Re: Questions

["Jaime Headden" <ja_headden@qilong.8m.com>]

Steve Mahon () wrote:

<1.secondary palate formed from premaxilla & maxilla.Is that Ornithomimosaurian
or Ornithimimid?>

  This exists in various taxa, including Ornithomimosauria (present in
*Pelecanimimus,* *Garudimimus,* and *Harpymimus* as well as ornithomimids), in
*Shuvuuia*, and in oviraptorids, but not in *Caudipteryx* apparently, is unknown
in caenagnathids (as yet). More likely, this character should be: "maxillae join
above or in front of the vomer, forming with the vomers and medially conjoin
premaxilla a secondary palate" . In this case, this feature is present in
spinosaurids, definately known in *Baryonyx* and *Suchomimus*, the possibly
synonymous *Cristatusaurus*, and a spinosaurine snout referred to *Spinosaurus
maroccanus.*

<2.ulna bowed posteriorly. Maniraptoran or Maniraptoriformes?>

  This occurs in possible non-maniraptoriforms like *Ornitholestes* and
*Coelurus,* so it is likely this is not a "maniraptoriform" or more-inclusive
character unless the taxa above are also maniraptoriform. *Sinosauropteryx* also
appears to have a minute version of this, but *Compsognathus* would seem to not
hav it.

<3.does Troodontidae have the Eumaniraptoran characters from my previous
thread?>

  Troodontids are technically eumaniraptorans because they tend to be the sister
group to dromaeosaurids; dromaeosaurids + birds = Eumaniraptora, in a broad
sense. Some of the answers you seek are in various papers in Nature, and from
authors such as Tom Holtz and Paul Sereno, and if you ask very nicely, I am sure
they'd be willing to help ya out :) . Copies of pdfs of the Nature papers are
floating around the net somewhere, so certainly these can be found fairly
easily.

<4.are the Alvarezsaurid-Archaeopteryx characters (from the previous thread)
found in any of the forms above?>

  Various of them. The base of Maniraptora to the base of Avialae are rife with
convergent characters, which have led to alvarezsaurs inside Aves, just outside
of it as avialaeans, and atthe base of Maniraptora itself, as well as outside
it. *Archaeopteryx* never changes position, relative to other early birds,
near-birds.

<5.Does Sinornithosaurus have the Dromaeosaurid characters?>

  These would be the shape of the squamosal, having a forward-set and inclined
quadratojugal process with lateral ridge from the postorbital to the
paroccipital process; a complex of a metatarsal II about as long as the mtIV,
with a large sickle claw and hyperextensible digit having a second phalanx over
75% the length of the first phalanx, and the claw being over twice the length of
the first phalanx (the reverse of many of these features are found in
troodontids, which have short and thin second metatarsals, a short second
phalanx, and smaller claw -- *Sinovenator* also lacks some "troodontid"
characters, as befits being basal, but even *Microraptor* has dromaeosaurid
characters); and most notably, the presence of elongated prezygapophyses on the
caudals posterior to the 10th which overlap more than one preceeding caudal, and
chevrons that do the same.

<6.nasal anteroventral process absent in Troodontids & any of the birds listed
above?>

  Among the taxa listed, only some troodontids seem to lack the process; for
instance, *Byronosaurus* has it, it just doesn't touch the premaxilla underneath
the external naris. *Confuciusornis* has the process, and you can't tell in
*Passer* because the whole region is fused.

<7.Ornitholestes has cervical epipophyses not overhanging the postzygapophyses &
posterior dorsal neural spines lower than long?>

  The description of *Ornitholestes* is being worked on by some notables at the
AMNH, so we are waiting the answer to this. However, as from the original
description and personal observation of the mount, posterior dorsal neural
spines are higher than craniocaudally long, and the epipophyses are not
elongated at all, as seems to be noted in all small theropods

<.quadrate slopes anteroventrally, lower jaw is offset antreriorly & articulates
below the orbit in what Ornithomimosaurians?>

  In *Ornithomimus,* *Struthiomimus,* *Dromeciomiomus,* and *Gallimimus,* yes --
and also in *Pelecanimimus.* In *Garudimimus* and *Sinornithomimus,* almost but
not quite, as this region is a lot more vertical, and in *Harpymimus* you can't
tell without a quadrate (missing). It would seem to be a two or three step
acquisition either way ya look at it: 1) it is acquired in basal
ornithomimosaurs, lost immediately after *Pelecanimimus*, and reacquired in
ornithomimids (three steps); or 2) is it acquired in ornithomimids and
*Pelecanimimus* convergently (two steps). Most likely the machine will find the
latter the more parsimonious situation if the other characters are congruent. So
far, no topology has failed to place *Pelecanimimus* at the base of
Ornithomimosauria, so we shall see.

<9.All taxa (minus Allo.) have the following: *expanded circular orbit*ischium
short, 2/3 or less length of pubis*loss of ischial foot*triangular obturator
process on ischium*ascending process of astragulus greater than 1/4 length of
tibia-astragulus*15 or less caudals w/ transverse processes*6 sacral
vertebrae*extensive stiffening of tail*reduced femoral 4th trochanter*, or if
unknown in any taxa above.>

  Well, this is a serious complex that is no longer apparently true; though
studies show that the bigger skull you have, the less circular your orbit is
going to be (Henderson, 2003), you will get large tyrannosaurids with vertically
oval orbits, but also dromaeosaurids with horizontally oval orbits, not
circular, as occurs in basal oviraptorids and in *Shuvuuia* and *Archaeopteryx.*
*Sinosauropteryx* and *Compsognathus*, as well as compsognathids from Brazil,
have trapezoidal obturator processes, as in *Allosaurus* (even basal allosaurids
have the closed obturator, so this is convergent). Tyrannosaurids and nearly all
ornithomimids have an ischial foot. Ornithomimosaurs also have a long ischium.
Some coelurosaurs have short ascending processes of the astragalus, from less
than 1/5 in *Beipiaosaurus* and therizinosauroids. Oviraptorosaurs and
therizinosauroids have most caudals with transverse processes, and *Shuvuuia*
has many more caudals than 15 with processes. 6 sacrals (or more) are only found
in ornithomimids like *Gallimimus,* oviraptorids where known, troodontids,
*Ornithodesmus,* *Confuciusornis* and higher birds, and tyrannosaurids.

  Stiffening of the tail is a tricky issue, because it appears to occur
throughout Theropoda, and is not limited to the Coelurosauria or to Tetanurae
(the latter was named for this feature: tetano- (stiff) + oura (tail) ); it is
present in *Coelophysis* (Gay, 2001), *Herrerasaurus* (pers. obs.),
*Allosaurus,* and coelurosaurs in general. Some coelurosaurs lack the condition
or extensively overlapping caudal prezygapophyses, including the oviraptorosaur
+ therizinosauroid clade, birds including *Archaeopteryx,*

<10.any basal taxa above (Tyrannosaurs, Coelurus, Ornitholestes, Compsognathids)
that have the following:*seperate exit for the cranial nerve V*articulars &
quadrates pneumatized*3rd antorbital fenestra*elongated anterior cervical
zygapophyses*obturator process on ischium is distal*ischium ends in point*length
of forelimb 75% of presacral spine*ulna bowed posteriorly*semilunate carpal,
which permits the hand to flex both laterally & dorsoventrally*thin, bowed
metacarpal III*, or if unknown in any above taxa.>

  A semilunate carpal is known for *Allosaurus* (Chure, 2000) and in
*Acrocanthosaurus* (Carpenter and Currie, 2000). The distal obturator process
should be a component percentage of the position from one end versus the total
length of the ischium; in some coelurosaurs, it is in the proximal 30% of the
ischium, as in most non-maniraptoran forms, while in ornithomimosaurs, it is in
the proximal 20%; in maniraptorans, it is either at 40% or more distal, but in
birds becomes much more proximal or is lost (or becomes more distal, as in
*Archaeopteryx*). The ophtalmic branch of the trigeminal nerve (V-1) branches
off only in coelurosaurs; so far, no non-coelurosaur has this condition, and it
seems to occur randomly in some coelurosaurs, as well (*Sinraptor* has it, too,
but *Allosaurus* does not; it's in dromaeosaurids, oviraptorids, *Erlikosaurus,*
tyrannosaurs, troodontids (which in Judithian braincases also have a separate
exit for all three branches of cv-V), as well as in birds, but there's only one
foramen in ornithomimosaurs; in tyrannosaurids and troodontids, the tract for
the ophthalmic branch is entirely in the laterosphenoid, forming a distinct
canal, and this is absent in other taxa save oviraptorids where the suture
between laterosphenoid and prootic are visible [pers. obs.]). I already
commented on the ulna. The metacarpal III being thin and bowed only occurs in
maniraptorans, as even the "coelurid" *Nqwebasaurus* lacks it, as does
*Sinosauropteryx* and all taxa above Maniraptora itself; one could argue that
tyrannosaurids where present have a thin mcIII, as would alvarezsaurids and
*Compsognathus,* but the bowing is not observed in these taxa. The arm increases
to 75%+ the presacral column in few animals, including Eumaniraptora;
oviraptorids, for having such short arms and long necks, do not apparently have
this, and in some therizinosaurids, the arm is extremely (and convergently)
elongated. Pneumatization of cranial elements is tricky and not all that
conclusive among theropods except those few coelurosaurs tested; *Allosaurus*
lacks these pneumatic bones, but has a pneumatic braincase, unlike other
non-coelurosaurs.

  Hope this helps and cheers,

  Jaime A. Headden

  Little steps are often the hardest to take. We are too used to making leaps in
the face of adversity, that a simple skip is so hard to do.  We should all learn
to walk soft, walk small, see the world around us rather than zoom by it.

  "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)