Ediacaran Animals

Rangeomorphs
BBC News OnLine. The paper was eventually published in Science . These are new Ediacaran fossils from Newfoundland, preserved in 3D. Guy Narbonne has presented a simple, elegant and convincing new synthesis of the frond-like animals, the rangeomorphs. They grew by adding units in different ways, so that one complete animal could take on many different shapes and sizes. As with Butterfield's work on Proterozoic protists (Chapter 3), this implies that Ediacaran animals were less diverse than has been supposed. There is a graceless and careless comment in Science from Martin Brasier's group in Oxford. They accept Narbonne's analysis without praising it, and say without discussion that it also applies to later Ediacaran animals that look like Dickinsonia. Then they go into a riff about the potential value of heterochrony to unravel the real truth about these modular Ediacarans. That won't work: here's why. Heterochrony is a powerful incantation to use (6 times in two pages!): the idea covers changes in growth. But "heterochrony" is a description of how change takes place: it does not begin to explain WHY that change takes place. Even if you'd like to have an explicit description of evolution, it's incredibly difficult to pin down which of the array of possible heterochronic changes actually took place in evolution, even in individual fossil creatures that lay down growth-lines to help us understand their growth (molluscs, or brachiopods). It's very much worse in modular creatures such as corals or bryozoans, which can vary the growth rates and growth forms of individuals, groups of individuals, and whole colonies from time to time and from locality to locality, even within the same biological species: and even the concept of biological species can be very difficult to pin down in modular organisms. See Budd, A. F., and J. M. Pandolfi. 2004. Paleobiology 30: 396425. So what Brasier and Antcliffe are doing is waving a magic word that won't unlock any of the secrets of Ediacarans. The future lies in studies such as Narbonne's, which lay a solid pragmatic structure based on analyses of real fossils.

Vendozoa
You might enjoy Ben Waggoner's review of McMenamin's book "The Garden of Ediacara", though I'm sure McMenamin did not.

Page last updated December 4, 2006.

Links last checked, October 1, 2005.

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