[Taxacom] NZ biogeography - fossil dating

John Grehan calabar.john at gmail.com
Wed Nov 2 12:48:37 CDT 2016

For those interested, another excerpt (and contingent on any typos on my

p. 47

“Most groups are not represented in the fossil record at all, and even
large, family-level groups can be absent in the fossil record over large
areas. If the 108 angiosperm families indigenous in New Zealand, 33 (31%)
are either not recorded in the country’s fossil record at all 919 families)
or have Pleistocene fossil only (14 families) (Lee et al., 2001). The
fossil record in most of the other families is probably also very deficient.

Recent work has developed the idea that the age of a clade does not equal
the age of its oldest fossil; in other words, the fossil record cannot be
read literally. In an extinct clade, the youngest fossils predate the
extinction (Signor and Lipps, 1982). Likewise, the oldest fossils of a
clade postdate its origin and only give a minimum age for the clade. This
has been termed the Sppil-Rongis effect (the converse of the Signor-Lipps
effect). Dornburg et al. (2001) noted “the tophonomic bias in the fossil
record (Sppil-Rongis effect) increases the probability of fossil
preservation toward the present, with large gaps often artificially
truncating the distribution at deeper time scales.”

Despite this limitation, the authors of the Modern Synthesis accepted that
the fossil record provides the best source of information on evolutionary
chronology, or even the only source (Simpson, 1944).  Recent authors have
agreed “molecular clocks require fossil calibration…Directly or indirectly,
all molecular clock analyses reply on paleontological data for calibration”
(Donohue and Benton, 2007). “For any molecular dating study, a basic
requirement is at least at least one fossil constraint to anchor the
estimated divergence times onto the timeline of the Earth” (Hug and Roger,
2007). “Fossil calibrations are essential when dating evolutionary events”
(Wilkinson et al., 2011).

John Grehan

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