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Re: K/T revisited, was: Re: DINOSAUR digest 3382
Peter Ward (and others) believes that ammonites went extinct because they
bred/fed at shallow depths. In contrast, he claims that nautaloids
survived because they bred/fed in deeper water. I'm don't know what his
take is on squids and octopus.
The hypothesis is that the deeper depths were "buffered" from the carnage
that was occurring in the near-surface marine waters. This idea is
supported by the observation that Maastrichtian benthic biota tended to
fare a little better than did their pelagic counterparts.
The explanation I've read is that, unlike nautiloids and coleoids, ammonites
had planktonic larvae (known in the fossil record as "ammonitellae"), and
that the plankton was largely wiped out. This would also help to explain the
complete extinction of the rudists and inoceramids (which, in addition, most
probably fed on plankton). Didn't the corals (which also have planktonic
larvae) need the entire Paleocene or so to form the first full-size Cenozoic
Is anything known on the belemnite life cycle...?