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New Deinocheirus specimens found, indicating basal ornithomimosaur

From: Ben Creisler

Now that the embargo on the SVP meeting abstracts has expired a number
of notable items can be mentioned, pending formal scientific papers.

Technical Session IX (Friday, November 1, 2013, 9:30 AM)
LEE, Yuong-Nam, Korea Institute of Geoscience and Mineral Resources, Daejeon,
Korea, Republic of (South); BARSBOLD, Rinchen, Paleontological Center,
Mongolia; CURRIE, Philip, University of Alberta, Edmonton, AB, Canada;
KOBAYASHI, Yoshitsugu, Hokkaido University Museum, Sapporo, Japan; LEE, Hang-
Jae, Korea Institute of Geoscience and Mineral Resources, Daejeon,
Korea, Republic of

The holotype of Deinocheirus mirificus was collected by the
Polish-Mongolian Palaeontological Expedition at Altan Uul III in 1965.
Because the holotype was known mainly on the basis of giant forelimbs
with scapulocoracoids, Deinocheirus has remained one of the most
mysterious dinosaurs. Two new specimens of Deinocheirus were
discovered in the Nemegt Formation of Altan Uul IV in 2006 and Bugin
Tsav in 2009 by members of the Korea-Mongolia International Dinosaur
Expedition (KID). Except for the skull, middle dorsal and most of the
distal caudal vertebrae, the right forelimb, left manus, and both
pedes, the remaining parts of the skeleton (Mongolian Paleontological
Center [MPC]-D 100/127) including a left forelimb clearly identifiable
as Deinocheirus were collected. The humerus (993 mm in length) is
longer than the 938 mm humerus of the holotype. The Altan Uul IV
specimen (MPC-D 100/128) is a subadult Deinocheirus (approximately 72%
of MPC-D 100/127), which consists of post-cervical vertebrae, ilia,
ischia, and hind limbs. Both specimens provide important
paleontological evidence for exact postcranial reconstruction of
Deinocheirus mirificus. Cladistic analysis indicates that Deinocheirus
is a basal member of Ornithomimosauria, but many new unique skeletal
features appear to be quite different from other ornithomimosaurs.
These include extreme pneumaticity of tall, anterodorsally oriented
distal dorsal neural spines (7~8 times taller than centrum height)
with basal webbing, fused sacral neural spines forming a midline plate
of bone that extends dorsally up to 170% of the height of the ilium,
ventrally keeled sacral centra, a well-developed iliotibialis flange,
a posterodorsally projecting posterior iliac blade with a concave
dorsal margin, a steeply raised anterior dorsal margin of the ilium,
an anteriorly inclined brevis shelf, vertically well-separated iliac
blades above the sacrum, an completely enclosed pubic obturator
foramen, triangular pubic boot in distal view, vertical ridges on
anterior and posterior edges of medial surface of the femoral head,
and a robust femur that is longer than tibiotarsus. These features
suggest that Deinocheirus (unlike other ornithomimosaurs) was not a
fast-running animal, but a bulky animal with a heavily built pelvis
and hind limbs. However, the dorsal ribs are tall and relatively
straight, suggesting that the animal was narrow-bodied. A large number
of gastroliths (>1100 ranging from 8 to 87 mm) were collected from the
abdominal region of MPC-D 100/127, suggesting Deinocheirus was an