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re: K-Pg extinction global firestorms




>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.
>>