At the library today, I read that there are no fossils of jawless fish...and a question formed in my mind:
What if there are no jawless fish fossils (in the Jurassic or whenever) for the simple reason that there weren't any.
Now I'm not suggesting that the existance of jawless fish is a scientific hoax, the likes of which would put Piltdown to shame.
No, I'm just wondering if what we call jawless fish - lampreys and hagfish - are actually members of more recent groups of fish. Its fairly common for species to simplify themselves as they become more and more parasitic (or for other specializations, examples of which escape me at the moment)...think of male anglerfish. Might jawless fish simply be an extreme example of hyperspecialization?
I realize I'm probably wrong, but I thought it was interesting, and I hope you did too.
Coincidence or not, today, I started wondering about fish. What if, back in the heyday of the lobe-finned fishes, all the ray-finned fish had gone extinct?
I fear that the sharks would seize most of the niches before the lobe-fins would get to them. Therefore, lets add the sharks to the ranks of groups to wipe out in this thought experiment. (as well as any other fishes I've forgotten to mention)
Squids and their ilk might seize the opportunity, feasting on some of the lobe-fins. But Acanthostega and Eusthenopteron wouldn't go quietly, I can tell you that.
Hmm...would the squids seize and hold the niche of large-bodied marine predator (presently held by sharks and orcas) ?
Would this at all delay or prevent the colonization of the land by the lobe-fins?