Skeptic Tank Text Archive File

Organization: animal -- coelomate -- deuterostome
From: colby@bu-bio.bu.edu (Chris Colby)
Message-ID: <110991@bu.edu>
Followup-To: talk.origins
Newsgroups: talk.religion.misc,talk.origins

In article <1993Feb23.203501.3730@prpa.philips.com> ross@prpa.philips.com 
(Ross Morley) writes:

>Well I, for one, would like some rational explanation of why this
>theory can't be true. Your response to this reasonably phrased and
>seemlingly plausible theory does not engender any respect for your
>view nor do anything at all to refute the theory.

Read the newsgroup talk.origins for awhile. I've set follow-ups
to that group, BTW.

>So what *is* the difference between dinosuars and present day 
>reptiles, apart from size?

It's a matter of lineage. All reptiles share a common ancestor.
Dinosaurs share a common ancestor that descended from the
reptilian common ancestor -- only species in lineages descended
from the dino-ancestor are called dinosaurs. (By this criteria,
birds can be classified as dinosaurs, BTW.) Living reptiles
are from a different lineage and can never be called dinosaurs.

Incidentally, bigness is not necessarily a dinosaur feature -- 
there were plenty of small and average-size dinosaurs as well.
Read "The Dinosaur Heresies" by Robert Bakker for a good, popular
account of what is currently known about these animals. Recently
(past 20 years or so), new evidence has forced paleontologists to
rethink their views on dinosaurs. Bakker argues forcefully that
dinosaurs were vigorous, warm-blooded animals, not dull,
lumbering giants as they were previosly depicted. A very enjoyable
book.

Here's a phylogeny of the reptiles, in case you are curious.
                                        
                                        (extinct)       (extinct)
turtles mammals       lizards snakes  crocs    s-dinos  birds o-dinos
  *        *       *      *       *          *     *      *
   *        *          *            *           *        *
    *        *           *             *           *  *
      *        *           *             *          *
        *        *           *              *    *
          *        *           *              *
            *        *            *       *
              *        *             **
                *         *       *
                   *         **
                      *   *
                        *
                        *
                  ancestral reptile

"S-dinos" means saurishcian dinosaurs and "o-dinos" ornithiscian
dinosaurs. Birds are the only living dinosaurs left (barring a
surprize relic population somewhere -- very unlikely). Of course,
most biologists call them "birds" not "dinosaurs" to emphasize
their unique qualities. There are three main lineages of reptiles
anapsids (turtles), diapsids (all the other groups in my cladogram
except mammals) and synapsids (mammals). Like birds, most biologists
call them by a unique name ("mammals") to stress the differences.
This leaves the group of species what we do call reptiles without
some of the lineages that "should" (if relationship were the only
criteria) be included. In bio-speak, reptiles are a para-phyletic 
group.

The information for the phylogeny came from a variety of sources.
The best being "Vertebrate Palaeontology" by Michael J. Benton.

P.S. Since this is crossposted to t.r.m I could mention that I
generally post to talk.origins and have written a file that
explains evolutionary biology. Evolution is misunderstood by
almost everyone. Mistakes such as saying that humans evolved
from living apes or organisms do things for the good of their 
species or behave in a way to propagate their species are common
misconceptions that are presented (often as fact) in TV nature
shows and popular magazines. 

Furthermore, evolution is often
represented as progress and the idea that one can construct an
"evolutionary scale" going from "lower" to "higher" animals is
a popular misconception most people have. These are serious
mistakes, and the file I have written attempts to explain modern
evolutionary biology and dispel these common misunderstandings.
In addition a summary of the evidence supporting evolution is
presented.

If you would like a copy, email me at the address given in my
.sig and I'll send you a copy. The file is about 20 pages in
length and written (hopefully) so someone with little background
in science or biology can understand it.

>Ross Morley                   .---.     email:  ross@prpa.philips.com

Chris Colby   ---      email: colby@bu-bio.bu.edu     ---