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Re: K-Pg extinction global firestorms



Jason Brougham <jaseb@amnh.org> wrote:

> But the idea that "all surviving species were plausibly able to take
> shelter from heat and fire underground or in water" is not obviously
> supported. Crown group birds had diversified by the K-T, and there is no
> evidence that ratites, volant paleognaths, and galliform birds, had any
> such sheltering opportunities.

It's entirely possible that _all_ paleognaths were volant prior to the
K/Pg boundary. "Ratites" are a polyphyletic assemblage of flightless
paleognaths and their last common ancestor was almost certainly a
volant, lithornithid-like bird, which makes the sheltering scenario
somewhat less improbable.

>>Tuinen and Dyke (2004) found that megapodes and possibly cracids had
>>already diverged from the main lineage of galliform evolution by the K-T.

That's because their analysis incorporated incorrect calibration
points (Ksepka 2009). More recent molecular dating analyses support a
post-K/Pg origin of crown-group gamebirds (Brown & van Tuinen 2011;
Jetz et al. 2012), which is much more consistent with their fossil
record.

> Birds that persisted there (in Gondwana) could have recolonized the
> planet. Indeed, that is where ratites are still confined today.

It's true that the origins and early diversification of neornithines
likely took place in Gondwana (at the very least, it would explain the
discrepancy between the molecular divergence time estimates and the
actual fossil record of birds), but the evidence for a Gondwanan
origin of paleognaths is very weak. Given that "ratites" are
polyphyletic and probably became flightless several times
independently, there is no reason to suppose that the breakup of
Gondwana played a major role in their evolution. In fact, ostriches
seem to be a relatively recent migration from Eurasia and a Laurasian
origin of paleognaths as a whole can't be ruled out, either (Phillips
et al. 2010).


*Refs:*

Brown JW, van Tuinen M 2011 Evolving perceptions on the antiquity of
the modern avian tree. 306–24 _in_ Dyke GJ, Kaiser G, eds. _Living
Dinosaurs: The Evolutionary History of Modern Birds_. London: John
Wiley and Sons

Jetz W, Thomas GH, Joy JB, Hartmann K, Mooers AØ 2012 The global
diversity of birds in space and time. Nature 491(7424): 444–8

Ksepka DT 2009 Broken gears in the avian molecular clock: new
phylogenetic analyses support stem galliform status for _Gallinuloides
wyomingensis_ and rallid affinities for _Amitabha urbsinterdictensis_.
Cladistics 25: 173–97

Phillips MJ, Gibb GC, Crimp EA, Penny D 2010 Tinamous and moa flock
together: mitochondrial genome sequence analysis reveals independent
losses of flight among ratites. Syst Biol 59(1): 90–107


-- 
David Černý