[Taxacom] minimal estimates

[David Campbell]

Fossils may provide maximum dates as well as minimum dates, but to
figure out any credible date requires actually having some knowledge
of the fossil record, not merely grabbing some dates (or even less
plausibly, some published rate that magically becomes error-free) out
of a reference.  I read a paper not long ago that had merely grabbed
maximum dates out of the Paleobiology Database, yielding some serious
errors due to a misclassified homonym and a wastebasket
misidentification in a paper over 70 years old.  If the taxon of
interest has a very good fossil record (which can be analyzed), it's
likely that the first appearance is not too far after the actual first
appearance.  If the generaly phylogeny of the group is well-known and
well-fossilized, some maxima are readily possible.  E.g., extant
mammal taxa do not diverge in the Paleozoic.

Of course, there are the questions about the degree of linkage between
molecular and morphological divergence dates, calibration of the
fossil record (if your source for dates shows a big gap between the
earliest record and most other records, be suspicious-either the
record is sparse or there's an error).

-- 
Dr. David Campbell
The Paleontological Research Institution
1259 Trumansburg Road
Ithaca NY 14850