Hi, Peter.
Peter writes:
What evidence (of anything related to evolution) do transitionals represent if they are NOT related in a pre-post sense?
They
are related, but not necessarily as direct descendants.
Let's play with a hypothetical scenario.
Let's say we have a handful of fossils from millions and millions of years ago.
And, let's say that these fossils represent three species of animals that belong in the same genus.
And, let's say that we can tell, from their characteristics, that they are related to mammals.
However, they are so similar to one another, that it isn't clear which (if any) of the three species is an actual ancestor of mammals.
Also, we don't have
any fossils that can link mammals to any particular one of these three species.
And, we don't have
any other fossils of organisms that might be a better fit for the ancestor of mammals.
What steps can we take to determine which (if any) of these three species is the actual, lineal ancestor of mammals?
I don't think there is much we can do about it, other than to keep looking for other fossils that might shed light on the issue. So, in the absence of good evidence either way, we conclude for each of these three species that they either
are the actual, direct ancestors of mammals, or they are sufficiently closely related to the actual, direct ancestors of mammals to be used as approximate surrogates for the ancestors in demonstrating the evolution of the mammal lineage.
For the sake of propriety, paleontologists have made it a habit to assume that any transitional fossil is just a surrogate, rather than the actual ancestor, because this is a less extreme claim.
So, to answer your question directly, yes, "transitional form"
does bear a connotation of direct relationships. However, sometimes scientists are forced to approximate these direct relationships using surrogate species that are closely related to the direct ancestors, and these are also "transitional forms."
Edited by Bluejay, : Shortened by removing a major redundancy
-Bluejay (a.k.a. Mantis, Thylacosmilus)
Darwin loves you.
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