Re: What the fossil record tells us about trends in pterosaur diversity

[Mike Habib <habib@jhmi.edu>]

David Peters wrote:

> As in anything dealing with fractals, it depends entirely on your  
> scale.

Technically, fractal shape is scale-independent (by definition), but  
understand your point (which appears to be about resolution).

> If you can divide the Triassic, Jurassic and Cretaceous each into  
> three for a total of nine units, then the answers are pretty clear -  
> with some allowance for an occasional Lazarus taxon (which has _not_  
> popped up yet). If you want to get more specific, then it gets  
> trickier. From this vantage point ~65my after the last of the  
> pterosaurs, I wouldn't get more specific on scale.

Sacrificing resolution in exchange for macropattern analysis can work  
to a degree, but a nine-slice analysis of the entire Mesozoic is so  
coarse that I would be very conservative about most of the resulting  
conclusions.  At that scale, the best you can really say for  
pterosaurs is that there is a pterodactyloid origin and radiation in  
there somewhere, that the origin of Pterosauria is probably in the  
Triassic somewhere, and that the end-Cretaceous seems to be the  
extinction point.  Your confidence intervals will be enormously wide  
for any analysis using only nine intervals, so saying much more is  
very difficult.  You might be able to say more for the start and  
finish of a few specific lineages that have better records, presuming  
that taphonomic bias is consistent for the clade in question.

> The most interesting thing about current German and Chinese  
> Lagerstatte is for whatever reason, they seem to have preserved some  
> of the most interesting intervals in the fossil record where  
> everything was changing.

The problem here is that it will appear that way whenever you have a  
few good sites providing most of the material.  In other words,  
because the German and Chinese Lagerstatte provide most of our high- 
resolution information, they will appear to have preserved the  
transition intervals, essentially by definition.


Cheers,

--Mike


Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280-0181
habib@jhmi.edu