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prosauropod growth & metabolics



That at least some prosauropods experienced reptilian growth as demonstrated 
by Sander & Klein in Nature is not surprising. Basal dinosaurs - prosauropods 
and pretridactyl theropods as well as protodinosaurs - retained small ilia 
that were incapable of anchoring the very large thigh muscles present on more 
derived dinosaurs, including birds, as well as mammals with large ilial plates 
(this is discussed in DA etc). The modest leg muscles of basal dinosaurs 
indicates they lacked the high aerobic exercise capacity typical of birds and 
most 
mammals. On the other hand their long, erect legs and the presence of 
nonreptilian growth in some basal theropods and prosauropods indicates that 
their 
energetics were not entirely reptilian either, probably being more aerobically 
capable than any modern reptile. Instead brevischian dinosaurs appear to have 
possessed an intermediate metabolic/growth system that went extinct in the 
early 
Jurassic as the more advanced, bigger hipped longoschian dinosaurs became more 
energetic and bird/mammal-like. 

What is interesting about the S&K paper is how they use the terms ecto and 
endotherm. When they suggest that Plateosaurus was an ectotherm is seems 
doubtful that they really mean it was largely dependent upon external heat as 
the 
word actually means. Instead they appear to be denying that it had the well 
developed thermorgulatory system present in birds and mammals, which is 
probably 
correct but in no way means that the first dinosaurs were ectotherms. Indeed 
S&K 
soon say that plateosaurs were at the initial stage of endothermy, which is 
likely correct in that they were probably generating most body heat internally. 
Meanwhile, Feduccia in a commentary on the new, advanced Early Cretaceous 
wading bird from China says it was an endotherm, implying that it was a fully 
avian endotherm, even though more basal birds almost certainly were endotherms 
that made most of their body heat internally even if they lacked the entire 
avian suite of thermorgulatory adaptations. 

The need for an overhaul of the energetic physiological terminology is 
reinforced. 

G Paul