their gut with grit and sand inside.  Birds swallow food and it is transported to the gizzard, where the organ's muscular walls crush the food and grit, helping the physical breakdown of the food.  Some dinosaurs probably had a similar organ.  How do we know?  Smooth stones, called gastroliths ('stomach stones') have been found in association with dinosaurs, especially sauropods, and are thought to be from a gizzard.  They can be distinguished from other stones by their characteristic wear, which can't be made by other natural processes, and their location relative to skeletal remains.  (Some marine reptiles may have also used gastroliths for buoyancy control, but that's a story for another time...)
Gastroliths in a ceratopsian
But back to teeth, the study of the teeth of Sulcavis demonstrates one of the great points of evolution - that of 'convergence'.  Animals that do similar things tend to have similar adaptations.  They may have come at them independently, and in different ways, but their function has helped lead them to have analogous shapes.  The fact that we see this pattern again and again in across evolutionary history speaks to the power of natural selection - environments shaping the morphology of organisms.  So it's only appropriate that we talk about this now, during the week that would have been Charles Darwin's 204th birthday.  His discovery of the mechanism of evolution - natural selection - allowed us to explain these patterns that we had been seeing for some time, and we continue to use the same principles today as biologists broadly, and paleontologists specifically.
Posted: 2/17/2013 12:39:12 PM by oldbones | with 0 comments

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