randman,
I understand the evo position here very well. Look at your diagram and notice the linear aspect of it. Why wouldn't the black dot start new lineages, for example?
Because that population is extinct. Whether the organism is "similar", or not is a red herring. The salient point is that it is a descendent of the basal population by definition & will therefore already be a member of that phylum, & so will its descendents. No new phylum.
Clearly you have failed to understand the position you claim to know so well.
My comment is that similar forms surely exist which have the potential for evolution.
See above.
Like a squidgy chordate to an elephant, for example? It doesn't matter how similar or different they are, all descendents will be chordates.
For the SEVENTH time:
An organism belonging to a phylum exists within a monophyletic clade. All of it's descendents must therefore belong to that phylum & that phylum alone. It is an artifact of the classification system not the mode & tempo of evolution that limits new clades of high taxonomic rank.
A phylum cannot begat a phylum.
So, if a soft squidgy chordate that is "similar" to the basal population & ultimately evolves into an elephant, the pachyderm remains a chordate. It doesn't stop being a member of that phylum once an arbitrary amount of evolution has occurred.
Why do we always see, assuming common descent, a burst and then from that point in the line, no more?
We don't. I refer you AGAIN to message 75. the only chordates in the early Precambrian were squidgy litle things, a phylum that now includes elephants, whales, fish, amphibians, dinosaurs, mammals & so on.
This is like talking to someone who forgets everything except their name every time they go to sleep. Please try to hold these concepts in your head & ensure your answer takes account of them.
Mark
Edited by mark24, : No reason given.
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