[shaki-dora]

Note that “the oldest species of <x>” doesn’t make any sense. Both that species as well as its closest evolutionary relative have a last common ancestor, meaning they are equally “old”.

Do this a few times and you will notice all species have the same “age”, assuming life today all descendent from a common ancestor. Yes, some of them have may have changed more or less in appearance, but that correlates poorly with genetic changes.

[wtracy]

"Oldest" in the sense that it has existed (as far as we can measure) in it's current form longer than any other species.

You can't say that a species is as old as it's ancestral species, because you're talking about two different species.