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Details on Enigmosaurus



Yes, I know this is not a particularily recently discovered dinosaur, but
Dan Bensen asked for it, so here it is:

Enigmosaurus Barsbold and Perle 1983
E. mongoliensis Barsbold and Perle 1983
etymology- "Mongolian mysterious lizard"
Turonian-Campanian, LC
Baynshirenskaya Formation, Mongolia
holotype- (GI 100/84) (~5 m) ventral ilium (~650 mm), pubis (634 mm),
ischium (524 mm)
note- Currie and Eberth (1993) suggested that a few elements from the Iren
Dabasu Formation (Coniacian-Campanian) may be referable to Enigmosaurus.
Diagnosis- prominent, ventrally projected pubic peduncle of ilium; pubic
foot consisting of narrow pointed anterior and posterior processes, the
anterior being much longer; long narrow obturator process fused with pubis.
Description-
This therizinosaur was first described and illustrated in Barsbold and Perle
1980 as Segnosaurian indet..  It was later named in 1983.
No more than six sacral vertebrae were present, with elongate sacral ribs.
The ilia are only preserved ventrally and were broadly separated from each
other, with the preacetabular processes deflected laterally.  A lateral
postacetabular tubercle was present, as in Segnosaurus and Alxasaurus.  The
pubic peduncle is thicker and projected more ventrally than Segnosaurus or
Nanshiungosaurus, as in Alxasaurus.
The pubic shaft is laterally narrow, but not compressed, unlike Segnosaurus.
The pubic shafts are said to be separated by a "deep, longitudinal
depression" that continues onto the "anterior portion of the shaft".  The
puboischial contact is narrow as in Segnosaurus, unlike Nanshiungosaurus.
The pubic foot projects into narrow pointed anterior and posterior feet, the
anterior being much larger.  This differs from Segnosaurus, which only has
an anterior foot that is much thicker and blunter.
There is a larger puboischial fenestra than Segnosaurus or Nanshiungosaurus.
The obturator process is narrower and longer than these two genera and is
fused tightly with the pubis.  There is a posterodistal ischial process
across from the obturator process, like Segnosaurus, but the distal ischium
is pointed, unlike that genus.
Relationships-
Barsbold and Perle placed this species in the Segnosauria, but separated it
from Segnosaurus and Erlikosaurus in a separate family- the Enigmosauridae.
This was based on several of the features noted above, which at the time
simply distinguished it from Segnosaurus.  This was because the pelvis of
Erlikosaurus is unknown.  Enigmosaurus could always be the pelvis of
Erlikosaurus, but Barsbold and Perle claimed that Segnosaurus and
Erlikosaurus were too similar otherwise to have such different pelves.  I
disagree, but can not prove the two are synonymous.
As for where in the Segnosauria Enigmosaurus fits, assuming it's not
synonymous with Erlikosaurus, it's hard to tell.  It's obviously more
advanced than Beipiaosaurus and would seem to have a more reduced
postacetabular process than Alxasaurus, so is probably a therizinosaurid.
Curiously, the ischia of Alxasaurus are flattened, a derived character
shared with Segnosaurus, but not Beipiaosaurus or Enigmosaurus.  Then again,
the identification of these elements (in Alxasaurus) as ischia was tenuous
at best, so that may not mean much.  If the ischia of Alxasaurus are
restored correctly, which isn't certain, Enigmosaurus is definately more
derived than it and grouped with Segnosaurus and Nanshiungosaurus based on
the distally placed obturator process and posterodistal ischial process
(shared with Segnosaurus at least).
references-
Barsbold and Perle, 1980. Segnosauria, a new infraorder of carnivorous
dinosaurs. Acta Palaeontologica Polonica, 25(2) 187-195.
Barsbold, 1983. Carnivorous dinosaurs from the Cretaceous of Mongolia.
Transactions of the Joint Soviet-Mongolian Palaeontological Expedition, 19
117 pages.
Currie and Eberth, 1993. Palaeontology, sedimentology and palaeoecology of
the Iren Dabasu Formation (Upper Cretaceous), Inner Mongolia, People's
Republic of China. Cretaceous Research. 14 127-144

I'm pretty sure everyone has a picture of Enigmosaurus's pelvis (the only
figure ever drawn of it), so unless someone specifically asks for it, I
won't bother scanning it.  If you want it though, feel free to ask.

Mickey Mortimer