Originally Posted by
Jerthunter
So in my opinion primitive does not imply that nothing has changed just that certain characters are not as derived as you see in other groups.
My goodness, stop it or I'll call you out as a cladist!!!!!!!
I think It is important to draw a distinction, IMO, between what evolutionary biologists may think and what "lay" people may think. It is similar to everyone running around shouting "its just a THEORY." Well, lay folks and scientists have a very different idea of what that word means.
Many in the general public look for "missing links" and such and point to so called "primitive" animals as examples. Scientists do not view these in this way. "Primitive" is relative. The example frequently used are stalked crinoids, which currently now only reside in the relatively low predation intensity environment of the deep sea. Prior to the mesozoic, in particular, the were all over the place. It has been hypothesized that the evolution of agile efficient teleost fish ( the so called "mesozoic marine revolution") resulted in the extinction of many groups, or in other terms introduced significant selective pressure. Comatulid crinoids, which are motile, came to dominate, and stalked crinoids were (it is hypothesized) limited to deeper water, lower predation environments.
The fact that they are "primitive" in how WE interpret their characteristics has little significance in the debate.
And my apologies because I have participated in taking this thread off topic. DANG!!