Quote:
Originally Posted by Pyrotex
That, in a nutshell, is how and why body plans can only be created at very early stages in the evolution of any creature. At a stage when no superstructure has been built upon, and is tightly dependent upon, a certain number of: legs, segments, vertabrae, eyes, whatever. But after that superstructure has evolved, the body plan underneath is "frozen in" and cannot change.
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Thank you, Pyrotex. Your post makes brilliant sense and it's really well explained
I'm wondering if it is possible in your estimation for another body plan explosion to happen today. Of course, it wouldn't happen as you say with one of the more complex phyla. But, with one of the early branches of the animal tree like a sponges or flatworms—sponges don't have nervous, digestive or circulatory systems and their cells are very unspecialized—might they find themselves in a position one day to branch out into a new assortment of body plans?
My first thought is that this is more unlikely today than it was in the pre-Cambrian because competition is greater now. There aren't as many vacant niches in the ecosystem which would drive such a change. Why, for example, would a sponge develop legs to scurry around the ocean floor if crabs and lobsters are already expertly filling that niche?
But, it might be just as likely (and I frankly am not informed enough to know) that sponges and other simple animal phyla are not genetically in a position right now for a body plan explosion. Perhaps one day a species will come to a point where evolving new body plans is easy and favorable.
I'm curious what you think.
~modest
