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RE: marine reptile McMenu
-------- Original-Nachricht --------
> Datum: Thu, 28 Feb 2008 19:58:13 -0600
> Von: Tim Williams <email@example.com>
> Molecular analyses have suggested that krill (Euphausiidae) appeared
> some time during the Cretaceous period (Jarman, 2001; Biol. J. Linn.
> Soc. 73: 199-212).
This paper simply assumed a strict molecular clock.
So it used a single calibration point: the split between Syncarida and
Mysidacea + Euphausidae, fixed at 350 Ma ago. "This calibration point is
slightly older than the maximum ages of fossil Syncarida and Mysidacea of ~340
Mya because several species of each group were present at this time." (p. 204)
While the use of a single calibration point is mostly due to the lack of a
fossil record for krill (and the lack of good programs for molecular dating in
2001!), the author apparently considers it a feature rather than a bug,
incredibly: "Molecular dating methods are generally considered inaccurate [...]
and especially when they rely on a single DNA region [...]. The use of
calibration points derived from fossil evidence further compound[s] inaccuracy
as a result of the incompleteness of the fossil record." (p. 208)
And even so, only two lineages of krill have survived the K-Pg boundary mass
extinction according to the results (p. 208).
I conclude that there's no evidence for Cretaceous krill, and only negative
evidence against it.
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