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Cyclical growth leaves marks in bone tissue that are in the forefront of discussions about physiologies of extinct vertebrates



My apologies.  I did not change the title of the message


On 7/18/12 1:06 PM, "Clair Ossian" <clastic@verizon.net> wrote:

> Just appeared in tomorrow's Nature Magazine.
> 
> Clair Russell Ossian, Ph.D.
> Professor Emeritus, Geology
> Tarrant County College
> 2805 Raintree Drive
> Carrollton, TX 75006
> 
> Seasonal bone growth and physiology in endotherms shed light on dinosaur
> physiology
> 
> 
> Meike Köhler,  Nekane Marín-Moratalla, Xavier Jordana  & Ronny Aanes
> 
> ABSTRACT:
> Cyclical growth leaves marks in bone tissue that are in the forefront of
> discussions about physiologies of extinct vertebrates1
> <http://www.nature.com/nature/journal/v487/n7407/full/nature11264.html#ref1>
> . Ectotherms show pronounced annual cycles of growth arrest that correlate
> with a decrease in body temperature and metabolic rate; endotherms are
> assumed to grow continuously until they attain maturity because of their
> constant high body temperature and sustained metabolic rate. This apparent
> dichotomy has driven the argument that zonal bone denotes ectotherm-like
> physiologies, thus fuelling the controversy on dinosaur thermophysiology and
> the evolution of endothermy in birds and mammal-like reptiles. Here we show,
> from a comprehensive global study of wild ruminants from tropical to polar
> environments, that cyclical growth is a universal trait of homoeothermic
> endotherms. Growth is arrested during the unfavourable season concurrently
> with decreases in body temperature, metabolic rate and bone-growth-mediating
> plasma insulin-like growth factor-1 levels, forming part of a plesiomorphic
> thermometabolic strategy for energy conservation. Conversely, bouts of
> intense tissue growth coincide with peak metabolic rates and correlated
> hormonal changes at the beginning of the favourable season, indicating an
> increased efficiency in acquiring and using seasonal resources. Our study
> supplies the strongest evidence so far that homeothermic endotherms arrest
> growth seasonally, which precludes the use of lines of arrested growth as an
> argument in support of ectothermy. However, high growth rates are a
> distinctive trait of mammals, suggesting the capacity for endogenous heat
> generation. The ruminant annual cycle provides an extant model on which to
> base inferences regarding the thermophysiology of dinosaurs and other
> extinct taxa.
> 
> http://www.nature.com/nature/journal/v487/n7407/full/nature11264.html