Included taxa. Deinocheirus mirificus Osmólska and Roniewicz, 1969; Garudimimus brevipes Barsbold, 1981; Harpymimus okladnikovi Barsbold and Perle, 1984; Pelecanimimus polyodon Pérez-Moreno, Sanz, Buscalioni, Moratalla, Ortega and Rasskin-Gutman, 1994. Ornithomimidae Marsh, 1890: Anserimimus planinychus Barsbold, 1988; Archaeornithomimus asiaticus (Gilmoje, 1933); Dromiceiomimus brevitertius (Parks, 1926); Dromiceiomimus samueli (Parks, 1928); Gallimimus bullatus Osmólska, Roniewicz and Barsbold, 1972; Ornithomimus edmontonicus Sternberg, 1933; Ornithomimus velox Marsh, 1890; Struthiomimus altus (Lambe, 1902).

Temporal range. ?Hauterivian-Maastrichtian.

Occurrence. Nemegt Formation, Omnogov, Mongolia; Baynshiren Svita, Omnogov, Mongolia; Shinekhuduk Svita, Dundgov, Mongolia; Calizas de La Huérguina Formation, Cuenca, Spain; Nemegt Svita, Bayankhongor, Mongolia; Iren Dabasu Formation, Nei Mongol Zizhiqu, China; Horseshoe Canyon Formation, Alberta, Canada; Judith River Formation, Alberta, Canada; Denver Formation, Colorado, USA; Kaiparowits Formation, Utah, USA.

Diagnosis. Maxilla excluded from external nares by broad posterior ascending process of the premaxilla (this is a reversal to the ancestral dinosaurian condition, convergently present in Herrerasaurus ischigualastensis', condition unknown in Harpymimus okladnikovi)', humerus long, slender and straight; manual unguals only slightly curved or straight, with reduced, distally placed flexor tubercles; obturator process on ischium is small, triangular and placed entirely on the uppermost fifth of the ischial shaft (unknown in H. okladnikovi and P. polyodon)', pedal unguals ventrally flattened, with a semicircular depression instead of a flexor tubercle.

Remarks. Orn ithomimids (Text-fig. 6e) have long been recognized as a monophyletic clade of theropods (e.g. Marsh 1890; Osborn 1916; Russell 1972; Barsbold 1976 Óz; Barsbold and Osmólska 1990). However, the discovery of primitive forms intermediate between o rnithomimids and other theropods during the last 25 years (Barsbold 1981; Barsbold and Perle 1984; Pérez-Moreno et al. 1994) makes a formal diagnosis of this group more problematic, since several characters that were usually used to define o rnithomimids (e.g. Russell 1972) are absent from these more primitive forms or convergently present in other theropods.

Deinocheirus mirificus has repeatedly been compared with, or even referred to, the Ornithomimosauria (Ostrom 1972; Gauthier 1986; Paul 1988a), but it was listed as a theropod of uncertain taxonomic position by Norman (1990 a). However, the differences between ornit homimids and Deinocheirus listed by Nicholls and Russell (1985) all represent plesiomorphies in the latter taxon, and might, therefore, only indicate that Deinocheirus is not a member of the most advanced ornithomimosaurs, the ornithomimids. D. mirificus shares with all ornithomimosaurs the apomorphic presence of an especially long, slender and straight humerus, and with all members of this clade which are more derived than Harpymimus the apomorphic characters of the first metacarpal being subequal in length to metacarpal II, and the presence of a reduced, proximally placed, triangular deltopectoral crest on the humerus. Therefore, the taxon is referred to the Ornithomimosauria here.

Even after the inclusion of the more primitive members, the monophyly of the o rnithomimo saurs is still well supported by apomorphic characters (see above); therefore, they are treated as a single OTU. The phylogenetic relationships within ornithomimosaurs are probably (Harpymimus (Pelecanimimus,? Deinocheirus (Garudimimus, O rnithomimidae))) (modified from Barsbold and Osmólska 1990).