Re: oviraptorids-therizinosaurs

["Mickey Mortimer" <Mickey_Mortimer11@msn.com>]

Ken Kinman wrote-

>      I was just rereading the characters which purportedly unite
oviraptors
> and therizinosaurs in a clade, and most are also found in various birds,
> Achillobator, etc.

Let's look in more detail at them then-
- posterior section of premaxilla toothless
This is also found in Compsognathus; coelophysoids and Dilophosaurus to a
small degree, and theropods without premaxillary teeth like Shuvosaurus,
ornithomimids, confuciusornithids, Gobipteryx, Nanantius? valifanovi,
ornithurines and possibly Avimimus.
- promaxillary fenestra absent (reversed in oviraptorids)
This is plesiomorphically found in coelophysoids and more basal dinosaurs,
but developed independently in Torvosaurus and pygostylians.
- nasal subequal in length to frontal
I remeasured nasofrontal ratios for this post and determined they are more
complex than I thought.  Any measurement will involve factors such as the
type of nasofrontal suture, how elongate the subnarial nasal process is,
etc..  Erlikosaurus has a very short nasal, only surpassed by those
theropods with highly transformed snout elements (eg. Irritator,
Confuciusornis, Yanornis).  Oviraptorosaurs' nasals are shorter than most
non-coelurosaurs, tyrannosaurids, Shuvuuia, troodontids, Sinornithosaurus
and Velociraptor, but comparable to Ornitholestes, ornithomimids,
Bambiraptor and avians.  Perhaps apomorphic of segnosaur-oviraptorosaurs,
but perhaps synapomorphic of Ornitholestes+Maniraptoriformes and reversed
later.
- vomers extend posteriorly past maxillae
Only ornithothoracines have this among other theropods.
- ectopterygoid lateral to palatine
Unique to segnosaurs and oviraptorosaurs.
- reduced basipterygoid processes
Ornithothoracines are the only other theropods to have such reduced
basipterygoid processes.
- dentary symphysis decurved
Ornitholestes and some ornithomimids also have this too.
- dentary symphysis deflected medially
This is found in ornithomimosaurs, Avimimus and some troodontids in addition
to the segnosaur-oviraptorosaur clade.
- two pairs of cervical pleurocoels
Basal theropods like coelophysoids, Dilophosaurus and ceratosaurs have this,
as do the deinonychosaurs Achillobator and Variraptor.  Baryonyx exhibits
this only on the third cervical and some cervicals of Avimimus also have two
pairs of pleurocoels.
- ventral sulcus on cervical centra flanked by ventrolaterally directed
ridges
Unique to the segnosaur-oviraptorosaur clade as far as I know.
- cervical prezygopophyses separated by a U-shaped space
Rather hard to define specifically, but the morphology seems unique to the
segnosaur-oviraptorosaur clade.
- caudal vertebrae decrease in length posteriorly
This is also unique to the segnosaur-oviraptorosaur clade, although one
might argue the many vertebrae incorporated into the pygostylian pygostyle
qualify.
?- ulnar facet of humerus expanded, merges with entepicondyle
Still haven't looked at this character closely.
- pubic foot expanded anteriorly
Achillobator has this, as do Sinraptor dongi and Siamotyrannus.  Avimimus is
often shown with it, but the pubis is broken, so this is uncertain.

So you're right, many of the characters supporting a
segnosaur-oviraptorosaur clade are seen in other theropods.  However, such
things are expected, as we are dealing with theropods, some of the most
homoplasious taxa around.  Still, four completely unique synapomorphies is
something for a suprafamilial theropod clade.

>       Don't know where Norell et al. will place therizinosaurs, but I
still
> think they split off before an oviraptorid-caudipterid clade.  And this is
> reinforced by the apparent primitive nature of therizinosaur eggshells
> (dinosaur sphaerulitic).
>        Birds, dromaeosaurs, and oviraptors (and probably caudipterids as
> well) share ornithoid eggshells (and mononykines probably did as well).
> Therizinosaurs apparently did not and therefore I also remain unconvinced
> that they form a clade with oviraptors.

Ah, good.  Using actual character evidence to support your ideas.  However,
your argument is flawed.  The primitive condition for
avetheropods/neotetanurines was prismatoolithid (prismatic), as seen in
allosaurids.  Thus, the presence of dendroolithid (dinosauroid-spherulithic)
eggs in segnosaurs is not the primitive condition.  It could have evolved
from prismatic eggs or ornithuroid eggs.  You don't mention troodontids,
which have prismatoolithid eggs like allosaurids, but are currently placed
in the (Oviraptor + Deinonychus + Aves) clade.  They must have reversed, or
else oviraptorids developed ornithuroid eggs in parallel to eumaniraptorans.
If that can happen, certainly segnosaurs could have changed their eggshell
type too.

>        And the polymorphic nature of alvarezsaurids is again raising the
> possibility in my mind that Alvarezsaurus is not in an exclusive clade
with
> Mononykines.  I think the latter are more closely related to birds than
> Alvarezsaurus is.

Bah!  Did you know Alvarezsaurus has a large flattened first manual ungual
like Patagonykus and Mononykus (Novas, 1996)?  The three are very closely
related based on many vertebral, pelvic and hindlimb characters as well.
They are all separate OTU's in my analysis and always come out as
monophyletic.

Mickey Mortimer