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

What about reproductive rate?  Large animals with low birth rates and long 
generation times may have had more survival difficulties than smaller animals 
with lager broods, adapted to conditions under which infant mortality was high. 

Ronald Orenstein 
1825 Shady Creek Court
Mississauga, ON
Canada L5L 3W2

> On Nov 23, 2015, at 7:29 AM, Thomas R. Holtz, Jr. <tholtz@umd.edu> wrote:
> 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 survivors. Was this
> 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
>> Sent: Monday, November 23, 2015 6:43 AM
>> 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