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Re: Hot-blooded dinos



Nino wrote:-

> I agree with him [DaveH]. I think they were endothermic

Me too.

> -Upright gait: 
I seem to remember a lizard that can run for some distance on it's 
hind feet.

> -Predator-prey ratios: In the 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. 
I suppose if you happen to uncover a group of fossil baboons, or even lions, in
their living quarters, you would get a very high value of the 
predator:prey ratio. Even if you have a death assemblage in situ, you 
will not be dealing with a living community when dealing with animals 
that could travel great distances.  You would probably have to 
uncover a single stratigraphical level the size of the Serengeti to have 
anything close to a reliable community structure for dinosaurs.

> -Rapid evolution: But some genera of dinos are present in the fossil re
> cord during tens of millions of years, like _Iguanodon_ and some others.
In terms of species though, I don't think they lasted quite so long.  
....but then we move into a discussion on what a fossil species 
represents i.e. does it represent a true species?

> -Pole-to-Pole: yes, the dinos lived in the polar zones, where at least the 
> wint
> er had  freezing temperatures. 
Did the winters have freezing temperatures?  Is it not possible that 
warm air currents kept the polar regions warm?  I'm sorry but I 
haven't read any evidence that shows freeze-thaw occurred in polar 
regions when dinosaurs were alive.  I would like to know of any 
publication that shows what polar temperatures were at this time.

> -Growth rings:
One dinosaur bone I have been looking into has 'growth rings' 
superficially, but not when you look at it closely.  The rings are 
purely a taphonomic feature produced by the deseccation of the bone 
and shrinkage of the compact bone relating to secondary 
phosphatisation (perhaps).  I need to find out more on the secondary 
taphonomic processes involved with the preservation of boney 
material.

It seems difficult to resolve the problem of 'which came first: 
bipedalism or quadrapedalism?'.  Perhaps evolution works in cycles 
(as many have suggested before) and we shouldn't talk in terms of 
characteristics evolving more than once, or being secondarily 
derived.  This may also apply to the endothermy as well, especially 
if we think that dinosaurs (at least some) were endotherms and, as 
Nino pointed out, that there is evidence that early birds were 
cold-blooded.  Is this a circular argument? ;-)

Neil