First, the vagaries of algal cell form mean that fossil protists can look different as they are fossilized in various stages of their growth and reproduction. Add to this the different ways in which algal cells can be flattened and distorted during fossilization, and Butterfield finds that a significant number of "species" can be defined by paleontologists, even though all the cells came from only one real species. This bias can only be discovered in a set of fossils that are abundant and "well-preserved", from a single locality at a single time. This is the kind of deposit that Butterfield has analysed. He has shown that a single acritarch (algal) species has already been given at least four different names, and he cites other cases where perhaps 10 or a dozen names have been given to the same organism. By reasonable extension, he argues that the fossil record of Proterozoic protists has likely been magnified as much as 10 times over the biological reality. Add to that the apparent evolution that is another artefact of defining too many species, and Butterfield argues convincingly for a new assessment of Proterozoic biology.
In this new view, there was only low diversity among Proterozoic protists. and their evolution was remarkably slow by the standards we expect to see in Phanerozoic sequences. (Most Proterozoic productivity seems to have been contributed by cyanobacteria.) Proterozoic biology and evolution was "fundamentally different", in Butterfield's words. What happened in the latest Proterozoic and into the Cambrian was a dramatic change in biology and a surge in evolution as "animal" cells and then metazoans appeared, setting off the Cambrian explosion we shall discuss in this Chapter 4 and in Chapter 5.
Reference: Butterfield, N. J. 2004. A vaucheriacean alga from the middle Neoproterozoic of Spitsbergen: implications for the evolution of Proterozoic eukaryotes and the Cambrian explosion. Paleobiology 30: 231252.
Return to Chapter 4
First drafted by RC, October 5, 2004.