Trilobite: Eyewitness to Evolution by Richard Fortey

Author:Richard Fortey [Fortey, Richard]
Language: eng
Format: epub, azw3, mobi
ISBN: 978-0-307-43467-8
Publisher: Vintage Books
Published: 2000-03-26T16:00:00+00:00

Anomalocaris, at first claimed as a “weird wonder,” but now known to be related to primitive arthropods and hence to trilobites.

But when you reach the scene of crime McCavity’s not there!

The explanation of missing time might apply to some rock sections, like the Siberian ones, but it does not work for eastern Newfoundland where the rocks record a complete narrative. My favoured theory is that the earlier branches in the tree were tiny animals, which were not easily preserved as fossils. It is not necessary to be large to be a perfectly good arthropod (or mollusc, come to that). The sea swarms with tiny arthropods today that have left no fossil record. I like to quote the tiny copepods, which are members of the plankton so numerous that they can turn the seas black. Yet almost their only fossil is a species preserved in the body of a fossil fish. Were it not for their miraculous preservation in amber our knowledge of past insects would be dreadfully inadequate (as it is, we know from amber hundreds of the most delicate of all, mycetophyllids, the fungus gnats, so delicate in life that a puff of wind destroys them). What happened at the base of the Cambrian was probably as much an increase in size as a sudden appearance of new types of animals. This may well have been a genuinely rapid change. We know from many fossils that increase in size is quite an easy goal in evolutionary terms. Mammals, for example, seem to have undergone a very rapid increase in size after the demise of the dinosaurs 65 million years ago. It even seems possible that the same size increase allowed the possibility for the secretion of shells. Muscle support becomes much more crucial when an animal reaches a certain critical size. So the “explosion” was a dramatic appearance of characters that had been rehearsing out of sight for more than a hundred million years.

The explanation just given holds out the possibility of discovery. Maybe one of the readers of this page will discover the Precambrian equivalent of amber. Very recently, a late Precambrian animal embryo was discovered in China, amazingly preserved cell by cell in the mineral calcium phosphate; age by itself is evidently no proof against miracles. It would be wonderful to amaze the world with proof of the missing stages of evolution, tiny animals that set the designs for the future of life. Somewhere, there should be a small trilobite, an animal with the potential for spinning an almost endless variety of costumes for three hundred million years. The search continues.

This is not quite the end of explosions.

There have been several more accounts of the Burgess Shale and the Cambrian since Wonderful Life. Most of the arguments about the truth or otherwise of the “explosion” of phyla have been in the pages of scientific journals, in which a convention of decorousness is observed. Toujours la politesse! Steve Gould knew that I did not agree with his conclusions,

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