RE: FARCICAL: Extinction due to "blue balls"

[Nick Pharris <npharris@umich.edu>]

Quoting "Jaime A. Headden" <qilongia@yahoo.com>:

> While crocs have temperature-dependant sex change, and modern
> birds do not, this does not tell us that all animals leading to birds that
> weren't crocs, including dinosaurs, were not temp-dependant ... it only
> tells us that the change in birds, or the change in crocs from a primitive
> and likely temp-based condition, changed in one of these lineages.

True, though an examination of the nature and extent of the divergence between
the avian W and Z chromosomes could tell us something about the age of the
current system.

Also, just because crocs are temperature-dependent and birds are
chromosome-dependent, it doesn't mean that the avian chromosome-dependent
system evolved directly out of the croc temperature-dependent system.  It could
be that crocs are secondarily temp-dependent, for instance (IIRC, their system
is the opposite from that in turtles).  Or it could be that non-avian dinos
went through any number of chromosome-dependent systems before the current
avian system appeared.

Nick Pharris
Department of Linguistics
University of Michigan