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Fruits in the Cretaceous



bk090@freenet.carleton.ca (David Brez Carlisle) wrote:

> There were plenty of fruiting bodies in the Cretaceous ...
> Some forests were dominated by cycads.  Modern cycads
> produce large "fruits" with a pit about as big as that of a peach 
> covered with a brightly colored soft flesh.  The only trouble is
> that they contain a neurotoxin, the casuative agent of Guam disease.
> ... Perhaps a diet
> of cycad "fruits" is the real cause of the extinction of the dinos!

Or, perhaps, frugivory by dinosaurs is the reason modern cycad fruits have
toxins!  Corroboration of this might be if separate groups of modern cycads
have toxins in common, and fossils show these groups split in the Mesozoic,
then we could infer that the toxin probably evolved in the ancestral cycad
in response to whatever was eating it in those days.

Vertebrate neurotoxins are (I think) distinguishable from arthropod
neurotoxins, and if the toxin has a `vertebrate' signature, and the
height and/or structure of the plant made the fruit unavailable to pterosaurs,
then we'd have a good idea it was a dinosaur munching those cycad fruits,
since mammals were too small to use big-pitted fruits, and `birds are also
dinosaurs' :-)

Do paleobotanists/paleoecologists do this kind of analysis?  Or is it too
hypothetical?

Of course, isn't the whole idea of fruits to attract an animal to eat it,
wander off and deposit the seed in a nice pile of fertilizer somewhere?
So, what animals do modern cycad fruits and/or other large-pit thin-skin
fruits attract?

Just to confuse things further, nothing prevents evolution from back-tracking,
i.e. start off making fruits yummy for dinos with poor digestive systems,
then suffering when dinos invent big nutcracking teeth, surviving by becoming
toxic, and then doing without vertebrate dispersal agents forever after.

Mike Bonham        bonham@jade.ab.ca
``So, here I am, sitting by myself, talking to myself.  Now THAT's chaos!''