Re: smallest ANCIENT non-bird dinosaur - was what I was asking

["T. Michael Keesey" <keesey@gmail.com>]

On Sat, May 3, 2008 at 10:22 PM, Tim Williams
<twilliams_alpha@hotmail.com> wrote:
>
> And yet... that's exactly what the authors did when they named it "Pakicetus" 
> - the "Paki[stan] whale".
> (Ditto for _Ambulocetus_, _Artiocetus_, _Rodhocetus_, Himalayacetus_... and 
> so on.  All have "whale" names too.)

As Dann Pigdon pointed out, that means squat for taxonomy. (He beat me
to the _Basilosaurus_ example.) And anyway, so what? -- they are
stem-cetaceans, so why not have "-cetus" in the name? Juts don't put
it in _Cetacea_.

> Now you're cheating, Mike!  Get this thing off dry land, and put it in the 
> water.  Then we'll see how "whale-like" it really is!  :-)

Regardless of whether that genus was aquatic or not, the earliest
stem-whales were terrestrial. (Just like the earliest stem-bats were
nonvolant and the earliest stem-humans lacked human-sized brains.) So
the example holds. :)

> First of all, it implies that the term "bird" should be limited to the 
> crown-group, which I think is a big no-no.  (I know that's not the intention, 
> but I think we have to be careful in associating the word "bird" too closely 
> with the crown-group only.  I especially like Jeff Hecht's reasoning for why 
> this should be avoided.)

I'm fine with that.

>  Secondly, I'm not at all sure what maximization of either "safe inferences" 
> or "generalizations" regarding hypothetical ancestors have to do with clade 
> definitions.  Does this really matter?

Yes.

People (not just neontologists) are prone to making generalizations
about the stem group from characteristics of the crown group.
Sometimes this works out, but often it doesn't. Limiting popular names
which were *coined in neontological literature* to crown groups makes
it safer to make inferences about the ancestral character states of
the clades they signify.

I think it can also ease interdisciplinary communication. It's a lot
easier to assume that classic neontological names like _Insecta_,
_Pinaceae_, _Fungi_, _Gastropoda_, etc. have crown group definitions
rather than memorize a bunch of fussy, idiosyncratic definitions.

>  Thirdly, we already have a name for the crown-group: Neornithes.  Further, 
> Neornithes has been used for the avian crown-group for a very, very long time.
>  [Gauthier and de Queiroz (2001) propose a whole new definition for 
> Neornithes, and make it *more* inclusive than Aves!]

The definition that they consider (but do not explicitly propose!) is
based on the original usage, which was as an explicit substitute for
_Ornithurae_ that included _Hesperornis_ and _Ichthyornis_ . Its usage
for the crown group is a somewhat recent innovation. (How recent, I'm
not exactly sure, although as late as 1983 Martin included
ichthyornithiformes therein.)

> Yes, that's certainly true.  But by the same token, given that "avian" tends 
> to be used both as (1) an adjective and noun equated with "bird"; and (2) a 
> member of clade "Aves", I think it would be useful if "Aves" includes all 
> those taxa that have traditionally been considered "birds" (avians).  Thus, I 
> think it is preferrable to leave _Archaeopteryx_ in Aves, where it's been 
> ever since its discovery.

Not always -- some researchers have excluded it from _Aves_. And, FWIW
(maybe not much), in popular texts it's often portrayed as something
straddling the line, not clearly belonging to either side.

Personally, I like the idea David Marjanovic proposed, that a clade
resembling the traditional one used in paleontology (which his
definition approximates much better than the node-based definition
does, IMO) could be named "Ornithes" (currently, and somewhat
bizarrely, an unused name). Then there'd be no problem whatsoever
using "bird" to refer to that clade.
-- 
T. Michael Keesey
Director of Technology
Exopolis, Inc.
2894 Rowena Avenue Ste. B
Los Angeles, California 90039
http://exopolis.com/
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