Re: Dinofest Report #2 (and final)

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

At 08:17 PM 4/24/98 -0400, Johnathon Woolf wrote:
>> >In his Saturday talk on North American oviraptorosaurs, Hans-Dieter Sues
said
>> >his research implied that arctometatarsaly arose multiple times,
>> >and that Arctometatarsalia is not a valid taxon.
>>         Note that I assume here that the comments quoted above are an
>> accurate reflection of Dr. Suess' talk.
>
>His heavy accent makes it a bit difficult,

I've never really thought of Sues as having a heavy accent.  Oh, well...

>and I've paraphrased some things, but
>that is what I understood him to be saying.

What he was saying is that some of the original component taxa of
Arctometatarsalia, minimally, are no longer included in it.  So what?
Removing the pelycosaurs from Archosauria doesn't invalidate Archosauria.

>> Arctometarsalia remains "valid" although the concept of all taxa possessing
>> an arctometarsus forming a monophyletic group exclusive of all other taxa
>> may not.
>
>Let me see if I understand this correctly:
>
>1. Arctometatarsalia was named after,

Yes.

>and defined based primarily on,

Actually, the diagnosis is NOT primarily based on the foot.  Geez, you'd
think people might read a paper once in awhile...  There are other,
non-hindlimb characters which unite at least the tyrannosaur-bullatosaur group.

>a specific
>synapomorphy, the pinched 3rd metatarsal. This feature was thought to
indicate a
>close evolutionary relationship among these taxa.  The name was therefore
chosen
>to reflect this relationship.

And because I didn't want to add another name tied into the name of a
preexisting genus.

(And, for the record, the clade name and the synapomorphy name originated on
the same day).

>2. This feature is apparently not synapomorphic among the taxa included in
>Arctometatarsalia.

No, it IS synapomorphic for the Arctometatarsalia.  However, it is not
UNIQUELY synapomorphic for Arctometatarsalia.  However, just because the
derived state "leglessness" occurs independantly in other squamates doesn't
mean it isn't a synapomorphy of snakes.

>Therefore, these taxa are not more closely related to each
>other than any of them is to other theropods.

No.  There are still some forms possessing the derived condition which are
more closely related to each other than to other theropods.  The "new"
cladogram Sues showed reflected that, with a
tyrannosaur-troodont-ornithomimosaur group (1 appearance of the character)
and a caenagnathid-oviraptorid-therizinosauroid group (a second appearance,
in caenagnathids).

Indeed, the main reason Sues brought up the point was to show that the
condition appeared independantly in caenagnathids than in other forms,
regardless of the number of times the other forms evolved it.

>3. Even though the relationship after which the clade was named does not exist,
>the clade is still valid.

?  Where are you getting this?

>That makes absolutely no sense to me.

That's because you're not paying attention...

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661