>I won't tell you it is because of niches. But I will tell you that you are
>wrong. Here are the phyla that have appeared since the Cambrian. Some of
>them are quite major.
>
> Dinoflagellates Triassic
>Calcareous nanoplankton Triassic
> Diatoms Cretaceous
> Bryophytes Late Paleozoic
> Psilophytes Middle Paleozoic
> Lycopods Silurian
> Sphenopsids Devonian
> Ferns Devonian
> Cycadeoids Middle Paleozoic
> Ginkgos Early Mesozoic
> Conifers Late Paleozoic
> Angiosperms Early Cretaceous
> Bryozoa Ordovician
>
>You are going to now say 'Animal phlya' is what you meant. But you didn't
>specify this in your note above. Phyla have appeared since the Cambrian.
>And now some phyla are found before the Cambrian like Sponges and molluscs.
>glenn
'Animal phyla' is what I meant. That was the context, unless I overlooked
plant cell types in the tabulation you offered. But even in terms of the list
you give here, the point remains, that major phyla were formed early and
no new basic plans have formed since, and our general evolutionary theory
does not predict this.
--Cliff Lundberg ~ San Francisco ~ cliff@noe.com