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RE: Why non-avian dinosaurs weren't able to survive

The recent paper by Sallan and Galimberti found that, after the Devonian mass 
extinction, there was selective pressure for smaller body masses for 36 million 
years! It did not correlate to oxygen levels or temperature, suggesting it was 
ecological: faster generation times, smaller food requirements.

When I read that I remembered that terrestrial Paleocene faunas stayed small 
long after the impact.

From: owner-DINOSAUR@usc.edu [owner-DINOSAUR@usc.edu] on behalf of Augusto Haro 
Sent: Monday, November 23, 2015 9:35 AM
To: tholtz@umd.edu
Cc: dinosaurtom2015@seznam.cz; Dinosaur Mailing List; Ben Creisler
Subject: Re: Why non-avian dinosaurs weren't able to survive

Size seems to be a good reason for most dinos and other large animals
becoming extinct. They needed more food, and less was available. The lower
productivity by the plants also implied lower [O2], and given the lower
surface/volume ratio in large animals (which implies proportionally lower
respiratory surfaces), they were more likely less able to gather the
necessary O2. I think small animals were however also strongly hit when
relying too much on vision, likely because of the dust cloud. This may
explain why a single lineage of birds survived, whereas many more among
mammals (which rely proportionally more on olfaction) did. Given the low
amount of light reaching the sea depths, this may also explain the strong
effect on the ammonites if they were as strongly relying on vision as the
Recent Coeloidea.

Dr. Augusto Haro
Museo de Paleontología
Universidad Nacional de Córdoba
Vélez Sársfield 249
Córdoba, Argentina
TE: +54 351 4332098, int. 256

2015-11-23 9:29 GMT-03:00 Thomas R. Holtz, Jr. <tholtz@umd.edu>:

> Many different possible answers, but at present we can't tease out which
> one(s) is/are correct:
> * On land, there is a strong size bias at the K/Pg boundary. On average
> non-avian dinosaurs were larger than the survi
> due to:
>  --smaller absolute amount of food available, so that larger endothermic
> animals simply didn't have access to enough food?
> --inability to hide from the thermal pulse in the minutes/hours after
> impact?
> --inability to hide in warm spots during Impact Winter?
> * Also, the larger body size but small birth size meant that non-avian
> dinosaurs went through more growth stages ecologically than
> most contemporaries. If any one of these turned out to be vulnerable, the
> species would go extinct. (Fowler's hypothesis).
> * Crocodilians fed from the freshwater ecosystem; many branches of Aves
> already present fed from the marine ecosystem. Both of these
> have a "pantry" in the form of bottom-feeders with access to food not as
> directly tied into the immediate photosynthetic pathway. In
> contrast, the sun -> plant -> herbivore -> carnivore pathway on land and
> its equivalent in the pelagic realm were very strongly
> affected; non-avian dinosaurs (and hesperornithines, and maybe the Late K
> enantiornithines) were part of these pathways.
> So there are many possible reasons.
> Thomas R. Holtz, Jr.
> Email: tholtz@umd.edu         Phone: 301-405-4084
> Senior Lecturer, Vertebrate Paleontology
> Office: Geology 4106, 8000 Regents Dr., College Park MD 20742
> Dept. of Geology, University of Maryland
> http://www.geol.umd.edu/~tholtz/
> Phone: 301-405-6965
> Fax: 301-314-9661
> Faculty Director, Science & Global Change Program, College Park Scholars
> Office: Centreville 1216, 4243 Valley Dr., College Park MD 20742
> http://www.geol.umd.edu/sgc
> Fax: 301-314-9843
> Mailing Address:        Thomas R. Holtz, Jr.
>                         Department of Geology
>                         Building 237, Room 1117
>                         8000 Regents Drive
>                         University of Maryland
>                         College Park, MD 20742-4211 USA
> > -----Original Message-----
> > From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] On Behalf
> Of Poekilopleuron
> > Sen
> > To: dinosaur@usc.edu; tholtz@umd.edu; bcreisler@gmail.com
> > Subject: Why non-avian dinosaurs weren't able to survive
> >
> > Good day,
> >
> > I would like to make myself clear about what is the actual scientific
> opinion on this question. How is it possible that very
> similar
> > creatures in ecological and physiological sense, i. e. birds and
> crocodiles, survived into the Cenozoic, while non-avian dinosaurs
> could
> > not? Given that some of them were endothermic (?), cursorial, fossorial
> and equipped with a feathery integument, why they didn't
> > make it into the new era? Were mammalian and bird survivors "better" in
> something, did they have more "usable"
> > adaptations or were they just less specialised and more resilient? Thank
> you, Tom