Re: Haha, more questions

["Mickey Mortimer" <Mickey_Mortimer111@msn.com>]

Dino Rampage wrote-

> Many, many thanks to those kind souls who have offered me much help on the
> evolutionary relationships * ecological niches on Mesozoic mammals. I
still
> have even more questions... you know, I never seem to run out of questions

Nick gave some good answers, here's what I have to add-

> 1) What is Dryptosaurus' relationship to other theropods? All seem to
agree
> that it is a non- maniraptoran coelurosaur, but is it close to the base of
> Coelurosauria, or more closely related to the Tyrannosaurs? I've seen it
> mentioned somewhere on the list that Dryptosaurus was a basal
Tyrannosauroid
> (note the word "TyrannosaurOid")

Holtz (2001) found it to be a basal tyrannosauroid, in a polytomy with
Stokesosaurus and Eotyrannus + Tyrannosauridae.  Similarily, Williamson and
Carr (2001) found it to be a tyrannosauroid more basal than the Gorgosaurus
+ Albertosaurus + Daspeltosaurus + Tyrannosaurus clade, as well as a couple
undescribed American tyrannosauroids.  Also, my old studies usually placed
it as a tyrannosauroid.  Coelurosaurian characters include the tall
astragalar ascending process, deeply concave anterior astragalar surface (in
ventral view) and lack of a transverse groove across the astragalus.  It
seems to be basally positioned in the clade due to its proximolateral
ischial scar, elevated femoral head and aliform lesser trochantor.
Similarities to tyrannosauroids include an enlarged surangular foramen(?),
anteriorly concave pubic shaft and unique proximal metatarsal IV morphology.
It's important to note that there are no described synapomorphies
specifically shared with Deltadromeus, to which is is often compared (both
are large and start with D I suppose....).  Indeed, the ascending process'
height suggests it is more derived.

> 2) How is Troodon related to the other coelurosaurs? They used to be
called
> Arctometatarsalia, then Bullatosaurs, and now their placement is somewhat
> uncertain. Do they occupy a place within the maniraptoriforms, like the
> tyrannosaurs & ornithomimids, or within the maniraptors, or as Oyvind M
> Padron's cladogram states, within the Deionychosauria itself??

The most popular answer now is that troodontids are deinonychosaurs (Sereno,
2000; Longrich, 2001; Xu et al., 2002), or at least paravians (Holtz, 2001;
my old studies).  Norell et al.'s (2001) hypothesis making them the
enigmosaurian sister group isn't valid, because the inclusion of Sinovenator
(in Xu et al., 2002) didn't support it.  The Bullatosauria idea is pretty
obsolete, being found in Holtz's earlier analyses (1994), Perez-Moreno et
al.'s (1994) analysis which included no potential paravian synapomorphies,
and Makovicky's (1995) analysis based solely on vertebral characters.
Sinovenator makes Bullatosauria even less probable, given it's
eumaniraptoran characters and lack of a parashenoid bulla.  These birdlike
characters may be numerous enough to move troodontids from the basal
paravian position they were in in my old analysis, to the Deinonychosauria
as in Xu et al. (2002).  Then again, these deinonychosaurian characters may
end up being more widespread within Paraves, as Sinornithosaurus,
Microraptor, Rahonavis etc. have many of them and could be avialans.
Indeed, I feel there is the possibility troodontids are basal avialans
(which occurred in a few of my old analyses).

> 3) Alvarezsaurs. Weird avialans, weird troodont relatives, or weird
> ornithomimid relatives?

Non-avian maniraptorans.  Sereno's (2001) arctometatarsalian hypothesis is
flawed due to his character selecting methodologies.  Longrich (2001) and Xu
et al. (2002) have both found trees where alvarezsaurids are basal
maniraptorans.  Holtz (2001) and my old analyses support them as
non-eumaniraptoran paravians.  This latter arrangement could lead to a
troodontid sister relationship, though I've never seen such appear in a
cladogram.  A more plausible relative is Avimimus (which was very common in
my analyses), though the current consensus is that it's an oviraptorosaur.
Chiappe (2001) still finds them to be derived avialans, sister to Aves.
Though less common than the basal paravian result in my old analyses, this
did occur from time to time.

> 4) Is Megaraptor believed to be an aberrant giant Gondwanan dromaeosaur?

It would seem to be a paravian of some sort, possibly eumaniraptoran.  See
http://www.cmnh.org/dinoarch/2001Feb/msg00415.html for my opinions.
Basically, the ulna, manual phalange and metatarsal have coelurosaurian and
maniraptoran characters, and the metatarsal and pedal ungual resemble
troodontids, deinonychosaurs and basal avialans.

Mickey Mortimer