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Re: New refs





"Brian Lauret" <zthemanvirus@hotmail.com> wrote:

Considering "hysilophodontids" were the ancestral Iguanodontoids it seems rather strange they were endotherms while their descendants,hadrosaurs,weren't.


Perhaps not so strange. It helps if you avoid thinking of "endothermy" and "ectothermy" as polar opposites, and think of them as two ends of the same spectrum. Among modern mammals, small mammals can be regarded as "more" endothermic than big mammals, since their high surface area to volume ratios renders them more prone to loss of body heat. Also, some fishes (tuna, some sharks) show a degree of endothermy.

In the course of dinosaurian evolution, individual lineages may have slid across the endothermic-ectothermic spectrum, depending on many factors: body size, required activity levels, diet, climate etc. The small size and cursorial habits of hypsilophodontids may have favored a greater emphasis on endothermy than their bulkier relatives (e.g. hadrosaurs), who could rely more on their sheer body mass to retain heat.



Tim

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