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Re: The iguanodont paper



On Dec 9, 2007 7:49 PM,  <GSP1954@aol.com> wrote:
>
> The above arguments can be flipped to show why they are simplistic. For
> example, it remain extraordinary that among all the dinosaur groups only one, 
> the
> flying birds, have developed marine forms,

Actually, marine forms are limited to a subclade of _Euornithes_.

> unlike mammals which have spawned a series of marine forms from nonflying 
> types.

Again too broad. Marine forms are limited to _Placentalia_. (Although
aquatic forms are dispersed much more broadly, throughout
_Mammaliaformes_ at least.)

But in both of these cases, we pinpoint the presence of the character
using clades. It doesn't really do us much good here to erect a name
for non-euornithean pan-Aves or non-mammaliaform pan-Mammalia.

> This important truth is obscured
> by the silly notion that saying that just because one group of dinosaurs
> evolved marine forms that this is typical of the entire clade.

Agreed, and I think people should be conscientious to pick the least
inclusive clade in such cases. But, at the same time, it is silly to
say there's no such thing as a marine dinosaur.

> In any case the old
> exclusion of birds from Dinosauria was not a taxonomic issue, but a
> phylogenetic one due to the mistaken consensus that birds evolved from early 
> archosaurs
> independently of theropods.

Depends on the author, but certainly true for many.

> Hadrosaurs were not a mere subset of iguanodonts. They had more complex
> dental batteries -- the most sophisticated among dinosaurs - a tendency to 
> develop
> nasal passage crests, modified ilia and the like.

Compare: "Bats are not a mere subset of placentals. They have more
complex inner ears -- the most sophisticated among placentals-- a
tendency to develop facial appendages to assist with echolocation,
modified hands and the like. "

Bats retain mammalian characters just as hadrosaurids retain
iguanodontian characters. Of course they have picked up new ones, but
that's true of most subclades. It does no disservice to the uniqueness
of a group to say that it is included within another group.

> Lumping them together is
> rather like lumping bison and cattle. Of course, we could call bison noncattle
> bovids. Or are cattle nonbison bovids? Is suppose will have to check a 
> cladogram
> and see.

I don't think that's a good parallel, since neither "bison" nor
"cattle" represent paraphyletic groups (at least not in the way I'm
thinking of them). Each represents a clade, and these clades actually
overlap. (I know, I've eaten some of that overlap.)

A better analogy would be this: creating a taxon, "Deeroidea", which
includes all ruminants except for bovoids (bovids and giraffids), and
then considering that as a group somehow comparable to _Bovoidea_.
What is the utility in lumping cervids with tragulids to the exclusion
of bovoids? Similarly, what is the utility of lumping _Ouranosaurus_
with _Camptosaurus_ to the exclusion of _Edmontosaurus_?
_Ouranosaurus_ shares millions of years of ancestry with
_Edmontosaurus_ that neither of them share with _Camptosaurus_.

-- 
T. Michael Keesey
Director of Technology
Exopolis, Inc.
2894 Rowena Avenue Ste. B
Los Angeles, California 90039
http://exopolis.com/
--
http://3lbmonkeybrain.blogspot.com/