Ancient Soft Parts: Dinosaur and Elephant Tales

Some of my colleagues are downplaying the recent paper in science showing a: that mastodons are elephants and b: that birds and dinosaurs ... in particular Tyrannosaurus rex and turkeys ... are related. (See here and here, for instance)

Yes, it is true that these phylogenetic findings are wholly uninteresting, being exactly what we expected. But that is WHY these particular phylogenies were carried out.

You see, the research is being done with organic material that is very very old, and is amazingly, remarkably, unexpectedly and astoundingly preserved. The point of using this material to test a phylogeny that we already know is actually to test the material ... the organic stuff in the 'fossils' ... to see if it is for real.

And yes, indeed, it is. Bits of rotted flesh from a mastodon and an old dinosaur exist. Ick.

Here are the ancient elephant and the dinosaur resting comfortably on their phylogenetic laurels:

So the palaeontology world appears to be agog at this remarkable find, but really, the persistence of biomolecules from ancient material should not be all that surprising. Let me explain why.

Fossilization involves the degrading of biomolecules (including proteins) and their replacement with other molecules, such as minerals brought to the site of degradation by water. Subsequently, these minerals may be further modified through dissolution in water and replacement, crystal growth, or other means. This is a long term process. Those of us who tend to dig up bones and stuff that are less than a couple - few million years old do not really expect every bone to be a fossil. In fact, the bones that I've excavated from Kromdraai, in South Africa, mostly seem un-mineralized to me, while other bones from younger sites can be very mineralized.

It is a slow, stochastic process.

The initial processes that occur to a newly dead organism are of course very quick. The flesh is gone from the bones, the grease leached out, connective tissue gone, in a single rapid step (in geological time) and this rapid taphonomic moment (but see below) is followed by often slow and steady mineral replacement. So as a rule, everything turns quickly, very quickly, into bones, but then slowly, sometimes very slowly, into true fossil (with the minerals replaced). But since this second step is slow and stochastic, we know there must be some bits of original bio-stuff here and there among the fossils that simply has not yet been converted, even in fossils that are millions of years old.

It is also true, but the way, that this initial step of conversion from furry elephant or scary thunder-lizard king dinosaur to a pile of bones may also be rather slow. Many dead things actually turn into mummies rather than piles of bones. Mummification involves the dessication of the flesh in such a way that the entire process is very much slowed down. Effects other than mummification can occur as well, including water logging in anaerobic environments. These effects can cause the first several million years of a "fossil's" journey to the paleontological specimen drawer to be traveled with relativity minimal loss of the original bio-molecules.

So it is not really a surprise, but it is very very cool, that Organ et al. were able, as described in this paper, to make hay out of old flesh.

Organ, C.L., Schweitzer, M.H., Zheng, W., Freimark, L.M., Cantley, L.C., Asara, J.M. (2008). Molecular Phylogenetics of Mastodon and Tyrannosaurus rex. Science, 320(5875), 499-499. DOI: 10.1126/science.1154284