ubiquity said:
any info on relations between prehistoric cephs and prehistoric whales?
Hmm.......having a tenous crack at this one....
Well certainly the late Eocene toothed whale
Basilosaurus has been found with squid stomach contents, though it has also been found with the remnants of shark, perhaps demonstrating that it had a somewhat non-exclusive and opportunistic diet.
Basilosaurus was an extremely long and serpentine creature stretching almost 40 meters from head to tail. It lived roughly 40-38 million years ago and fossils are known from Egypt, very close to the Valley of the Kings near Cairo, of all places!
It is generally thought, I think, that the mystecetes (baleen) whales radiated from the basilosaurids early in the subsequent Oligocene period (35-23 mya), leaving the basilosaurids to evolve into the odontocetes or toothed whales we know today. Precisely how closely related the modern three species of Sperm Whale are to
Basilosaurus would be interesting to find out.
The point is, it seems to me that giant squids were prey to large carnivores right up until the end of the Cretaceous when the large marine reptiles died out in the along with the dinosaurs and many other forms of marine life (65mya). There was then a huge gap of 25 million years when gigantic forms of cephalopods,
if they existed, would have been relatively free of predatory attack. In the adult stages creatures such as
Tusoteuthis or
Architeuthis would have been fairly safe as there do not appear to be any large marine predator that would have been capable of taking them on, except possibly sharks.
I am speculating here but I doubt if
Tusoteuthis is the direct ancestor of
Architeuthis simply due to the paucity of evidence of large fossil squid in the intervening 80 million years. It seems likely that large squid pens from the intervening period would have been found by now. Admittedly the fossils may be out there and we simply have not discovered them yet, but their absence could demonstrate that they were not present and that large squid evolved at least twice in unconnected families, one in the late Cretaceous and one fairly recently. Could it be that Cretaceous extinction event wiped out the prehistoric giant squid leaving the cephalopods to exploit this niche at a later time?
Perhaps one could surmise that to attain a large size through rapid growth rate would be a useful evolutionary end during this hiatus of large marine predation. Smaller squid sizes are vunerable to be eaten, perhaps the growth of
Architeuthis' and
Mesonychoteuthis' ancestors to an extreme size was a direct result of being able to exploit this safer ecological niche.
Again, if anyone knows of any large fossil squid in any fossil deposit, I'd love to hear about it.
This is purely my own speculation, so please feel free to shoot it down!