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Re: K-Pg extinction global firestorms



One last note to correct myself.

Two species of angiosperm pollen do apparently go extinct in NZ at the
K-T. But the other forest species apparently all came back, eventually.
There is also one or more fern spikes. Three palynomorphs go extinct at
Seymour Island, Antarctica. Source here is Nichols and Johnson, Plants and
the K-T Boundary, 2008.

So there was an extinction event throughout the southern hemisphere, just
far, far, milder than in North America.

Jason Brougham
Senior Principal Preparator
American Museum of Natural History
jaseb@amnh.org
(212) 496 3544





On 3/29/13 1:15 PM, "Jason Brougham" <jaseb@amnh.org> wrote:

>
>
>>I guess that, in the Roberston et al. scenario we are imagining that the
>>Chicxulub impact happened during a breeding season, and the ancestors of
>>ratites, galliform birds, and the main lineage of neornithine birds were
>>sheltered in their nests at the time of the hypothetical global
>>firestorm.
>>Then, of course, the other hemisphere or areas with a different rainy
>>season that initiated breeding in the local birds would be outside the
>>breeding season, when these birds would not be sheltered. So in those
>>areas all these birds would have been extirpated, and they would have
>>recolonized these areas later from their refugia.
>>
>>Tuinen and Dyke (2004) found that megapodes and possibly cracids had
>>already diverged from the main lineage of galliform evolution by the K-T.
>>Megapodes, of course, could have survived as buried eggs. But cracids
>>nest
>>in trees, and most other galliforms nest on the ground in fairly open
>>settings. Volant paleognaths like tinamous nest in scrapes on the surface
>>of the ground, Lithornis seems to have as well. Tinamous and galliforms
>>nest in open scrapes and also roost with their chicks in trees, and the
>>distribution of this behavior does seem, at first glance, to suggest that
>>it is the ancestral condition.
>>
>>Also, in this scenario we wonder why other groups with the same means of
>>sheltering seemed to go extinct abruptly. Hesperornithiforms,
>>ichthyornithiforms, and other aquatic taxa that could shelter the same
>>way
>>the ancestors of ducks did died out nonetheless. Dyke et al. (2012) even
>>reported an enantiornithine nesting colony beside a body of freshwater.
>>It
>>could just be simple historical contingency, or the extinct groups may
>>have been less broadly (or less luckily) distributed geographically or
>>somehow less biologically resilient.
>>
>>A global firestorm may have occurred, but the complicated computer models
>>that predict this are surely sensitive to initial assumptions and could
>>underestimate one or more factors - energy consumed by precipitation in
>>the ejecta cloud, or energy ejected directly into space, or the extent of
>>cloud cover over the Gulf of Mexico at the time of impact. This is just
>>my
>>own speculation. I just have trouble picturing the forests of end
>>Cretaceous New Zealand burning completely to the ground in one day, then
>>growing back with no species of plants apparently going extinct.
>> 
>>Jason Brougham
>>Senior Principal Preparator
>>American Museum of Natural History
>>
>>(212) 496 3544
>>
>>
>>On 3/29/13 11:52 AM, "Jason Brougham"  wrote:
>>
>>>I think it is a bit premature for us to say that anything is ruled out
>>>at
>>>this point.
>>>
>>>I have not read the Robertson et al. paper, so take my opinion with that
>>>in mind.
>>>
>>>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. These groups do not build burrows that
>>>they
>>>normally shelter in, and they were not divers.
>>>
>>>Moreover, the impact on plant communities seems to have been worst at
>>>the
>>>closest proximity to the impact site (North America), and far less
>>>severe
>>>at great distance (New Zealand). In the latter case there were,
>>>apparently, NO plant extinctions at the K-T boundary. If the Robertson
>>>et
>>>al. model truly predicts a uniform global firestorm, then the model
>>>seems
>>>contradicted by the fossil evidence of the southern hemisphere.
>>>
>>>Jason Brougham
>>>Senior Principal Preparator
>>>American Museum of Natural History
>>>jaseb@amnh.org
>>>(212) 496 3544
>>>
>>>
>>>
>>>
>>>
>>>On 3/29/13 10:56 AM, "Richard W. Travsky" <rtravsky@uwyo.edu> wrote:
>>>
>>>>
>>>>
>>>>On Wed, 27 Mar 2013, Ben Creisler wrote:
>>>>>
>>>>> A new paper of interest:
>>>>>
>>>>> Douglas S. Robertson, William M. Lewis, Peter M. Sheehan & Owen B.
>>>>>Toon
>>>>>(2013)
>>>>> K-Pg extinction: Reevaluation of the heat-fire hypothesis.
>>>>> Journal of Geophysical Research: Biogeosciences (advance online
>>>>>publication)
>>>>> DOI: 10.1002/jgrg.20018
>>>>> http://onlinelibrary.wiley.com/doi/10.1002/jgrg.20018/abstract
>>>>
>>>>So, what about the other recent news that it could have been a comet?
>>>>That 
>>>>has a different composition from, say, an asteroid. It would seem to
>>>>rule
>>>>out a comet.
>>>
>