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

["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 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