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Re: David Hone on the Cope's Rule paper




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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