“In a word, the form of the tooth entails the form of the condyle; the forms of the shoulder blade and the claws, just like the equation of a curve, entail all their properties. Just as in taking each property seperately as the basis for a particular equation, one would find both the ordinary equation and all the other properties of any kind, so likewise the claw, the shoulder blade, the condyle, the femur, and all the other bones taken seperately, determine the teeth, and each other reciprocally. Beginning with each of them in isolation, he who possesses rationally the laws of organic economy would be able to reconstruct the whole animal.” — Cuvier 1812, trans. Martin Rudwick.
Baron Georges Léopold Chrétien Frédéric Dagobert Cuvier was a man of strong opinion and bold statement. In the most dramatic articulation of his “Principle of the Correlation of Parts” Cuvier argued that anatomy, like God, bows to math. Given a single isolated bone, he claimed, one might be able to infer what the entire animal looked like, at least in principle. In following paragraphs Cuvier hedges his bold assertion just a bit, but this is the idea for which Cuvier is remembered, and misremembered, the most.
Creationsists love to bring this up, “scientists find a few scraps of bone and make up a dinosaur.” Ironically, it was Cuvier’s own vision of “intelligent design” and “irreducible complexity” that informed his view. On the opposite side of the spectrum, Thomas Henry Huxley took Cuvier’s claim to task in his lecture “On Natural History, as Knowledge, Discipline, and Power” (see also Hugh Falconer’s rebuttal). In a later, and tremendously entertaining essay, “On the Method of Zadig” Huxley argues that Cuvier’s principle can be of some use, as long as it is conducted cautiously and in an explicitly evolutionary context.
These days most paleontologists would claim that they aren’t so bold as Cuvier, and that they wouldn’t seriously attempt to reconstruct an animal based upon a single bone (though they certainly might do so for a laugh). I would argue, however, that we’ve actually gone far beyond Cuvier’s wildest dreams. Correlation and exrapolation are largely the name of the game. This is how we sex the brooding theropod, draw out the fetal leviathan, and diagnose the dueling dinosaur.
The much publicized recent discovery of Titanoboa is significant not only because it’s a freaking huge-ass snake, though admittedly it is one ginormous, redonkulus, totally protarded animal. Even more amazing than the snake is what Jason Head and coauthors* do with the fossils. Given a handful of vertebrae from several individuals, they first extrapolate the body size of the animal based on the anatomical proportions found in the largest living snakes, python and anaconda. Then, and this is the really amazing part, they use the size of the snake to calculate paleo temperature based on the relationship between geographic distribution, temperature and body size among living reptiles. In fact, the authors even propose a pole to equator temperature gradient–based on the size and shape of the backbone of an extinct snake!!
If the scientists were simply saying “big snake = tropical weather,” as most news outlets are basically reporting it, that wouldn’t be very noteworthy. But this may be the first time that a fossil vertebrate has been used to calculate a numerical paleotemperature estimate. At last year’s Society of Vertebrate Paleontology Conference I saw one of the authors, David Polly, give a pretty amazing lecture using ankle bone shape to estimate paleoenvironment and paleoclimate.
Taking the temperature of the tropics with a snake – Head et al. 2009
This kind of claim is certain to draw criticism and skepticism within the paleontological community and, probably especially, from neontologists and paleoclimatologists. That’s not neccesarily a bad thing, radical new ideas in science need to be tested. I’m certainly not totally convinced. Still, for a science as old and dusty as comparative anatomy, it’s pretty exciting to see this kind of novel and creative work. It gives me hope that there are plenty of new surprises out there still waiting to be discovered. Cuvier would be proud I think.
For more huge-ass snakes see: Snake Handlin’
* – full disclosure, I’m friends with one of the authors and have worked with him in the field.