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Re: Dinosaur Web Pages' Re-Opening
>Your web site is beautifully done and lots of fun to mess around in. The dino
I wholeheartedly aggree!
>(1) Saurischia doesn't exist, or if it does, it is congruent to Dinosauria
Under the terms of phylogenetic taxonomy, by your phylogeny, the two
would be not be synonymous. Dinosauria is the stem based clade of the common
ancestor of _Triceratops_ and Neornithes AAOID, Saurischia would be
synonymous with Theropoda (all dinosaurs more closely related to Neornithes
than to _Triceratops_(?), or Sauropodomorpha).
>All the characters that are listed by, say, Benton in _The
>Dinosauria_ that supposedly unite Theropoda and Sauropodomorpha into a clade
>Saurischia are either plesiomorphies, homoplasies, or doubtful.
See Gauthier 1986
To paraphrase nearly every current systematicist, the only way one
can determine that a character state is plesiomorphic or homoplastic is by
phylogenetic analysis. Very few scientists will be interested in the a
priori assumption of homoplaisy.
Incorporated here as a basis for the following are Gauthier 1986,
numerous Benton and Sereno articles, Novas 1997, Holtz 1994 and 1996, ad
>[...] important characters uniting the two groups into the clade
>Phytodinosauria [i]nclude twin sternal plates,
This is likely to be plesiomorphic.
Plesiomorphic for dinosauria? I do not recall evidence for off-axial
dermal armor in any primitive dinosaur (and there is evidence for axial
dermal armor in all three groups). I believe "_Lagosuchus_" has scutes. Is
there any evidence tat early "phyotdinosaurs" had a greater degree of dermal
>a functional fifth pedal digit
Plesiomorphic for Ornithosuchia, and possibly more inclusive clades.
I realize you (George) cannot accept reversals in the locomotor apparatus,
but such an objection cannot be supported in the presence of clear
phylogenetic analyses to the contrary. I do not recall there being any basal
Ornithiscian with a functional fifth digit...
>leaf-shaped herbivorous dentition.
As noted by Gauthier (1986), this morphology is a common adaption of
reptilian tooth pattern, as it occurs in lacertillians as well as several
archosaur groups. While it is a potential synapomorphy, the diagnostic
utility of this feature is doubtful.
>(3) Heterodontosaurids are not ornithopods [...]
>and there is [not] an obturator process on the ischium.
It is possible that many of common conceptions concerning the
diagnostic utility of this element are in error. I would argue that the
*absence* of the obturator process is by no means significant, excep tint he
context of one being present ancestrally, as it appears to have dissappeared
several times over dinosaurian history, and may have even been redeveloped
in some lineages.
See Britt 1992 and Novas 1997.
>(4) Segnosaurs (= therizinosaurs) are not theropods.
Therizinosaurs (= segnosaurs).
>theropods, the semilunate carpal evidently formed by fusion of the proximal
>carpals (radiale and intermedium), whereas in segnosaurs it formed by the
Hasn't this particular homology been questioned? I believe that
Hinchcliffe's (?) work on avian ontogeny has some things to say about this.
>carpal structure differs greatly from that of theropods and cannot be derived
"Always with you what cannot be done..."
>from theirs. The forelimb and manus of segnosaurs are highly specialized, so
>the fact that it the manus is tridactyl should not be used as a character
>uniting segnosaurs with theropods.
This is patently ludicrous! Ornithomimids has a far more specialized
manus, and no one argue the homology of their manus! Again you eliminate
homology a priori of a phylogenetic analyses.
>The ascending process on the astragalus differs in detail from that found
in >theropods and probably developed independently.
So your argument then becomes "any feature which is significantly
derived from the ancestral condition may no longer be considered
homologous"? Let's let the data speak for themselves: therizinosaurs and
other theropods have large astragalar as.p.s.
The feet show clear signs of being secondarily quadradactyl (Russell
and Dong 1993).
The lower jaw of _Erlicosaurus_ is similar to that of _Harpymimus_,
as P. Buckholz [sic? sorry Pete] has pointed out.
These teeth are possibly just as similar to those of _Mononykus_ and
_Pelecanomimus_ as they are to your "phytodinosauria".
Retroverted pubes are present in some maniraptors, and anyway are,
in this case, possibly related to herbivorous habits and are thus not to be
excluded from the possibility of convergence.
CHARACTERS WHICH INDICATE THAT THERIZINOSAURS ARE CEOLUROSAURS:
1. Manus tridactyl
2. Manual proportions similar to other ceolurosaurian groups
3. Lip on manual ungual II (Archaey, Oviraptorsauria)
4. Enlarged preacetabular portion of Ilium (Neotheropoda)
5. Elongate ascending process of astragalus
6. Leaf-shaped teeth (Ornithomimidae, Mononykus)
7. Preacetabular blade of ilium dorsovetrally elongate (ovir, microv)
8. " " " with hooked anterior margin (ornith, ov)
9. Antero-dorsal expansion of lip of acetabulum (ov, microv)
10. Obturator process triangular (ceolurosauria)
11. Pubic boot enlarged.
12. ?Ventral migration of obturator process (questionable)
13. Strap-shaped scapula (Theropoda)
14. Tridactyl pes (reversed in Therizinosauroidea)
15. Semilunate carpal with transverse trochlea backs dig I and II
etc etc etc...
>and limbs of segnosaurs all derive much more readily from prosauropod-like
>sauropodomorphs than from theropods
And snakes derive more readily from eels, but that doesn't make it
>(5) _Mononykus_ is not a bird, nor is it an alvarezsaurid. It's a perfectly
In the absence of a phylogenetic hypothesis to the contrary, we are
left with this conclusion. Care to clade a better one?
>good arctometatarsalian or avimimiform theropod with a highly derived,
Avimimiform? Do you have access to material on this taxon that the
rest of us do not? I am interested to know what autopomorphies _Avimimus_
and _Mononykus_ might share, which the latter taxon does not share with
birds or arctomets.
| Jonathan R. Wagner "You can clade if you want to, |
| Department of Geosciences You can leave your friends behind |
| Texas Tech University Because your friends don't clade |
| Lubbock, TX 79409 and if they don't clade, |
| *** email@example.com *** Then they're no friends of mine." |
| Web Page: http://faraday.clas.virginia.edu/~jrw6f |