Historylines Metazoa

	Metazoa

	The Metazoa are the animals. Probably the sponges (Porifera) evolved first, although the earliest fossil records are actually of Jellyfish (Cnidaria), which were present in the Ediacaran Era. Most animal phyla with mineralized skeletons made their first appearance (in the fossil record) in the Cambrian, over 500 million years ago, and it seems plausible that many of the phyla which have not left fossil records could have evolved in the Cambrian explosion as well. Kevin J. Peterson believes the first metazoa probably appeared 573-656 million years ago.
	Links about the Metazoa and their Evolution: The Museums of Cape Town have a marvelous introduction to the kingdom of animals (Metazoa) with photographs and descriptions of the various phyla. A page from U Cal Berkeley about the Metazoa fossil record suggests it may be possible that nearly all the phyla of metazoa evolved in the Cambrian aside from the Cnidaria, which evolved earlier, in the Ediacaran (Vendian). Were the Cnidaria present in the Ediacaran Era, or did they evolve later, in the Cambrian. This article from the New York Times discusses fossil and DNA evidence that seem to suggest conflicting dates for Cnidaria (600 MYA or 540 MYA). The Museum Victoria in Australia has a page about the oldest evidence of life, including the earliest animal life. Another possible ancestor of early metazoa would be the bilaterians who lived 580-600 million years ago.

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