Because both are "naturally selected" to swim in water? And thus must have similar body plans? Well fine, allmendream. But you still haven't answered my point about the non-appearance of large numbers of "failed" body plans in the fossil record.
To put it another way, random mutations will not be "selected for" if they do not provide fitness value for survival and self-perpetuation. The fossil landscape should be littered with evidence of creatures whose mutations did not provide fitness value.
Just in the case of fitness to survive in an aquatic environment would require a body plan that is hydrodynamically suitable. "Nature" would have to "select" for this. Fish and dolphins "made the grade." (The first a member of the superclass Pisces, the second, a mammal.) But how many random mutations were there that didn't "make the grade?" Shouldn't there be evidence that they once existed, even if they weren't sufficiently viable in terms of survival fitness in their natural environmental niche to leave many offspring?
Then again, given that evolution reveals very few basic biological body plans, are we to understand this as the result of a long trial-and-error search by Nature to come up with just those few suitable basic forms? If so, we can see the "successes." But where are the "failures" in the fossil record?
allmendream, do you think such questions are meaningless? If so, please tell us why.
Thank you so much for writing!
That is like asking why you don't see failed auto designs on the road. For an animal to be fossilized is a one in a million shot. “Failed” body plans don't get to grow into the million population group, they die young if they are even born at all.
So a non streamlined dolphin born with a big obstruction that drags in the water will not live to produce a large number of descendants among whom a fossil will most likely be preserved.
But a more streamlined dolphin will live to reproduce a more streamlined pack of descendants, and among those one might well get fossilized.
The fossil record is a record of animals that were prolific and successful enough to “win the odds” at being fossilized.