Re: =?unknown?q?Cope=92s?= Rule in the Pterosauria - Hone & Benton 2007

[Tim Williams <twilliams_alpha@hotmail.com>]

Mike Taylor wrote:

>                 I rather think the purpose of Hone and Benton's serier of 
> papers is to
> _investigate_ whether Cope's rule works in clades, using, y'know,
> _evidence_ and stuff.

I found this paragraph interesting (from the end of the Discussion)...

"Why were the small pterosaurs lost? It has been suggested (e.g. Unwin, 
1987; Penny & Phillips,
2004) that the steady loss of smaller pterosaurs maps neatly on to the 
appearance of birds through the Cretaceous. Slack et al. (2006) indicate 
this, although they urge caution about making a simple link from matching 
events to an assumption of competitive exclusion. Diet suggests that caution 
is warranted: most Cretaceous birds were insect-eaters, with some flightless 
fish-eaters and shorebirds in the Late Cretaceous, whereas insectivorous 
pterosaurs are known only from the Late Jurassic and Early Cretaceous, and 
most later ones were probably coastal fish-eaters. Further, there was always 
a substantial size gap between the largest birds and the smallest birds at 
any time. The suggestion that birds somehow drove the pterosaurs towards 
large size, and perhaps to final extinction, is currently not supported."

Were most Cretaceous birds really "insect-eaters".  I'm not saying the 
authors are wrong on this point, but I'm not sure what source(s) they are 
citing for this claim.  It was my impression that most of the Cretaceous 
euornitheans (ornithuromorphs) were aquatic or marine: _Yanornis_, 
_Yixianornis_, _Gansus_, _Hongshanornis_, _Archaeorhynchus_, _Ichthyornis_, 
Hesperornithiformes.  Most of these might have fed on fish (this is certain 
for _Yanornis_, based on stomach contents), though _Archaeorhynchus_ might 
have been more like a spoonbill in behaviour.

Also, it's known that confuciusornithids included fish in their diet.  Among 
enantiornitheans, there's AFAIK there's no evidence of insect-eating.  
_Longipteryx_ might have been a fish-eater, based on the shape of the bill; 
_Longirostravis_ was probably also an aquatic feeder (probing), also based 
on bill morphology; _Eoalulavis_ had crustaceans in its stomach; and 
_Jeholornis_ had seeds in its stomach.  _Nanantius_ might have been a marine 
bird, based on the discovery of a _Nanantius_ tibiotarsus in the gut of an 
ichthyosaur.

I can't think of a solitary Mesozoic bird for which there is direct or 
compelling evidence of insectivory.    The closest I've found is Zhou and 
Zhang (2007; "Mesozoic birds of China - a synoptic review") who write:

"None of the enantiornithine birds from the Early Cretaceous of China has 
preserved direct evidence of their diet. Our conclusion of their diet is 
currently inferred from their morphology and the environment they presumably 
inhabited. Since most of these small sized birds are equipped with 
well?developed conical teeth and arboreal in habit, it is likely they were 
mainly insectivorous or omnivorous."

Of course, it would make sense if many Mesozoic birds fed on insects (if not 
exclusively, but as part of their diet), beginning with _Archaeopteryx_.  
But that's different to saying that we have evidence of insect-eating in 
Mesozoic birds.

Comments anyone?

Cheers

Tim

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