[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: The iguanodont paper



"Tim Williams" <twilliams_alpha@hotmail.com> wrote:

> This is not what I meant at all.  I was only stating
 > that it was evolution itself that derived birds
from  > dinosaurs.  That's all.  The methodology by
which we  > discern this evolutionary history might be
considered > "reform" (i.e., cladistics), but the
history itself   > can't change.  From that
perspective, it is entirely  > appropriate to say that
the idea that birds are not   > dinosaurs was indeed
"never true". This is a separate > issue from what we
consider(ed) a "dinosaur" in the   > vernacular sense,
since the latter might include      > plesiosaurs,
_Dimetrodon_ and even woolly mammoths.   > It's the
job of science to correct misconceptions, not >
perpetuate them simply because they were once widely 
> disseminated - or even canonical.

And dinoboygraphics@aol.com wrote:

> Sorry, I don't believe that's correct Mike.  Birds
did > not evolve from dinosaurs in the 1970s, they did
it in > the Jurassic.  Just because paleontolgoists in
the    > 1930's did not think it was true doesn't
change the   > fact that there have been aquatic
dinosaurs.  Now, I  > realize that the strict emphasis
on phylogenetic      > definitions is more recent, but
(ironically) I don't   > think you are giving our
predecessors enough credit.  > Romer, Brown, etc. were
clearly intending "dinosaurs" > to be one (or
two...Saurischia and Ornithischia       > separately)
monophyletic groups.  When they indicate  > that there
weren't aquatic dinosaurs (possible        > excepting
sauropods in those days) they didn't mean   > "not
counting birds because we like to use            >
paraphyletic groups".  They actually believed that   
> dinosaurs were a dead end, and both popular and     
 > technical literature is rife with statements to
that  > effect.  Those statemetns were factually
wrong, and   > you can't pretend that their statements
were somehow  > not wrong just because we place a
higher premium on   > monophyly in our taxonomy.

++++++++++++++++++++++++++++++++++++++++++++

Actually, I think that you guys might be arguing a
completely different point from Mike's. Mike is right
in that many of the statements said in the past about
dinosaurs, were correct at the time. P.N. just
hijacked useful "paraphyletic" terms and redefined
them to fit into a monophyletic view. That birds
weren't accepted at descendants of dinosaurs yet, has
little to do with anything. We are talking about
classification here; a system designed to make
understanding the diversity of life easier for a human
brain to deal with. 

Scott- I disagree with your assessment of Romer et al.
Had birds been accepted as descendants of dinosaurs,
the definition of Dinosauria would not have changed at
all. The only difference would be a retraction of the
statement that dinosaurs were an evolutionary dead
end.

Don't believe me, then go through Romer's Osteology of
the Reptiles again. Romer, and every paleontologist at
the time knew that mammals evolved from therapsids,
which evolved from pelycosaurs (or eupelycosaurs for
those feeling an urge to be pedantic), and so on. Yet,
despite this knowledge, Romer maintains a clear
dividing line between even the most mammal-like
cynodonts, and true mammals (which are not featured in
the book). This separation is maintained for other
groups in that book too. Even though the thought of
birds evolving from dinosaurs was a contentious one at
the time, there was little doubt that birds evolved
from reptiles at some point in time. Yet birds are not
covered at all in the book. Better yet, look at snakes
and lizards. Any systematists worth his salt could
tell you that snakes evolved from lizards. Even when
evolution was still in its infancy, this was pretty
darned obvious. Yet, again, despite this, there is not
a non-lacertilian ophidian to be found in the tome.
There are plenty of talks about what lizard, snakes
evolved from, but the separation of the two is always
maintained.

Which is to say nothing for the fact that we have over
150 years of paraphyletic groups being used just fine
without interfering with the knowledge that all life
shares a common ancestry. 

So yeah, contra your statement, I would say that Romer
did mean to say: "yeah we like paraphyletic groups." I
would only add to it: ...because they just make things
easier to understand.

Jason

"I am impressed by the fact that we know less about many modern [reptile] types 
than we do of many fossil groups." - Alfred S. Romer


      
____________________________________________________________________________________
Looking for last minute shopping deals?  
Find them fast with Yahoo! Search.  
http://tools.search.yahoo.com/newsearch/category.php?category=shopping