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

Re: Segnosaurs again (was Re: Dinosaur Web Pages' Re-Opening)



In a message dated 97-09-05 23:02:32 EDT, znc14@ttacs1.ttu.edu (Jonathan R.
Wagner) writes:

<< At 08:10 PM 9/4/97 -0400, Dinogeorge wrote:
 >I know of >no< cladistic analysis of segnosaurs in which the group is
 >considered to lie outside Theropoda. All the analyses _a priori_ assume
 >they're theropods and then try to figure out where they go. It is
appalling,
 >given how many characters segnosaurs share with prosauropods and
 >sauropodomorphs, that nobody has done this.
         And that's what really burns your theory, isn't it? Russell and Dong
 found _Alxasaurus_ to be so clearly theropodian that they didn't think it
 was worth the effort to do such an analysis. You cannot blame the demon
 cladistics for this one, George, because these folks figured it out YOUR
way.>>

Sorry, but you're quite wrong here. Russell and Dong figured _Plateosaurus_
into their analysis. And get this: _Plateosaurus_ was found to be primitive
in all characters but three in their matrix: #3, medial alae from premaxillae
meet in front of vomers; #20, denticles on teeth small, teeth with
constricted roots [two characters here, actually]; and #36, ulnar facet [f]or
humerus expanded and merges with entepicondyle. All three derived characters
are scored >the same way< for _Alxasaurus_; no reversals. In other words,
according to their analysis, one can go from _Plateosaurus_ (well,
prosauropods, since _Plateosaurus_ is a pretty derived prosauropod) to
_Alxasaurus_ >without reversing a single derived character back to its
primitive state.< (According to my analysis, these three or four characters
are in fact among the shared derived characters uniting prosauropods and
segnosaurs.)

Russell and Dong's character matrix for therizinosauroids >doesn't come
close< to matching any of the analyzed theropod groups in its suite of
derived states. Go back to the paper and examine the character matrix
closely. Compare it with the other theropod groups. If therizinosauroids are
theropods, try to figure out which derived characters the common ancestor of
therizinosauroids and any other of the theropod groups must have had. Add up
the reversals of some of those derived characters that must then be undergone
by this hypothetical common ancestor's descendants in order evolve into those
other theropod groups. It becomes quite ridiculous.

<<         As far as I know, everyone who has seen the specimens, looked over
 the material, and heard the arguments, cladist or not, agrees that
 therizinosaurs are theropods, other than you and Tracy Ford (hi Tracy!). So
 now, since the methods you espouse have failed to convince everyone else,
 you call for a cladistic test? Yet you have already said you won't believe
 one... >>

I don't care how many people believe that segnosaurs are theropods; five
billion people can all be wrong. They've failed to mount a case that
convinces >me<. And I'm a pretty reasonable person; I'll listen to anyone and
read all the relevant literature.