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Warm vs. cold dinos



Hi, girls and boys! It looks like we have a good discussion about dinosaurs out
 there. Great! Like someone said, in this topic nobody is a professional, so ev
erybody can give his/her opinion. So, come on!
First, Neil Clark ask me for the reference on cold-blooded mesozoic birds. This
 is: Chinsamy, A.; Chiappe, L.M. & Dodson, P. (1994). Growth rings in Mesozoic
birds. Nature, 368: 196-197.
I think it is best give it here, Clark, because someone else can be interested
on it. One question: if mesozoic birds were cold-blooded, is it easier to think
that the dinosaurs were also cold-blooded? or the birds lost the homeothermy an
d they obtain it later again?
Neil also asked for some references about polar dinos. One of the best (I can g
ive you some others, if you want them) is:Brouwers, E.M.; Clemens, W.A.; Spicer
, R.A.; Ager, T.A.; Carter, L.D. & Sliter, W.V. (1987). Dinosaurs on the North
Slope, Alaska: High Latitude, Latest Cretaceous Environments. Science, 237:
1608-1610.
They said that: "Preliminary stimates based on megaflore suggest that the Maest
richtian North Slope was characterized by annyal temperatures that ranged from
a warmest month mean of 10 to 12C to a coldest month mean of 2 to 4C. The o
currence of frost was therefore likely, but periods of weeks or months of subfr
eezing conditions are doubful". Also: "Estimates of paleolatitude for this area
during the Cretaceous time are as much as 15 farther north than present, rangi
ng from 70 to 85 N, on the basis of paleomagnitec data and tectonic reconstru
ctions, suggesting that the dinosaurs and associated organisms lived as much as
 18 north of the Maestrichtian Arctic Circle. Weeks, or more probably months,
of total darkness occurred on a seasonal basis at these latitudes".
So, you have several kinds of dinos living north the Arctic Circle, with period
s of darkness and freezing. Nowadays, there is a limit to the distribution of t
he reptiles situated south to the Arctic Circle (hundred miles south from it).
But the dinosaurs (nearly every kind) have growth rings in their bones, and thi
s imply cold-blooded. So, is it possible some kind of metabolism intermediate b
etween that of the mammals and that of the reptiles? This would explain nearly
every questin on this matter.
Some people say that the big size of the sauropods would be a problem if they w
ere endotherms, because overheating. But there are some mammals (are there any
ectotherm mammal?) really big, like some fossil rhinos weighting about 20 tons.
If this rhinos can be endotherms, why can't the sauropods be the same?
Jennifer asked about the kinds of warm and cold-bloodness. Easily, there are tw
o factors to consider: the capability to mantain the temperature, and the capab
ility to make metabolic heat. If you can mantain constant your temperature, you
are homeotherm. If you can't, you are poichilitherm (I don't know if this is co
rectly writen; if it isn't, please, excuse me). If you make a great ammount of
internal heat, you are endotherm. If you don't make it, you are exotherm.
So, you can be a endotherm homeotherm, like the mammals. You can also be a exot
herm poichilotherm, like the reptiles and insects. And you can be a exotherm ho
meotherm, like the leatherback turtles, the big crocs, the big sharks and tunas
, etc... There are no known endotherm poichilotherms (it is impossible). Maybe
the dinosaurs were included in the exotherm homeotherm group. Or maybe not.
And, finally, the ancestral dinosaur, the "mother of all dinosaurs" was surely
bipedal, like its ancestors the "protodinosaurs" and most of the known primitiv
e dinosaurs.
Excuse me for the loooooong post.
Cheers, Nino.

P.S.: Nice idea that of the surface area of the sauropods, Paul.

Bernardino P. Perez-Moreno
Unidad de Paleontologia
Departamento de Biologia
Facultad de Ciencias
Universidad Autonoma de Madrid
28049 - Madrid
SPAIN