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The Most Ancient Ornithomimosaur (Theropoda, Dinosauria)

 INTRODUCTION
The infraorder Ornithomimosauria differs from
other carnivorous dinosaurs (Theropoda) in the short
postorbital and elongated preorbital parts of a rela
tively small head, preservation of the prefrontals, and
the maxillae excluded from framing the nares. The
teeth, if present, are small and lack a serrated border.
In the postcranial skeleton, the cervical vertebral
region is elongated, the pelvis is prepubic, the manus
is large, the separate first and second distal carpals,
usually elongated metacarpals I, and metacarpals II
and III are equal in size. The majority of ornithomi
mosaurs have a compact foot, so that in the most spe
cialized case, an arctometatarsal pattern is developed.
Ornithomimosaurs are most abundant and most
diverse in North America and Central Asia. In North
America, all known specimens belong to three genera
(Struthiomimus, Ornithomimus, Dromiceomimus) of
the family Ornithomimidae. All of them dwelt at the
end of the Late Cretaceous, beginning from the latter
half of the Campanian. In Asia, the most ancient orni
thomimid remains come from the Tokubai Formation
(Lower Cenomanian) of Kyrgyzstan (Ornithomimi
dae indet.: Averianov, 2006) and the latest forms (rep
resented by the species Gallimimus bullatus Osmólska
et al., 1972 and  Anserimimus planinychus Barsbold,
1988) are dated to the Nemegt Formation (Upper
Campanian–?Lower Maastrichtian) in southern
Mongolia. The family has also been recorded in the
first part of the Upper Cretaceous of Tajikistan (Orni
thomimidae indet.: Alifanov and Averianov, 2006) and
northeastern China. The material from China
includes two species:  Sinornithomimosaurus dongi
Kobayashi et Lü, 2003 (represented by a series of com
plete skeletons) and  Archaeornithomimus asiaticus
(Gilmore, 1933).
The Bain Shire Formation (Upper Coniacian–
Lower Santonian) of Mongolia has yielded Garudimi
mus brevipes Barsbold, 1981, represented by a skull
and fragments of postcranial skeleton. This form is
undoubtedly related to typical ornithomimids, but dif
fers from them in certain archaic characters of the
skull (for example, relatively large lower temporal
fenestrae) and postcranial skeleton (for example,
equal length of the femur and shin bones, short meta
tarsus, proarctometatarsal pattern, and preservation of
the first digit of feet). Barsbold (1981) proposed that
G. brevipes belongs to the family Garudimimidae
related to ornithomimids.
The most extraordinary ornithomimosaur
Deinocheirus mirificus Osmólska et Roniewicz, 1969
comes from the Nemegt Formation of Mongolia. This
species was characterized based on bones of the pecto
ral girdle and forelimbs extremely large in size (2.4 m
of total length); it is also distinguished by extensive
coracoids, straightened humeri, triangular deltopec
toral crest of the last, aligned metacarpals, large manus,
and hooked ungual phalanges. In the original descrip
tion (Osmólska and Roniewicz, 1969), D. mirificus was
assigned to a separate family, the Deinocheiridae
dinosaur
 

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