Gondwanan distribution of young taxa

Mon Feb 24 11:26:28 CST 2003

I suggest Winkworth et al. 2002. "Plant dispersal N.E.W.S from New Zealand" in Trends in Ecology and Evolution 17 (11): 514-520, might be worth a look. Other unpublished or in press reports from New Zealand largely back up the view presented therein. DNA sequence analysis strongly suggests that a number of New Zealand plants are recently diverged from Australasian or South American relatives. In some cases, the groups involved probably have mid tertiary or earlier origins, such as that described for Spermacoce, but species pairs or groups distributed across oceans have much more recent common ancestors. Some groups, such as Gnaphalioid daisies, are distributed widely on southern continents and appear to have dispersed on multiple occasions to New Zealand. 
Although Ken Kinman is astute in his observation that "taxa are usually older than we might think they are", he seems to have in mind lineages corresponding to taxa above species level.  When examining distributions within such a lineage, it is important to remember that extant species could be the product of radiations much more recent than the divergence of the generic lineage from others (by analogy, short twigs at the end of a long branch). 
A conclusion that long-distance dispersal has been important in bringing about present day distributions is forced on us for a number of groups that look like unlikely dispersers as well as many with obvious adaptations to long dispersal distances.
 Like Ken Kinman I think Antarctica may have played an important role in the history underlying present day distributions of Southern biota, however the Late Tertiary may be more relevant than the Oligocene.

Rob Smissen

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