RE: K-Pg extinction global firestorms

[Jason Brougham <jaseb@amnh.org>]

Thank You, Mr. Cerny, for drawing my attention back to Living Dinosaurs (2011). 
It is an excellent resource, and it was Bent Lindlow that I can credit for 
first writing "the IR thermal radiation model is simply too lethal." His 
criticisms of the Roberston et al. hypothesis were very influential on my 
thinking. Thanks also for the Ksepka reference, I had not read it.

David Cerny wrote:

>It's entirely possible that _all_ paleognaths were volant prior to the
>K/Pg boundary. 

agreed

>"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.

Yes, "ratites" are paraphyletic, as this grouping excludes the tinamous. 
"paleognaths" may be a more useful grouping. I agree that it makes the 
sheltering scenario 'less' improbable, but it is still highly improbable as 
basal birds (palaeognaths, incl. tinamous, and non - megapode galliforms) show 
a highly conserved and almost uniform use of simple scrape nests. (other than 
the nocturnal and almost certainly derived Kiwi). And according to Phillips et. 
all (2009) four separate paleognath lineages survived the K-T event. Do we 
really think it most likely that breeding populations of three ancestral 
ratites and one ancestor of moas and tinamous all survived in burrows or tree 
cavities at the time of impact? And even if we do, could those populations have 
survived after emerging into habitats that were now burned wastelands?

>>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.

That makes sense, thank you for the ref. But we must be careful in putting the 
notoriously sparse fossil record foremost, despite all its missing data. 
Otherwise we could get into another "temporal paradox" theoretical dead end. As 
your reference, Brown and van Tuinen (2011) note in figure 12.1, anseriforms 
and  galliforms may have diverged 80 mya. Depending on what fossil you take to 
be the oldest true galliform, that may leave fossil gaps of 30 million years or 
more.

> 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).

Your reference of Phillips (2009) states that a south Gondwanan origin for all 
non - ostrich paleognaths is unequivocally supported. But it does also find 
that ostriches complicate matters. Gondwanan origin is apparently always 
favored in Maximum Likelihood analyses, but they note that a Northern 
Hemisphere origin is possible and is apparently favored by Maximum Probability 
analyses (that they did not include) if we include ostrich fossil data. That is 
fascinating. But, again, I am skeptical that the fossil data give us a reliable 
signal because the ostrich lineage has a fossil gap of some 40 million years! 
If we bear in mind that bird fossils are extremely rare and that the record is 
skewed, it is wholly plausible that Lithornithids and/or Palaeotididae (in 
which Mayr included Remiornis) simply dispersed into Eurasia after the K-T, and 
that ostriches could have arisen in Africa and dispersed into Eurasia along 
island chains, a route has been hypothesized for lacertid lizards (Hipsley et 
al., 2009, BMC Evolutionary Biology).

In any case, my reasoning did not really require that all palaeognaths 
originated in Gondwana. It simply noted that they may have survived in refuges 
very distant from the Chicxulub impact site. Southeastern Asia was probably as 
distant from Chicxulub as Patagonia was at the end Maastrichtian (Jeroen Trump, 
Princeton, in simulations published here: 
http://www.princeton.edu/main/news/archive/S31/90/32S94/). If some paleoganths 
found refuge from the impact in east Asia I would not be at all surprised. 




*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