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Thoughts on Tanycolagreus



Thanks to Ken Carpenter for making his paper on *Tanycolagreus topwilsoni*
available. This allowed me to make general observations. Rather than an in
depth analysis, I will list my initial observations and some comparisons.

  TPII 2000-09-29 is represented by a partial skeleton including all portions,
and in reasonable completeness to infer some proportional data. Unfortunately,
included teeth are so poorly preserved as to offer very little positive
information.

  Carpenter et al. describe the premaxilla as short and deep, and comparing
well enough with a premaxilla referred to *Stokesosaurus clevelandi* that they
referred the bone as a paratype of *T. topwilsoni* (UUVP 7821), leaving *S.
clevelandi* represented by ilia, an inschium, caudal vertebrae, and a partial
braincase. Numerous features of the suggest that Carpenter et al.'s inclusion
of *T. topwilsoni* into the Coeluridae may not be correct. These include the
short and deep premaxilla, a lachrymal with a long ventral orbital flange that
would extend along the ventral margin of the orbit above the jugal, a
postorbital with an anterior process projecting into the orbit. These features
are variously, and almost consistently, found in few theropod groups, including
Abelisauria and Tyrannosauroidea. The quadratojugal is very similar to
*Ornitholestes hermanni*, and the nasal lacks an ornamentation, but is simple,
unlike *Dilong paradoxus*. A large dorsal process of the articular buttresses
the posterior margin of the articular fossa for the quadrate, and is the
deepest portion of the articular.

  The scapulocoracoid bears the distinct large acromion with the vertical
height typical of tyrannosauroids, though the distal end is not as expanded as
tyrannosauroids are. The humerus is very straight with a mildly inflected
distal end and strongly inflected proximal end; the distal end is roughly
quadrangular, and the epicondylar crests are weakly developed; the distal
condyles are strongly inflected cranially and subspherical, and very close
together, otherwise reminding me of therizinosauroids. The manus is virtually
identical in *T. topwilsoni* and *D. paradoxus* and I am hard pressed to find a
comparable manus except in *Nqwebasaurus thwazi,* which is suprising enough,
though in *D. paradoxus* as in *T. topwilsoni* the third metacarpal is
extremely gracile (as mentioned previously by Mickey Mortimer,
http://dinosaurmailinglist.cmnh.org/2004Oct/msg00094.html) and the first
metacarpal is only slightly shorter than half the second metacarpal's length;
third and first metacarpals are nearly identical in length. The manual unguals
remind me of nothing less than therizinosauroids, except they lack the dorsal
lip of the articular surface, and the first ungual is largest and least
strongly curved.

  The pubes of *D. paradoxus*, *Coelurus fragilis*, and *T. topwilsoni* are all
extremely comparable and similar, with a large posterior boot and virtually no
anterior boot, though *T. topwilsoni* has the largest anterior projection of
the three and this region is curved dorsally and forms a rim similar to the
"boat-shaped" pubes in tyrannosaurids, and reminds me very closely of
*Shanshanosaurus houyanshanensis*. The femoral head is raised and
subrectangular in aspect with a deep ventral emargination and flange extending
ventrally, and there is no constriction between the caput and trochanters,
forming a "cervix"; a primitive lowe anterior trochanter forming a wing-shape
anterior to the femoral shaft and well-divided from the caput is a primitive
feature not found in tyrannosaurids, whereas the absence of a femoral cervix is
typical of tyrannosauroids. A very proximal and weak fourth trochanter is a
coelurosaurian feature and the femoral caput shape is characteristic of
tyrannosauroids, also shared with a femur of *C. fragilis*. The tibial cnemial
crest projects dorsally and above the femoral articular surface; the astragalar
ascending process is also very tall and triangular in shape, rather than
quadratic as in *O. hermannii* or *C. fragilis,* as shared with tyrannosauroids
and maniraptoriforms. As in *D. paradoxus*, a slight consistriction of
metatarsal III between II and IV is present, though in *T. topwilsoni* this
constriction appears to be more pronounced; unlike *O. hermannii*, the
metatarsals are much broader compared to anteroposterior depth, and are not as
extremely elongated as in *C. fragilis*.

  Limb proportions between *D. paradoxus* and *T. topwilsoni* appear to deviate
by only 0.025 average.

  Several analyses including Sereno's and Holtz' has found that "coelurids"
have variously been placed as basal Maniraptora, outside Maniraptoriformes, or
just outside Tyrannoraptora and as basal Coelurosauria. Nonetheless, as with
Tyrannosauroidea, they tend to shift position a bit. Plasticity of character
features may account for this, as well as conservativism of non-maniraptoriform
coelurosaur anatomy. I imply here that non-compsognathid non-maniraptoriforms
may actually form a close-knit radiation that can be variously interpreted as a
clade uniting tyrannosauroids and coelurids, or with various tyrannosauroids,
coelurids, and miscellaneous taxa including *Proceratosaurus bradleyi* that
form successive outgroups to Maniraptoriformes. Nonetheless, the similarities
between *T. topwilsoni* and *D. paradoxus* are unmistakable and provide the
following hypothesis:

  *Tanycolagreus topwilsoni* is the most basal member of Tyrannosauroidea, and
provides the most complete skeletal evidence for Tyrannosauroidea in the Upper
Jurassic, affirming *Aviatyrannis jurassica* and *S. clevelandi* as
tyrannosauroids.

  Further data would arrive in the form of a more indepth analysis and
inclusion of *T. topwilsoni* into a cladistic analysis, such as Holtz' latest
monster, and the presence of two tyrannosauroids in the Morrison Formation may
argue that *S. clevelandi* and *T. topwilsoni* are synonyms, yet the only
comparable material so far are caudal vertebrae.

  Food for thought? This is, of course, all superficial.

  Cheers,

Jaime A. Headden

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

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