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This was requested by Dan Bensen.
Enjoy.
Nanshiungosaurus Dong 1979
N. bohlini Dong and Yu 1997
Etymology- "Bohlin's Nanshiung lizard", Dr. Bohlin
being a paleontologist who collected dinosaur remains in Gansu Province, and
Nanshiung being the area the type species was found in.
Barremian, Early Cretaceous
Upper Xinminbao Group, Gansu, China
Holotype- (IVPP V 11116) (5.8-7.8 m) atlas, axis
(148 mm), third cervical vertebra (146 mm), fourth cervical vertebra (161 mm),
fifth cervical vertebra (163 mm), sixth cervical vertebra (164 mm), seventh
cervical vertebra (183 mm), eighth cervical vertebra (183 mm), ninth cervical
vertebra (184 mm), tenth cervical vertebra (183 mm), eleventh cervical vertebra,
cervical ribs, first dorsal vertebra (124 mm), second dorsal vertebra, third
dorsal vertebra, fourth dorsal vertebra, fragmentary dorsal ribs
Diagnosis- eleven cervical vertebrae. Also, it is
the only segnosaur known with fused cervical ribs and dorsal pleurocoels, which
can distinguish it from Alxasaurus and Nanshiungosaurus
brevispinus.
Description-
The description was originally in English, so it's
much more useful than those in Dong 1973. That said, the photograph
quality still leaves much to be desired. This specimen was between 5.8 and
7.8 meters long, comparing the vertebral lengths with Alxasaurus. The
upper limit is close to the size of Therizinosaurus, so this is indeed one of
the largest segnosaurs, as mentioned by Dong and Yu.
The atlas is represented by an odontoid and the
neuropophyses. The odontoid is subcircular and fused to the dorsal half of
the axial centrum. The neuropophysis is apparently wing-like in proximal
view and has a long sauropod-like posterior process. It is unfortunately
not figured.
The axis has relatively long prezygopophyses and
well-developed dorsomedially inclined postzygopophyses. The neural arch
and spine are long and low.
The postaxial cervical vertebrae have elongate
platycoelous centra with pleurocoels. Ventrally, there are two parallel
ridges. The neural arches are low, long and massive with long, stout
zygopophyses, while the neural spines are also long and low. Three laminae
form the diapophyses, which are declined and fused to the cervical ribs.
The parapophyses are large rounded cavities on the anterolateral surface.
The internal structure of the cervical vertebrae is cancellous. Dong and
Yu find that there are eleven cervical vertebrae, one or two more than other
theropods but one less than Dong described for Nanshiungosaurus
brevispinus.
The cervical ribs are fused with their respective
centra.
The dorsal vertebrae have amphiplatyan centra with
ventral keels. The keel is poorly developed on the first centrum.
Large pleurocoels are present. The zygopophyses are long and stout, while
the neural arches and spines are low and narrow.
The dorsal ribs are undescribed.
Note: Dong and Yu list different lengths for
vertebral centra in the text than they do in the measurement table. In the text,
the axis is 152 mm, the seventh and eighth cervicals are 192 mm and the ninth
and tenth are 143 mm. They also later state the dorsals are platycoelous,
instead of amphiplatyan.
Relationships-
It should be noted that Dong and Yu place
segnosaurs in the Segnosaurischia and divide them between the Segnosauridae and
the newly formed Nanshiungosauridae, based on whether they are theropod-like or
sauropod-like. I prefer a division of segnosaurs into Beipiaosaurus and
therizinosauroids, and therizinosauroids into Alxasaurus and
therizinosaurids.
Nanshiungosaurus belongs to the
oviraptorosaur-segnosaur group (which desperately needs a name!) based on the
ventral sulcus on cervical centra delimited by ventrolaterally directed
ridges. The cervical vertebrae resemble other segnosaurs in basic
morphological features such as the long low centra with long, heavy diapophyses
and low neural spines. In addition, oviraptorosaurs lack fused cervical
ribs and among theropods, only Nanshiungosaurus brevispinus is known to have
more than ten cervical vertebrae. Comparison to other segnosaurs is difficult due to the fact that only
Beipiaosaurus, Alxasaurus, Erlikosaurus, Nanshiungosaurus brevispinus and
Segnosaurus are known from presacral vertebrae, and only Alxasaurus is well
described. The cervical centra are platycoelous, like Erlikosaurus and
Segnosaurus, but unlike the amphiplatyan condition in Alxasaurus or the
amphicoelous and opisthocoelous condition in Nanshiungosaurus brevispinus.
Which state is derived is difficult to determine, as Caudipteryx has
amphicoelous centra, Microvenator has platycoelous centra and the Morrison
oviraptorosaur-segnosaur has opisthocoelous centra. Fused cervical ribs
are present, like Erlikosaurus, Nanshiungosaurus
brevispinus and Segnosaurus, but unlike Alxasaurus. Nanshiungosaurus bohlini is like Beipiaosaurus and more basal
than Alxasaurus and Nanshiungosaurus brevispinus based on the presence of dorsal
pleurocoels. The low dorsal neural spines resemble Nanshiungosaurus
brevispinus more than Alxasaurus. Nanshiungosaurus bohlini is also
supposed to be distinguished from N. brevispinus by the narrower dorsal neural
spines. It would appear that Alxasaurus also has narrower dorsal neural
spines than Nanshiungosaurus brevispinus.
Exactly where Nanshiungosaurus bohlini should be
placed within the Segnosauria is hard to say. The presence of fused
cervical ribs and low dorsal neural spines would suggest placement in the
Therizinosauridae, while the presence of dorsal pleurocoels would argue against
placement in the Therizinosauroidea. Thus, placement in the
Therizinosauridae is slightly better supported. For now, I recommend
assigning it to Segnosauria incertae sedis.
Should this species be included in the genus
Nanshiungosaurus? Several facts argue against such an assignment.
First, the presence of dorsal pleurocoels is distinctly more plesiomorphic than
Nanshiungosaurus brevispinus, which shares the derived state with Alxasaurus and
presumedly other therizinosaurids. Second, the cervical morphology is more
similar to Segnosaurus and Erlikosaurus than Nanshiungosaurus brevispinus.
Third, no shared derived characters have been found in both species besides more
than ten cervical vertebrae and low dorsal neural spines, which are currently
unknown in other therizinosaurids. No synapomorphies were suggested by
Dong and Yu. Fourth, the temporal distance is rather great. The
Xinminbao Group has recently been shown to be Barremian, which is much earlier
than the Maastrichtian sediments Nanshiungosaurus brevispinus was found
in. I prefer to refer to this species as "Nanshiungosaurus"
bohlini.
Those of you who want scans of the two figures
(cervical series in ventral view, cervical ten in dorsal and ventral views; 1.5
pages), contact me offlist. Next, I think I'll do Hudiesaurus. I
have a lot of potential dinosaurs to describe, all the Silk Road species,
Isanosaurus, Charonosaurus, Nanshiungosaurus, Shanshanosaurus, etc. If
anyone has a preference out of those species listed, just tell me.
Mickey Mortimer
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