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




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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