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Re: It's Mei day!!



David Marjanovic (david.marjanovic@gmx.at) wrote:

<There's an SVP meeting abstract on more such troodontids. It tries to
link them to birds...>

  There will be more on this set of fossils as time progresses. Sunny
Hwang, primary author of the abstract in question, is in charge of
describing this new Ukhaa Tolgod troodontid, whose skull is featured on
the http://paleo.amnh.org/ website under the Gobi expeditions header as
"Shuvuuia." It actually has a very nice skeleton, mising mostly whole
sections of vertebrae and the shoulders, but has legs, hands, pelvis, and
two beautiful skulls, that will most certainly aid our understanding of
the form. That form may not see publication until early or mid 2005.
Unlike *Mei,* the Ukhaa troodontid shows NO dorsal expansion of the jugal,
and I think in *Mei* there _was_ a vestigial ramus given the shape of the
expansion ... this is, however, unambiguously absent in the Ukhaa form.
So, there probably is, like in "dromaeosaurs," a basal clade of
troodontids.

  Further info:

  The holotype is IVPP V12733, and derives as noted from Lujiatun, in
Shangyuan Co, near Beipiao City, in Liaoning Province, People's Republic
of China; and comes from the lowermost non-lagerstät-beds of the Yixian
Formation, noted for preserving such 3D specimens as *Liaoceratops,*
*Sinovenator,* *Graciliraptor* [it's all limbs, oy] and *Jeholosaurus.*
*Sinusonasus* derives from these beds, but was preserved as a more classic
"slab" then in tuffaceous rock, as was *Yixiansaurus,* allowing
preservation of integument -- also in *Dilong.* NOTE: the Lujiatun
sediments are VERY much like that of the underlying Tuchengzi Formation,
and this may actually help constrain the age of that latter formation,
given the similarity in preservation style and material quality. The
Lujiatun sediments are dated at 128-139mya, roughly Valanginian to
Barremian, so there is a lot to refine in this datum.

  Measurements:

  Skull (tip to quadrate) -- 53;
  Mandible -- 56;
  Cervical series -- 67;
  Dorsal series -- 92;
  Sacrum -- 30;
  Caudal series -- 257;
  Scapula -- 45;
  Coracoid distal ramus -- 11;
  Furcula one arm -- 18;
  Humerus -- 42;
  Radius -- 39;
  Manus -- 67;
  Femur -- 81;
  Tibiatarsus -- 106;
  Foot -- 105;
  Metatarsal III -- 58.

  Diagnosis of *Mei long*, btw:

  1. "extremely large nares extending posteriorly over onehalf
of the maxillary tooth row;" [This is possibly ontogenetic, as noted by
Tom Holtz.]
  2. "closely packed middle maxillary teeth;"
  3. "maxillary tooth row extending posteriorly to the level of the
preorbital bar;"
  4. "a robust, sub-?U?-shaped furcula;" [Some basal birds like the
*Shenzhouraptor*/*Jixiangornis*/*Jeholornis* complex seem to have this
structure as well, but lack the characteristic S-shaped recurved rami and
the small hypocleidium that *Mei* possesses.]
  5. "presence of a lateral process on distal tarsal IV;" [This is noted
as present in *Microraptor,* a basal dromaeosaur, and apparently the
closest "phyletic" dromaeosaur to *Mei*, so this may actually be a
deinonychosaurian feature lost in all troodontids and dromaeosaurs.]
  6. "the most proximal end of the pubic shaft is significantly compressed
anteroposteriorly, and extends laterally just ventral to the articulation
with the ilium." [it actually is wider than the pubic peduncle, and you
can see this in the fossil illustrations, for an amazing surprise VERY
clear given *Dilong's* non-cranial illustrations.]

  So, 2, 3, 6, and possibly 4 are autapomorphic of *Mei long.*

  Troodontids group together because of:

  1. no basisphenoid recess between basisphenoid and basioccipital (9.2)
[This is also seen in oviraptorosaurs and segnosaurs.];
  2. flat internarial bar (21.1) [This is also present in alvarezsaurids
and ornithomimids, leading Sereno to group them into Ornithomimoidea, and
therefore could also be used to support a Bullatosauria.];
  3. descending process of squamosal does not contact ascending process of
quadratojugal (49.1);
  4. dentary triangular in lateral view (71.0) [This is also seen in basal
dromaeosaurs (= microraptorians) and is a feature noted by Senter et
al..];
  5. nutrient foramina on external surface of dentary lie within a deep
groove (72.1) [More or less ambiguous in *Sinusonasus*.];
  6. moderate number of dentary teeth (25-30) (85.1);
  7. anterior dentary teeth smaller than posterior dentary teeth, more
numerous, and more closely appressed than those in middle of tooth row
(89.1) [I would split this character three ways, given it's a relationship
of anterior to posterior dental separation, and relative size of crowns --
it is, however, also present in *Microraptor* and "Dave," and is more of a
deinonychosaurian apomorphy.];
  8. transverse processes of anterior dorsals short, wide, and slightly
inclined (107.1);
  9. foot asymmetrical with a slender mtII and robust mtIV (205.1);
  10. depression on the ventral surface of the postorbital process of the
laterosphenoid (221.1) [coded as present in "*Ingenia,*" *Caudipteryx,*
*Stenonychosaurus* (aka, *Troodon*), *Saurornithoides junior,* and
*Sinovenator,* so it shows up in non oviraptorids coded and several of the
preserved relevant areas for troodontids known ... it is listed as unknown
for *Mei,* and given the figures and preparation, it would be premature to
code it otherwise.];
  11. basal tubera small, directly below condyle and foramen magnum, and
separated by a narrow notch (222.1).

  The authors also note a peculiar feature of *Mei* in that both pedal
phalanges pdII-1 and pdII-2 have a caudoventral heel underlying the
previous element's distal articular surface. This is present in *Mei,* but
is also present in GIN 100/44 (EK troodontid in Xu and Norell's analysis),
*Borogovia gracilicrus,* some specimens of *Deinonychus antirrhopus* and
*Stenonychosaurus inequalis,* *Adasaurus mongoliensis,* *Velociraptor
mongoliensis,* and *Saurornitholestes langstoni;* dorsal inclination of
the proximal articular surface of pdII-1, thus giving pdII-1 a "heel"-like
structure without a developed process, occurs in other troodontids
(*Saurornithoides mongoliensis,* some specimens of *Stenonychosaurus
inequalis,* and some specimens of *Deinonychus antirrhopus*) but is
otherwise apparently unrelated. Such heels on pdII-1 are typically absent
in terrestrial theropods (pers. obs.) with the exception of small forms
that bear a dorsal inclination of the proximal articular surface, so I
would primarily consider this unrelated to the presence of absence of a
"heel," whereas such a "heel" on pdII-1 itself may be phylogenetically
informative. The authors did not include any pedal phalangeal characters,
so other troodontid apomorphies (pdII-2 less than 80% the length of
pdII-1, for example) were not included.

  P.S., May Day is another name for Beltane, a thouroughly NON-Christian
holiday (following in the tradition of the Saturnalia and Samhain in
"cleansing" Pagan harvest holidays) celebrating fertility by rite of women
and men playing around a phallic symbol now known as a "maypole." There
are TOO many jokes to be made at the expense of this little dinosaur, but
as I said in my first post, finally, a break from the tradition of Sin-
and -saurus :).

  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)


                
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