RE: David Hone on the Cope's Rule paper

[Tim Williams <twilliams_alpha@hotmail.com>]

David Hone (via Mike Taylor) wrote:

> There is good evidence for the positive benefits of large size and for 
> increase in sizes across lineages. This may often (see dinosaurs) be 
> represented by a diversification event, rather than an
> active trend for large size (see pterosaurs), but it is there. CR is alive 
> and well, and should not be dismissed until tested fully. So far it has 
> been, at best, tested badly in a few lineages (look at the
> effects of different levels in Pterosaurs, but also see Alroy, 2000) so to 
> say that I'm wasting my time seems to me (obviously) to be very well wide 
> of the mark.

Without contradicting what David said, I would point out that sauropods (the 
'biggest of the big') do not appear to follow Cope's Rule.  Quite the 
opposite, in fact.  The most recent study (that of Carrano, 2005) 
demonstrated a trend of decreasing body size among Sauropoda in the later 
Cretaceous period.  This was largely due to the proliferation to certain 
'undersized' titanosaurs in the Late Cretaceous, especially the 
Saltasaurinae.

While it is true that the majority of sauropod lineages did indeed attain 
gigantic body mass throughout their evolution, these same lineages ended 
with a sputter, not a bang.  As Carrano put it, "...smaller sauropods tend 
to be the end points of their respective lineages."  Certainly, there were 
some massive sauropods in the later Cretaceous period (_Pelligrinisaurus_, 
_Puertasaurus_, &c among titanosaurs).  But there were massive sauropods 
throughout the entire post-Triassic Mesozoic, including some behemoths as 
far back as the Middle Jurassic (Charroud and Fedan, 1992).

> *However*, the bulk of the literature deals with the assumption that most 
> pterosaurs were piscivorous, and without good evidence published to the 
> contrary, that is what I am going on, and what I will refer to. Still, if 
> nothing else, the vast majority of pterosaurs are at least known from 
> marine / lacustrine environments and while that is not exactly compelling 
> evidence for dietary preference, it is at least good circumstantial 
> evidence.

The same is largely true for Mesozoic birds.  Yet, it has been argued that 
the majority of Mesozoic birds were arboreal insect-eaters.

Cheers

Tim

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