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Re: Dinosaur egg-laying contributed to extinction?



The paper is now out. Here is the abstract  from 
http://rsbl.royalsocietypublishing.org/content/early/2012/04/12/rsbl.2012.0240.short?

Ontogenetic niche shifts in dinosaurs influenced size, diversity and extinction 
in terrestrial vertebrates
        • Daryl Codron1,2,3,4,*, 
        • Chris Carbone5, 
        • Dennis W. H. Müller1 and
        • Marcus Clauss1

+Author Affiliations

        • 1Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, 
University of Zurich, Winterthurerstrasse 260, 8057 Zürich, Switzerland
        • 2Florisbad Quaternary Research, National Museum, PO Box 266, 
Bloemfontein 9301, South Africa
        • 3School of Life Sciences, University of KwaZulu-Natal, Private Bag 
X01, Scottsville 3209, South Africa
        • 4Department of Anthropology, University of Colorado at Boulder, 
Boulder, CO 80309, USA
        • 5Institute of Zoology, Zoological Society of London, Regent's Park, 
London NW1 4RY, UK
        • ↵*Author for correspondence (dcodron@vetclinics.uzh.ch).
Abstract

Given the physiological limits to egg size, large-bodied non-avian dinosaurs 
experienced some of the most extreme shifts in size during postnatal ontogeny 
found in terrestrial vertebrate systems. In contrast, mammals—the other 
dominant vertebrate group since the Mesozoic—have less complex ontogenies. 
Here, we develop a model that quantifies the impact of size-specific 
interspecies competition on abundances of differently sized dinosaurs and 
mammals, taking into account the extended niche breadth realized during 
ontogeny among large oviparous species. Our model predicts low diversity at 
intermediate size classes (between approx. 1 and 1000 kg), consistent with 
observed diversity distributions of dinosaurs, and of Mesozoic land vertebrates 
in general. It also provides a mechanism—based on an understanding of different 
ecological and evolutionary constraints across vertebrate groups—that explains 
how mammals and birds, but not dinosaurs, were able to persist beyond the 
Cretaceous–Tertiary (K–T) boundary, and how post-K–T mammals were able to 
diversify into larger size categories.


On Apr 18, 2012, at 9:41 AM, Robert Schenck wrote:

> Fascinating article, like a few others here have commented, their
> hypothesis seems a little more sophisticated than it appears at first
> glance.
> 
> I would think that their model is what really needs to be examined in
> order to fully critique their idea. It sounds like they are saying
> that newly hatched large dinos are clearly in a different niche than
> their parents, and that they're competing with the smaller dinos.
> 
> But how is this going to drive them both to extinction? Usually (and I
> am not saying always) when two species compete, there ends up being a
> balance, OR one gets pushed out of the niche, and occasionally one of
> the competitors will go extinct. Normally a population biologist would
> address this by looking for morphological divergence as a result of
> niche competition. Often this type of divergence shows up as changes
> in feeding mechanism morphology.
> So do we see changes in the feeding morphology, the mouth-parts and
> head, of smaller dinosaurs co-incident with the spread of things like
> sauropods? I've never heard this before.
> 
> Rather, different sauropods have varied heads and mouth-parts,
> possibly suggesting that they were competing against each other (if
> they're derived from niche-competition in the first place, which would
> require positively demonstrating that such competition occurred
> between them).
> 
> Also, and I haven't read the article and we all know that
> news-articles are extremely poor sources of information, the Mesozoic
> is an astoundingly long period of time. What's true at the end of the
> Cretaceous was true throughout. Seems like the dinosaur radiation
> shouldn't've ever occurred if their hypothesis is correct.  They ran a
> computer model to, er, model this. My understanding is that population
> biology models, including the type that would look at competition,
> would be run on the span of generations or decades, not Eons.
> If their model shows dinosaurs crashing in after generations (or hell
> even after  a million years), then we know it's wrong, clearly they
> made it through this hurdle for millions and millions of years.
> These are all testable hypotheses that they're bringing up, should be
> interesting to see what happens.
> 
> Also, the authors, per the popular article anyway, say that the small
> dinosaurs became birds. But this is only true for one small set of
> dinosaurs, and many of the small dinosaurs in that set that didn't
> become birds didn't survive.
> 
> I think most people on this list, like myself, will notice that this
> idea of theirs sounds very much like the old way things were done in
> paleontology, that dinosaurs were inherently inferior, that they were
> doomed from the start to give way to more advanced mammals as only a
> matter of time (the idea that there are Grades of life). It sounds
> like that's really what they're saying, that Dinosaur biology utterly
> dooms them.
> 
> 
> On Wed, Apr 18, 2012 at 5:49 AM, Erik Boehm <erikboehm07@yahoo.com> wrote:
>> It seems to me the argument by the authors is more nuanced than their title 
>> suggests.
>> 
>> "Many species occupy one niche each; one species occupies many niches
>> In addition, new-born mammals occupy the same ecological niche as their 
>> parents: As they are fed with milk directly by the mother, they do not take 
>> any niche away from smaller species. With large dinosaurs, however, it was 
>> an entirely different story: They did not only occupy the adults’ one niche 
>> during their lifetime, but also had many of their own to pass through – from 
>> niches for animals with a body size of a few kilos and those for ten, 100 
>> and 1,000-kilo animals to those that were occupied by the fully grown forms 
>> of over 30,000 kilograms."
>> 
>> As others have pointed out, other egg laying reptiles did survive (egg 
>> laying mammals also survived), vivipatrious dinos did die out.
>> 
>> I think they are suggesting that the difference in size between offspring 
>> and adults requires different ecological niches for different stages of 
>> development in the same species.
>> Thus if one niche becomes untenable, the species dies out, and the other 
>> niches are left vacant.
>> Mammals generally care for their young until they are able to survive on 
>> their own in the same niche as the adults.
>> Birds seem to do this too - although mammals have seemingly more refined 
>> mammary glands for feeding infants, while birds have seemingly crude 
>> regurgitation of food.
>> 
>> In that system, if one niche becomes untenable, one species dies and the 
>> other niches remain filled by the birds/mammals occupying them.
>> 
>> If the parents are able to feed the young, I don't think egg laying factors 
>> into it. If the parents are not able to, then the limits of egg size 
>> exacerbate the difference in size between the offspring and the giant 
>> parents, making it more likely that the one species occupies different 
>> niches in its lifetime.
>> 
>> So I guess the hypothesis would be that parental feeding in dinos generally 
>> stopped before the young occupied the same ecological niche as their parents.
>> 
>> Perhaps the reliance on flight forc
>> and as a side effect forced birds to care for their young until the young 
>> occupied approximately the same niche as their parents?
>> 
>> So I guess the question is: how much evidence is there that adolescent 
>> dinosaurs occupied different niches from the mature adults in each of the 
>> major dino lineages?
>> The article/abstract just seems to assume they did due to size difference.
>> Do I recall correctly that there is evidence of age segregation in sauropod 
>> herds?
>> You might have a herd of fully mature adults protecting very young 
>> offspring, but then other herds composed entirely of adolescents of similar 
>> sizes?
>> 
>> 
>> 
>> --- On Tue, 4/17/12, Jura <pristichampsus@yahoo.com> wrote:
>> 
>> From: Jura <pristichampsus@yahoo.com>
>> Subject: Re: Dinosaur egg-laying contributed to extinction?
>> To: "Dinosaur Mailing List" <dinosaur@usc.edu>
>> Date: Tuesday, April 17, 2012, 7:22 PM
>> 
>> From: Jura <pristichampsus@yahoo.com>
>> To: "dinosaur@usc.edu" <dinosaur@usc.edu>
>> Sent: Tuesday, 17 April 2012 10:03 PM
>> Subject: Re: Dinosaur egg-laying contributed to extinction?
>> 
>> 
>> Another paper that seems to be out of touch with the actual inferred ecology 
>> of the Mesozoic (i.e., it once again assumes that the K/T event was the end 
>> of the dinosaurs, instead of the end of 75% of all life on Earth).
>> 
>> 
>> 
>> Also, no mention in the news story about how other reptiles were able to 
>> survive the K/T, or why viviparous plesiosaurs and mosasaurs bit the bullet.
>> 
>> 
>> Jason
>> 
>> 
>> http://reptilis.net
>> 
>> 
>> "I am impressed by the fact that we know less about many modern [reptile] 
>> types than we do of many fossil groups." - Alfred S. Romer
>> 
>> 
>> ________________________________
>>>> From: Ben Creisler <bcreisler@gmail.com>
>>>> To: dinosaur@usc.edu
>>>> Sent: Tuesday, 17 April 2012 9:44 PM
>>>> Subject: Dinosaur egg-laying contributed to extinction?
>>>> 
>>>> From: Ben Creisler
>>>> bscreisler@gmail.com
>>>> 
>>>> 
>>>> A news release from the University of Zurich. The paper in Biology
>>>> Letters has not been posted yet on the website.
>>>> 
>>>> Egg-laying beginning of the end for dinosaurs
>>>> 
>>>> http://www.mediadesk.uzh.ch/articles/2012
>> torben_en.html
>>>> 
>>>> 
>>>> Biology Letters website:
>>>> http://rsbl.royalsocietypublishing.org/content/early/recent
>>>> 
>>>> 
>>>> 
>>> 
>>> 
>> 
> 
> 
> 
> -- 
> Robert J. Schenck
> Kingsborough Community College
> Physical Sciences Department
> S332 ph# 718-368-5792
> Follow Me on Twitter: @Schenck
> KCC Class Schedule on Google Calendar: http://tinyurl.com/mqwlcy
>