Evolution:Small Scale/Grand Scale

[Amado Narvaez <anarvaez@umd5.umd.edu>]

On Thu, 18 May 1995, Tom Holtz wrote:
> Well, this expert, and many others, agree that dinosaurs ARE reptiles (and
> birds ARE dinosaurs), and no member of Reptilia (aka Sauropsida, sort of)
> has fleshy external ears.  [But, yes, among the reptiles, birds are the
> closest comparison].

In the latest issue of the new magazine "Dinosaurus," Mark Norell talks 
about the new layout of the AMNH, pointing out that rather than 
displaying the dinosaurs exclusively by time period, they are separated 
into saurischians and ornithischians. He is later quoted as saying, 
"Birds and theropod dinosaurs are closer to Tyrannosaurus than the 
Tyrannosaurus is to ornithischian dinosaurs."

Do I recall correctly that some paleontologists think that saurischians 
were more likely to be warm-blooded than ornithischians were? If that's 
the case (saurischians=warm-blooded; ornithischians=cold-blooded), why 
should these two dramatically different orders be lumped together at all? I 
would think that the attribute of warm-bloodedness is almost as great a 
milestone in the history of evolution as giving birth to live young.

I have this image of evolution on two scales. On the small scale, one 
species evolves into another. On the grand scale, one phylum evolves into 
another. The first fish that crawled out of the sea to inhabit the land 
evolved on a small scale from a lungfish, but on a grander scale it 
marked a change from one phylum (fish) to another (amphibian)--kind of a 
"one small step for a fish, one giant leap for vertebrates."


But getting back to Dr. Holtz's comment (and I apologize for getting away 
from it, but I couldn't think of a succinct way of expressing my 
thoughts)--if _most_ reptiles are cold-blooded, don't the warm-blooded 
ones (dinosaurs and birds) deserve a declaration of independence in the form 
of a new phylum?

----- Amado Narvaez
      anarvaez@umd5.umd.edu