[D] Enigmosaurus mongoliensis [sG] [T]
Barsbold & Perle, 1983
Cretaceous Late Turonian Coniacian Santonian Campanian
Saurischia Theropoda Tetanurae Coelurosauria Therizinosauroidea Therizinosauridae
Baynshirenskaya Svita, Khar Hötöl, Mongolia
Genus - Typespecies
Incompletely preserved pelvis. Possible Enigmosaurus mongoliensis belongs to Erlikosaurus (Barsbold, 1993) for which the pelvis is unknown.
PST GIN AN MNR no. 100/84; pelvis lacking ilia (only bases are preserved).
Pelvis moderately large. Ilia widely positioned. Anterior iliac blades bent externally, posterior blades reduced, a large cubic process present in the posterior dorsal region. Pubic peduncles of ilium are elongated, [ischial] peduncles are shortened. Pubis reoriented posteroventrally, with elongated, laterally narrow, but not flattened shaft. Distal end of pubis elongated and shoe-shaped, narrowed anteriorly and posteriorly. Presymphyseal region of distal end with wide longitudinal (sagittal) indentation that continues onto the anterior portion of the shaft. Ischium parallel to pubis, slightly shorter, and with a narrow shaft. Obturator process displaced distally, elongated, highly narrowed, fuses tightly to the pubis, and is considerably higher than the distal end. Posterior edge of ischium has a weak longitudinal process across from the obturator process. Trochanteric fossa is large, with open edges. No more than six sacral vertebrae present, with highly elongate transverse processes.
Similar features in the pelvis of enigmosaurids and segnosaurids include the following: elongated anterior and posterior [iliac blades] (basic indications of altilia), development of a large shoe-like process on the posterior [distal pubis], widely positioned [ilia] with an outward curvature, highly elongated sacral transverse processes, orientation of the pubes (opisthopuby), and the distal position of the obturator process.
These features support a single type of construction for both pelvic structures. Differentiating features of the pelvis of Enigmosaurus include the absence of lateral flattening of the pubis and ischium, and the entirely different construction and shape of the distal end of the pubis; highly unique characteristics include the considerable narrowing of the anterior and posterior part of the distal pubis, the longitudinally widened indentation in the presymphyseal region of the anterior shaft and the dorsal edge of the distal end; the highly narrowed and elongated obturator process is also characteristic.
The noted features of the pelvis of Enigmosaurus in many ways sharply distinguish it not only from segnosaurids, but also from other theropods. The differences in the pelvis of Enigmosaurus are entirely sufficient to warrant its classification within an independent taxon of family rank. It has been suggested that the studied pelvis may belong to an erlicosaurid, because this structure is unknown so far. It is difficult to deny such a possibility, however the established similarity between Segnosaurus and Erlikosaurus is so great that it does not permit considering the presence of a different pelvic construction among them.
Source: Polyglot Paleontologist
Enigmosaurus mongoliensis is characterized by an uncompressed, narrow pubic shaft and a small and shallow obturator process on the ischium.
Comments by Mickey Mortimer
\\\\\\\"Mongolian mysterious lizard\\\\\\\" Turonian-Campanian, LC Baynshirenskaya Formation, Mongolia.
(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.
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.
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.
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).
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