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Re: Question: K/T r vs. K regimes



>Do you think the physical fragility of K/T birds was a liability vis a vis
>other classes of land vertebrates (esp. mammals) in the post-K/T r regime?
> Wouldn't the metabolism and power of flight be a big advantage in an r
>regime after shift in primary selection from a K basis?  I'm sure there were
>still dinos the year after Chicxulub.  But their 150MY+ trait adaptations
>were far better suited to K than r, and the tops of the food chain are
>longest-lived as well as biggest, and can't adapt as quickly in the face of
>rapid changes in the ecological carrying capacity or in
>same-capacity-different-habitat changes.

Unlike large mammals, dinosaurs were r selected - they had phenomonal rates
of replacement (i.e., annual clutch size).  Whereas an elephant needs two
years or so to gestate a fetus, an elephant-sized dinosaur could lay a
couple of clutches with dozens of eggs each in the same time.  Therefore,
there is no real basis to refer to the Mesozoic as a "K selected" time.

>In 500 years they get 10-20
>generations; the (small) birds and mammals get 100-500+ (how do those shrews
>do it?).   Not to mention that in famine, the top of the food chain can be
>lopped off altogether - eg Australia's limited fauna (Jared Diamond wrote an
>interesting article on the topic a year or so ago in Discover, I think).

That is dinosaurs true weakness - the amount of food they need.  They could
replace themselves much more quickly than large mammals or birds.  But even
a cold-blooded dinosaur would require a whole lot more food than a small
mammal or bird, and a hot-blooded one much more.  So, dinosaurs should have
been able to repopulate very quickly after hard times, but required much
greater amounts of food to make it through hard times.

>
>It would be interesting to know the # of sub-10kg bird vs. mammal vs. dino
>species present in latest Cretaceous strata.  They were all fragile; were
>they comparably fragile, or is the record skewed by differences between
>classes?

It certainly would.  However, the latter question is currently untestable
(since fossils are the only record of these species, how can we tell is the
proportions are real or skewed?).  As far as we no, there are no sub-10kg
dinosaur species during the latest Maastrichtian, as even dromaeosaurids,
elmisaurids, hypsilophodontids, etc., were larger than that.


                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.