Re: David Hone on the Cope's Rule paper

[Tim Williams <twilliams_alpha@hotmail.com>]

Mike Keesey wrote:

> You certainly can say that without contradicting David Hone, since in an 
> earlier paper he reached a similar conclusion: "Only the Cretaceous 
> sauropods [among large dinosaurs] do not follow the trend, and these are 
> characterized by their extreme variance of sizes" (Hone et al. 2005:594).
>
> Hone, D. W. E., T. M. Keesey, D. Pisani & A. Purvis. 2005. 
> Macroevolutionary trends in the Dinosauria: Cope's rule. Journal of 
> Evolutionary Biology 18:587-595.

The thing is that the "Jablonski polygons" used to illustrate this point 
actually separate the Cretaceous sauropods from the Jurassic sauropods.  But 
all Cretaceous sauropod lineages are known from the Jurassic (diplodocoids, 
brachiosaurids, titanosaurs), and the ancestor-descendent pairings (which 
were also used to test Cope's Rule) do cross the Jurassic-Cretaceous 
boundary.  So I'm not entirely sure why the Jablonski plot separated 
Jurassic and Cretaceous sauropods - especially if the objective was to test 
Cope's Rule over the entire evolution of the Sauropoda.  If you combine the 
plots (Jurassic+Cretaceous) into a single shape, most of the Late Jurassic 
sauropods would fall outside the polygon, making them outliers.

Thus, when Hone et al. (2005) says "Only the Cretaceous sauropods do not 
follow the trend", I guess I would extend this to the entire Sauropoda; if 
the Cretaceous sauropods don't get bigger, then Cope's Rule does not hold 
for the clade as a whole.  That's why I quoted Carrano over Hone &c.

Cheers

Tim

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