Re: ammonites vs nautiloids (was Hell Creek (VERY LONG))

["Colin McHenry" <cmchenry@westserv.net.au>]

>David Marjanovic Wrote:
>
>>Interesting. What I've read (forgot where) is that ammonites had
planktonic
>>larvae (do we know that, actually?), while nautiloids don't, and the
>>plankton was decimated while deeper-sea K-strategists like nautiloids
>>weren't.
>
>Yes we know, because the smallest (presumably newly-hatched) ammonites are
>_really_ small (about 1 mm), while a _Nautilus_ hatchling is about an inch
>across. Another important difference: Nautilus eggs take about a year to
>hatch while ammonites probably hatched quickly. Quite possibly every adult
>Nautiloid and Ammonite were killed at the K/T boundary, but by the time the
>last nautiloid eggs hatched things had settled down enough for a few to
>survive.
>
>Tommy Tyrberg
>

This may be the reason that the marine turtles survived the K/T.  Even if
all adults (usually foraging in coastal waters) got wiped out, there is
usually about five years' worth of juveniles out to sea (sort of like a big
aquatic seed bank), waiting to grow up and come to shore.  If the pelagic
systems were less affected by the extinctions than the coastal systems this
may explain way the turtles, alone of all marine reptiles, were able to
survive the boundary.

Cheers


Colin McHenry
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