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Re: Prehistoric Plankton Predators (PPP for short)



.>Are there any giant plankton-feeders from the Mesozoic?
The giant Pachycormid  Leedsichthys problematicus  from the  Oxford clay
formation ,Middle Jurassic of England ,was probably the largest Mesozoic
planktivorous fish,  with a suggested size of over 20 metres in length.A
Leedsichthys caudal fin  in the Natural History Museum , London  collection
is around 3 metres in height .Leedsichthy is understood to have been
analogous to the recent baleen  whales and filter feeding sharks.
> I cannot believe that the oceans of the Mesozoic were plankton-deficient.
Do not forget that the Cretaceous chalks deposits are  composed from
remains of calcareous nannoplankton, however modern plankton contains a high
percentage of  organisms with low preservation potential , if the
depositional environment was not ideal for fossilization you won't find
them!
>Large peaceful plankton-feeders could not evolve until they were wiped out
after the K-T
Some of the Plesiosaurs  such as  Cryptoclidus had  numerous sharp thin
teeth and may have used them for straining  small prey such as crustaceans,
but no true large suspension feeding reptiles are known, as far as I
know.Try and get a copy of Ancient Marine Reptiles  (Academic Press) and
look at the chapter on 'Constraints on Tetrapod Feeding Mechanisms' that
explains why marine reptiles never became suspension feeders like the baleen
whales.
The position of giant suspension feeders  during the Mesozoic was therefore
probably held by large fish and Sharks, the latter have a poor preservation
potential due to there cartilaginous skeletons whilst the former would have
been broken up easily by predators/scavengers or currents,Leedsichthys is
usually found as disarticulated  elements scattered over a huge area.
Nick Oliver.
O.U Undergraduate student, Earth Sciences.
----- Original Message -----
From: "Dino Rampage" <dino_rampage@hotmail.com>
To: <dinosaur@usc.edu>
Sent: Saturday, November 23, 2002 3:41 PM
Subject: Prehistoric Plankton Predators (PPP for short)


> Are there any giant plankton-feeders from the Mesozoic? It really seems
odd
> to me that throughout the Mesozoic, no animal seemed to take advantage of
> the plankton & grow to a huge size. Just look at our modern-day oceans:
> Among the elasmobranchs we have the Whale Shark (Rhincodon typus) the
> Basking Shark (Cetorhinus maximus) & the Megamouth Shark (Megachasma
> pelagios) the various species of Mobula & Manta rays, (Mobula sp. & Manta
L
> sp.) The teleosts have provided us with the Ocean Sunfish (Mola sp.), and
> let's not forget the 10-13 species of Mysticete or baleen whales.
>
> If our modern oceans can support such a wide diversity of giant plankton
> feeders, why not the oceans of the Mesozoic? Surely the oceans then were
> just as bountiful; I cannot believe that the oceans of the Mesozoic were
> plankton-deficient. Or were the predatory marine reptiles & sharks so
> successful that large peaceful plankton-feeders could not evolve until
they
> were wiped out after the K-T?
>
>
>
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