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Hi, girls and boys!
Paul considered that T.rex was endothermic in his analysis about the diet of th
And talking about hot-blooded dinos, DaveH47 gave a good list of reasons to thi
nk that the non-avian dinosaurs were hot-blooded. I agree with him. I think the
y were endothermic (at least some of them). But, as he said, nearly every theor
y on hot-blooded dinos has some problems, and I want to tell you some of them,
in order to give so much information as possible.
-Upright gait: it is true that no cold-blooded animal is know with posses an up
right gait only. But some of the are capable to mantain this gait in short dist
ances (the crocodiles are capables of gallop!), and the gait of the dinosaur co
uld be an improve mode of this one.
-Predator-prey ratios: There is some problems with the predator-prey ratios in
fossil comunities. Some of them come from the fossilization process (only those
specimens that died in some special conditions became fossils, so you haven't
a exact record of that community), and some others from some fossil-sites. In t
he Ghost Ranch Quarry there are a 90% of predators (I don't know the exact numb
er, but it would be nearly of that one), the same in the Morrison Formation and
in some others. Why? No known community of hot-blooded animals present that ra
tios, but they are presented in some communities of cold-blooded predators (the
y become together to breed, for example). Only one is known in hot-blooded:the
Rancho La Brea fossil-site, and this is a tramp.
-Rapid evolution: yes, it is true that the hot-blooded genera changes faster th
an the cold-blooded ones. But some genera of dinos are present in the fossil re
cord during tens of millions of years, like _Iguanodon_ and some others. In nea
rly each group there is some genera that last tens of millions. Why?
-Pole-to-Pole: yes, the dinos lived in the polar zones, where at least the wint
er had freezing temperatures. This is one of the most solid arguments favourin
g the hot-blooded theory.
-Growth rings: there are many problems with this argument. The type of bone tha
t the dinosaurs have only say that they growth fast after the birth and during
the firts years of life. This same kind of bone is present in crocodiles and ot
her cold-blooded animals. The kind of bone of the hot-blooded animals is slight
ly different. Luis Chiappe make and analysis of the bone of some Mesozoic birds
and he said that they were cold-blooded. So the birds developed the hot-blood
after the Mesozoic. I can give you the reference if you want it.
-Therapsids: the main advantage of the dinos on the therapsids was the locomoto
ry aparathus, not the endothermy. The therapsids were sprawling, so the upright
gait of the dinos was a good advantage on locomotion, and this made the dinos
a very good predators.
Nevertheless, I think they were hot-blooded, although there is no one perfect a
rgument on favour of this.
Bernardino P. Perez-Moreno
Unidad de Paleontologia
Departamento de Biologia
Facultad de Ciencias
Universidad Autonoma de Madrid
28049 - Madrid