[Taxacom] Hedges/Kumar (eds) The Timetree of Life

[Kenneth Kinman]

Hi guys,
       With respect to the "transatlantic" rodents (phiomorphs and
caviomorphs), I wouldn't be surprised if "they dispersed over water".
However, I would be surprised if this happened directly and over a wide
gap from Africa to South America.  
       Seems more likely that the dispersal was more indirect (south
through Antarctica or north through Europe, via eastern North America).
Who knows, the common ancestor of these rodents may have even originated
in Antarctica (the fossil record of which is sparse at best).  In which
case, you could argue that it was vicariance.  At this point, who knows.
       HOWEVER, in the case of Crocodylus, I strongly suspect a much
later disperal, and that it WAS directly from Africa to South America.
Therefore, I doubt that the fossil record will shed much light on that
debate.  Seems to me that a Late Miocene or Pliocene Nile crocodile
would have been able to make that long-distance dispersal directly from
Africa to South America, but I am much less willing to accept such a
direct dispersal of a caviomorph-phiomorph rodent when other hypotheses
(less direct geographically) seem more likely.  When it is less direct
(and happened earlier in time), the distinction between vicariance and
shorter distance disperal (or both) get very murky, especially given the
sparse fossil record in Antarctica. 
          -------------Ken Kinman