Re: Evolution:Small Scale/Grand Scale

[Tom Holtz <tholtz@geochange.er.usgs.gov>]

>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."

These distinctions are what are somewhat like the differences between
microevolution and macroevolution, although many would included
species-to-species evolution within macro.  Much of evolutionary debate
over the past decades has been whether microevo and macroevo are different
phenomena, or just differences of scale.

>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?

Under a "gradistic" system, you would be correct. But, as a few of you may
have noticed (;-)), I follow a cladistic taxonomy, in which names do not
describe evolutionary grades (similar levels of development), but clades
(an ancestor and all of that ancestor's descendants).  Since birds descend
from the common ancestor of all dinosaurs, and dinosaurs descend from the
common ancestor of all reptiles, than cladistically, birds are dinosaurs
(i.e., members of the clade Dinosauria) and dinosaurs are reptiles (i.e.,
members of the clade Reptilia).

Hope that clears up what I was talking about.

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.