[Taxacom] biogeography and fossil absence

[John Grehan]

Fossils are all too often misrepresented piece of evidence in biogeography,
mostly because so many biogeographers ‘forget’ that the oldest fossils only
give the age of the oldest fossil. Or maybe it's just plain denial as the
authors of one publication noted the objection to extrapolating fossils to
maximal dates and then just went on ahead with it anyway as if nothing were
said.


Below is an example on age and fossil absence from "Biogeography and
Evolution in new Zealand" (p.101).


“Many molecular studies still depend on a similar method of interpreting
the fossil record in order to calibrate phylogenies and establish which
groups can, or cannot, be Paleozealandic (Wallis and Trewick, 2009). For
example, Wagstaff and Breitwieser (2002) reviewed molecular studies on New
Zealand Asteraceae. The concluded: “New Zealand separated from Gondwana
some 80 million years ago and was isolated by the southern oceans for a
bout 40 million years before the Asteraceae first appeared in the fossil
record. Hence each of the major clades of New Zealand Asteraceae may relate
to dispersal events across and oceanic barrier.” (This can be compared with
the Bayesian study of the family by Swenson et al., 2012, cited in Chapter
2.)


In the Asteraceae, lack of recognized fossils from the Mesozoic meant that
the breakup of Gondwana was assumed to have no direct relevance. Yet there
are many reasons why a group that is diverse and abundant now might not be
preserved or recognized in the Mesozoic fossil record. Basing assumptions
about age of this absence is dangerous and unnecessary. In any case, recent
studies indicate that Late Cretaceous fossils (76-66 Ma) belong to an
extant genus of Asteraceae (Barreda et al., 2015), confirming the
predictions made by biogeographers.”