Re: Dinosaur egg-laying contributed to extinction?

[Robert Schenck <schenck.rob@gmail.com>]

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