What causes species to plateau in the evolutionary process?

Answer 1

That's a pretty tough question, since from an strictly evolutionary standpoint, nothing has really plateaued. Yes it is true that certain organisms appear to be unchanged over millions of years based on their physical attributes, but appearances may be deceiving and merely skin or morphologically deep.

We know that DNA undergoes constant mutation. We also know that most of those mutations are detrimental to the organism. Even then there may be little doubt that the DNA of the most primative living organisms whether archebacteria or some bizarre fish or even crocodiles, has also undergone major changes in one way or another. The reason the phenotype (i.e. their appearance and characteristics) may not have changed or appeared to have plateaued is because those particular phenotypes may still be the survival advantage required or cannot be significantly improved upon... why fix it if it ain't broke?

Also remember that the fossil record only tells us of the general appearance of an organism and gives us vague information about its function. It doesn't tell us anything about its genetic make up, its organ systems, or even if it were warm or cold blooded. Everything else is purely conjecture and educated guesses. So though a modern shark may look like a fossilized one, the insides may be a whole 'nother animal. :)

Answer 2

Lack or elimination of competitive disadvantages.

Answer 3

Anomalies and MUTANTS
A#1