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Re: Warm/Cool/Cold blood



>       One of the things that bothers me about the warm/cool/cold blood
>arguments relates to the theory that nature does not like to invent the
>same idea twice. 
>
>       Baker's argument that dinos and birds are related, and that warm
>bloodedness was in their common ancestor leaves one gaping hole to me. No
>"family tree" I have even seen left any doubt that early mammals existed
>before the dino/bird branch broke off the reptile. 

Exactly.  In fact, one of the observations to come out of the Hot/Cold
debate was the fact that the biomechinisms of Mammalian and Avian endothermy
are not the same.  In fact, there are also warm-blooded moths, tuna, broding
pythons, and a "warm-blooded" skunk cabbage.  The cellular mechanisms for
achieving warm-bloodedness are different in all these cases.

>       Does this mean that warm bloodedness arose at least twice, Once
>for the dino/bird and once for mammals. Or does it mean the theory is
>correct and that dino/bird/mammals broke off of the reptile branch in
>some, as yet, unknown way?

There is one scientist, Gardiner, who thinks that birds, mammals, and
dinosaurs (&pterosaurs) had a common ancestor not shared with lizards,
crocs, or turtles.  However, his ideas can be shown to be false when fossil
synapsids and other fossil groups are added to his matrix.

>       Personally I think that some ancestor of the dinosaurs, birds and
>early mammals evolved "cool" bloodedness. Then the various branches
>evolved this in various ways, and to various degrees of "warm". This means
>that the dino/bird/mammal ancestor broke off earlier then we normally
>believe. But considering how "holey" the fossil record is this is very
>possible. 

Actually, there are many features of the skeleton which show that mammals,
therapsids, and pelycosaurs (the last two are the so-called "mammal-like
reptiles") on the one hand and all other amniotes (terrestrial,
hard-shelled-egg laying vertebrates) on the other diverged very early in the
fossil record.  The fossil record isn't that "holey" with regards to
mammalian origin - its one of the strongest pieces of evidence of vertebrate
evolution.

>
>Ralph Lindberg email=>dragonsl@hebron.connected.com
>more hobbies then time
>
>

Thomas R. HOLTZ
Vertebrate Paleontologist, Dept. of Geology
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Phone:301-405-4084