Sure they might have existed as rare forms. And statistically they did
exist prior to the first fossil example without a doubt. In general it is
believed that groups exist about 1/3 earlier than the first fossil example.
A 100 myr old creature probably had rare examples 133 myr ago. However, to
push them back too far, say fromthe Cretaceous to the Cambrian would strain
credibility.
>One has to accept that evolution was qualitatively different in that
>formative period. Subsequent evolution is highly constrained, far
>different from the creativity of the Cambrian explosion.
The most reasonable assumption I have heard for the Cambrian is the
possibility that this was when the HOX genes were invented.
glenn
Foundation, Fall and Flood
Adam, Apes and Anthropology
http://www.flash.net/~mortongr/dmd.htm
Lots of information on creation/evolution