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This is one of the new genera in the Silk Road
volume.
Hudiesaurus Dong 1997
H. sinojapanorum Dong 1997
Etymology- " butterfly lizard found by the Chinese
and Japanese", from hudie, Chinese pinyin for butterfly and honoring the members
of both China and Japan for participating in the expedition.
Late Jurassic
Kalazha Formation, Xinjiang, China
Holotype- (IVPP V 11120) (30-34 m) first
dorsal vertebra (550 mm)
Referred- (IVPP V 11121-1) (23 m) humerus (1.21 m),
radius (790 mm), ulna (740 mm), carpal, metacarpal I (150 mm), phalanx I-1 (70
mm), pedal ungual I (210 mm), metacarpal II (310 mm), phalanx II-1 (60 mm),
metacarpal III (330 mm), phalanx II-1 (65 mm), phalanx III-2 (45 mm), metacarpal
IV (310 mm), phalanx IV-1 (85 mm), phalanx IV-2 (20 mm), metacarpal V (250 mm),
phalanx V-1 (74 mm)
(IVPP V 11121-2) four teeth
Diagnosis- "prepophysis" present (see description);
prespinal lamina (also in titanosauroids and diplodocoids); extremely robust
humerus (width of distal end 40% of length).
Description-
The holotype specimen was adult, based on the fused
neurocentral suture, and measured approximately 30-34 meters. The larger
estimate is based on comparison between anterior dorsal vertebrae of the
holotype of Mamenchisaurus hochuanensis, which is 22 meters long. Note
that if Nurosaurus or Abrosaurus are used as comparison, the length is decreased
because these genera have five less cervical vertebrae. Perhaps 30 meters
would be more accurate in this case. The specimen the forelimb belonged to
is estimated to have measured 23 meters, based on the tibiohumeral ratio in
Mamenchisaurus? youngi and scaling to M. hochuanensis.
The teeth were found in the same beds as the
referred forelimb. They are spatulate and serrated anteriorly and
posteriorly. The photo would seem to indicate that two premaxillary teeth
were found in a fragment of the premaxilla, although it could simply be
sediment. The other two teeth are maxillary teeth.
The holotype dorsal vertebra is the first based on
the positions of the parapophyses and diapophyses. It is strongly
opisthocoelous (length 390 mm without anterior ball), with large
pleurocoels. The neural spine is transversely broad and slightly
bifurcated. There is a small median dorsal process between the fork.
An autapomorphic 84 mm process projects anteriorly from the neural
spine and is termed the prepophysis by Dong. He hypothesizes this process
may have been an insertion point for muscles or articulated with the
hyposphene. The hyposphene and hypantrum are present. The laminae of
the neural arch and spine are said to be very similar to Mamenchisaurus.
Differences listed include a V-shaped posterolaterally projecting lamina on the
lateral mergin of the neural spine and a well-developed median lamina on
the anterior neural spine. The parapophysis lies beneath the pleurocoel
and the diapophysis is directed ventrolaterally. The transverse processes
are directed laterally, unlike the ventrally directed processes in
Mamenchisaurus and Euhelopus.
The forelimb was found 1.1 kilometers from the
holotype in the same horizon, so it may not belong to the species.
The humerus is incredibly robust, more so than any
other sauropod I know of. The proximal and distal ends are greatly
expanded and the proximal end is badly preserved. The radius is slightly
bowed and has an expanded proximal end (32% of length). There is a
concavity distally for the carpals. The ulna is straight and greatly
expanded proximally, though the olecranon process is poorly developed and the
proximal edge is not concave. One carpal is present. It is round and
articulates with metacarpals I-III. The metacarpals are preserved in
articulation, which shows they were columnar but lack long intermetacarpal
articulations. Metacarpal I is only 45% of metacarpal III in length and
48% of metacarpal IV in length, while metacarpal III is 42% of the
radius. Metacarpal V is 76% of metacarpal III in length. The manual
phalangeal formula is reduced to 2-2-2-1-1. There is a large ungual on
digit I.
Relationships-
Dong referred this species to the Mamenchisauridae
based on the low neural spine and shallow bifurcation. As explained in my
post on Mamenchisaurus? youngi, the phylogenetic position of Mamenchisaurus is
currently controversial. Both Sereno and Wilson (1998) and Upchurch (1998)
believe the genus is not neosauropod. However, they disagree on whether
Euhelopus and Shunosaurus are closely related to Mamenchisaurus and
Omeisaurus. My analysis of Mamenchisaurus? youngi showed it possessed
some neosauropod and macronarian characters, while lacking others, which
suggested more research is needed but in my opinion strengthened the case for
Euhelopus convergently evolving macronarian-like states.
I provisionally include the teeth and forelimb in
the species Hudiesaurus sinojapanorum because the teeth and forelimb exhibit
characters that would be expected of a non-neosauropod, while the holotype
dorsal vertebra resembles Mamenchisaurus and Euhelopus (both
non-neosauropods)more than other sauropods. The presence of multiple
euhelopodids in the contemporaneous Shangshaximiao Formation and the earlier
Xiashaximiao Formation demands caution in this area however.
Hudiesaurus is more derived than Shunosaurus in
Sereno and Wilson's phylogeny based on the opisthocoelous anterior dorsal
vertebrae. It lacks the neosauropod character of long intermetacarpal
articulations and the macronarian characters metacarpus more than 45% of radius
length (42%) and metacarpal I subequal in length to metacarpal IV (48%).
It also lacks the somphospondylan character of anterior dorsal neural spines
posterodorsally directed. It is excluded from the Diplodocoidea and
Titanosauria by the spatulate, broad tooth crowns with serrations.
Additional characters that exclude it from titanosaur subgroups include- width
of proximal end of radius less than 33% of radial length (32%); no concave
surface on proximal ulna; ossified distal carpal present; metacarpal I shorter
than metacarpal III (45%); hyposphenes and hypantra present. The presence
of a prespinal lamina (presumedly the lamina described as being median in
position on the anterior surface of the neural spine) is a derived character
only known in titanosauroids and diplodocoids. Based on preliminary
analysis then, Hudiesaurus is not a neosauropod, but is more derived than basal
sauropods without dorsal pleurocoels or opisthocoelous centra. The only
non-neosauropods with bifurcated neural spines are Mamenchisaurus, Abrosaurus,
Nurosaurus and Euhelopus (if the latter isn't a titanosaur). Since
Mamenchisaurus and Euhelopus have opisthocoelous dorsal centra, perhaps
Hudiesaurus is more closely related to them than to Abrosaurus (with
platycoelous or amphicoelous centra). The condition in Nurosaurus is
unknown. Then again, the more basal Omeisaurus has opisthocoelous centra
too, so the situation is complex. In any case, this supports Dong's
conclusion of relationship to Mamenchisaurus. I recommend placing
Hudiesaurus in the Euhelopodidae (as I provisionally prefer Upchurch's
phylogeny; in Sereno and Wilson's phylogeny Hudiesaurus would be a
non-neosauropod member of the Omeisaurus + Neosauropod clade, possibly in a
Mamenchisauridae), more closely related to Mamenchisaurus and Euhelopus (and
probably Abrosaurus and Nurosaurus) than to Shunosaurus, Omeisaurus and
Datousaurus.
Those who want scans of the teeth, vertebra and
forelimb (2.5 pages) contact me offlist. There are figures accompanying
the forelimb, manus and vertebra photos, so details are actually
discernable. I wonder what genus I'll do next.....
Mickey Mortimer
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