Re: Placement of Segnosauria

["David Marjanovic" <david.marjanovic@gmx.at>]

> Theropods typically have five carpals, with three proximal and two
> distal,

? Are there any theropods with an intermedium? AFAIK, normal is radiale and
ulnare proximally and 1 + 2 and 3 (and 4 basally) distally...

> <...What the description of *Alxasaurus* did in the first place, AFAIK,
> was ["to make clear", I forgot] that *Therizinosaurus* is a segnosaur, not
that either is a
> theropod, and this is what I doubt.>
>
>   How? What is your support for a hypothesis that states that known
> segnosaur material is non-theropodan?
>
> <The illustration in the original paper doesn't convince me. I think
> it's too ambiguous.>
>
>   About what?

About whether mt I contacted the tarsus or not. I'll look at the figure once
more.

> The ascending process is tall with a laterally directed
> flange at least proximally (closer to the hinge of the ankle in this
> case) flush with the lateral margin of the tibia, astragalus comprises
> well over a fifth the tibial length (nearly 25% -- general
> off-the-top-of-my-head estimate, my actual figures are buried
> somewhere), distal end of fibula reduced in diameter distal to the
> anterior fibular flange and is subsequently much less than 1/4 the
> width of the tibia, and greatly reduced in relative diameter, anterior
> iliac blade longer than posterior iliac blade, ventral margin of
> posterior blade curves ventrally in lateral/medial views, lesser
> [=anterior] trochanter flush at the apex with the height of the greater
> trochanter and its form is wing-like, tibia with fibular crest, pubic
> apron relatively shallow [pubis is incomplete distally, but this
> feature is in marked contrast to prosauropods who have very deep aprons
> and shallow pelvic canals.], metatarsal I does not contact distal
> tarsals, medially flattened proximal ends of metatarsals III-IV, manal
> claws very mediolaterally compressed, hinged distal carpal block
> shallowly semi-lunate in extensor/flexor aspects, ventral margin of
> anterior blade of ilium curves ventrally and the blade itself is deeper
> than the posterior blade, even though it is incomplete dorsoventrally
> in both ilia, dorsals and cervicals bear lateral depressions,
> zygapophyses splayed diagonally relative to the horizontal plane of
> each bone, the postzygapophyses expanded distally ... and that's just
> the main block, assuming the posited hypothesis of non-homologous
> blocks. The diagnosis for *Beipiaosaurus* is simple, and the only
> reasonable autapomorphies given (I can find more in text and in
> personal observation) are 1) posterior carinae of dentary teeth
> unserrate with 2) posteriorly convex margins and bulbous bases, 3)
> tooth crowns nearly mesiodistally as long as the crown is high above
> the basal constriction [rephrased from Xu et al., 1999: p. 351
> {fig.2a,b}; _Nature_ 399: 350-354]. So far, these are limited to the
> problematic dnetary, but I doubt prosauropods progressed into the
> Cretaceous either, and therizinosauroid affinities are again stronger
> if you interpret this form as a theropod; prosauropod, and you would
> have extensive postcranial convergences related to carnivory and
> increased cursoriality. I will discuss this form more completely in the
> near future, including my own observations of autapomorpies. Including
> the forlimb material indicates a raptorial form with exceptionally long
> forelimbs, long and slender antebrachium and robuts manus nonetheless
> longer than the antebrachium.

[snip]

OK, OK... I'll read the paper once more and comment later. The ascending
process on the astragalus and the tibia with fibular crest sound quite
convincing, I have to admit.

> <I have looked there, I'm still not convinced.>
>
>   Xu et al., 1999, address the jaw as perhaps too incomplete for
> analysis, but it is not likely to be significant as no clear
> therizinosaur autapomorphies can be distinguished from it, and the
> teeth themselves are more similar to plateosaur teeth anyway and thus
> not useful in consideration of phylogeny.

So I'll wait for more fossils.