families, biogeography, evolution

[John Grehan]

>Are gondwanian elements elements that show transpacific, transatlantic and
>and transindian relations at the same time, and are restricted to the southern
>hemisphere?

Patterns that show primary trans Atlantic and/or Indian Ocean baselines
conform to Gondwanic distributions. Those that are trans-Pacific do not.

Gondwanic elements (in the sense of having an Indian and/or Atlantic baseline)
are not necessarily restricted to the southern hemisphere.


>I feel like disagreeing somewhat. In my eyes, families or higher taxa are
>rather endpoints of evolution than ancestors.

I see higher taxa as representing the character combination of their
subordinate taxa, so in that sense are the begining. Perhaps in another
sense they are the end.

>As I tried to make clear, effective selection, giving rise to great
>evolutionary
>novelties, should occurr on stages, when there is only one or few lineages.
>I think this is sometimes called the concept of bottleneck.

Perhaps, but from an orthogenetic standpoint this is not the only way
great evolutionary novelties may arise.

>Maybe due to such a bottleneck selection the peculiar and unique apomorphies
>arose which define some higher taxa.

If Croizat's contention that ancestors are widespread relative to the
distributions of their vicariant descendants, then bottlenecks may be
less a primary feature of evolution than many might suppose.

>I agree that it would be interesting to look on how developmental, biochemical,
>ontogenetic or other constraints of the ancestor helped to form
>the unique shape of its descendants. Has this to do with theory of complex
>systems?

I don't know. That's not my field of expertise. Maybe others could comment.

John Grehan