Monday, August 08, 2005

Bilateral Symmetry and the Cambrian Explosion

This is cool.

Bilateral symmetry is a character of most organisms (except sponges, jellyfish, ctenophores and echinoderms). According to my book on vertebrate structure (An Analysis of Vertebrate Structure, 2nd ed, by Milton Hildebrand) this is a fundamental characteristic of vertebrates. A 2004 discovery has pushed the origins of bilateral symmetry back to approximately 600 million years ago - to the Precambrian.

From the article:

The discovery is crucial. It suggests that the earliest ancestors to modern-day animals developed before the Cambrian explosion. That so-called explosion period, 488 to 542 million years ago, envelops the time on Earth when most animal groups first appeared.

In his article, Bottjer suggests that the famous Cambrian explosion was more accurately "the exploitation of newly present conditions by animals that had already evolved the genetic tools to take advantage of these novel habitats."

Rather than solely genetics, it may have been the critters' ability to grow large that led to the explosion. The growth spurt, Bottjer said, may have been caused by a drastic rise in dissolved oxygen in seawater. More oxygen for breathing reduces size constraints.
(emphasis mine - afarensis)

Even more interesting is the process underlying the discovery:

But it took incredible patience and work to uncover the fossils, which measure about 200 micrometers across. The team sliced the samples into thousands of see-through-thin layers and examined them under a microscope. Finally, among the 10,000 slides, the collaborators discovered 10 examples of the fossil type they had been seeking. After more months of painstaking analysis, the group confirmed the examples were fossils of miniscule bilaterian animals.

So after plenty of hard work a phenomenal new discovery was made - one that throws some light on Precambrian life and the Cambrian explosion. Another talking point knocked out from beneath ID proponnents.

Teach the Controversy says I.

Note: those of you with a digital subscription to Sciantific American can go here for more info