Re: Were dinosaur ecosystems continent-sized? (resend)

[Jonas Weselake-George <Paleo@ncf.ca>]

I don't quite buy that this is much different from the present day condition. 
However it is still a fascinating direction to take in research.

If one were to collect skeletons from all wolf species/sub-species would they 
look that different? The same goes to a lesser extent for larger taxonomic 
groups. What happens assuming a researcher who doesn't have extant terrestrial 
mammals to look at? 

If you throw in the preservation bias for mesozoic deposits, would it look that 
different from more recent pliestocene deposits? This despite the fact that 
there are actually three or four divisions/faunal regions of mammals across the 
North American continent.


The connection with climate is also a critical point. I recall that studies 
were showing larger ranges, across broader habitat types (less specialisation 
and niche segregation) and higher evolution rates among higher latitude 
animals. These features don't translate directly into patterns of biodiversity, 
but they are certainly related to it. If anyone is more up-to-date on the 
ecological literature, I'd love to hear their thoughts.


>From the ecosystem perspective smaller scale ecological conditions matter a 
>great deal. Everything is a patchwork of habitats within habitats: Well 
>drained islands in bogs and wet oases in deserts; Different conditions on the 
>north face of each hill compared to the south face - This is what allows 
>biodiversity and niche segregation to exist. It is the alpha diversity which 
>matters most.

Attempting to reconstruct ecological existence at smaller (but equally widely 
distributed) scales is important. It is also certainly extremely difficult 
given the preservation bias in ecosystems with entire categories of habitat 
having to be inferred from marginal evidence. We have no real idea of these 
structures despite the fact that they were undoubtedly different (perhaps 
universally different eg. with few angiosperms in interspecies interactions).


Did climatic conditions increase the level of alpha diversity by creating a 
world of adaptable generalists with low beta diversity? Did the peak of 
ecological (rather than morphological) diversity shift to work at a lower 
taxonomic level? Or is this primarily an artifact of slightly larger body sizes 
and correspondingly large ranges to achieve minimum breeding populations? Was 
intraspecies diversity clinal? What did the genome look like and the structure 
of gene flow? Are we mistaking the gross features of genus level morphology for 
the living ecological performance?

I guess my basic point is that "dinosaur populations spanned entire continents, 
often interbreeding across these ranges" is very different from saying that 
"entire continents consisted of a single ecosystem". The findings are 
fascinating, but we have to be careful what we conclude when we step into 
ecological conclusions.

Wonderful isn't it?

-Jonas Weselake-George

P.S. I haven't read the paper yet - this is my overexcited knee-jerk response 
to a press release.

P.P.S. The press release describes the climate as stable - I assume this is 
with regard to latitudinal gradients and not temporal variation at the annual 
or million year scales. With the very recent glaciation events excluded, I 
doubt the latter would be an easily defensible position.


On Thu, 22 Apr 2010 18:54:21 -0700
GUY LEAHY <xrciseguy@q.com> wrote:

> 
> Resent, this time in plain text... :-)
>  
> According to this analysis, yes:
>  
> http://www.mcgill.ca/newsroom/news/item/?item_id=116613
>  
>  http://www.pnas.org/content/early/2010/04/05/0913645107
>  
>  A couple of problems right off the top:
> 
> 1. No faunas from Utah, New Mexico or Texas are included in the dataset. 
> 2. The upper Maastrichtian Scollard fauna is not included, but the 
> lower-middle Maastrichtian Horseshoe Canyon fauna is...
>   
> It's an interesting coincidence in time this appears a few days after the 
> publication of a new pachycephalosaur (_Texacephale_), where the authors 
> suggest exactly the opposite scenario: 
> http://www.sciencedaily.com/releases/2010/04/100419132406.htm
>  
> Guy Leahy                                       


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