ostrich dinosaurs from the late cretaceous of western canada

Ostrich Dinosaurs from the Late Cretaceous of Western Canada

DALE A. RUSSELL National Museum of Natural Sciences, National Museums o f Canada, Ottawa, Canada

Manuscript received November 3, 1971 Accepted for publication January 18, 1972

The family Ornithomimidae is defined on the basis of the skeletal morphology of the three genera Ornithomimus, Struthiomimus, and Dromiceiomimus known in continental strata in Alberta, which are temporally equivalent to the Upper Campanian substage. At least two genera occur in Canadian Lance (Upper Maestrichtian) equivalent strata, but cannot be identified at present. A group of more primitive ornithomimoid theropods is represented elsewhere by the late Jurassic Elaphrosaurus and early Cretaceous Archaeornithomimus.

Ornithomimid attributes include a general body form which parallels that of the ratites; elongate forelimbs, a kinetic skull, enormous eyes, a relatively highly evolved brain, and possibly a secondary palate and supertemporal fenestrae which were nearly encircled by alae of the squamosal. A reconstruction of the myology of the thigh indicates that ornithomimids were extremely fleet, but lacked the agility characteristic of modern large ground birds. They probably subsisted on small, soft-bodied animals.

Nous nous basons sur trois genres (Ornithomimus, Struthiomimus, Dromiceiomimus) qui proviennent de strates continentales de l'Alberta Bquivalentes en temps au sous-ktage Cam- panien Supkrieur, pour dBfiner la famille des Ornithomimidae. Au moins dew genres qui ne peuvent &tre identifiks pour l'instant se trouvent dans des strates canadiennes kquivalentes B la Formation Lance (Maestrichtien Supkrieur). Un groupe de ThBropodes ornithomimo'ides plus primitifs est reprdsentk ailleurs par le genre Elaphrosaurus de la fin du Jurassique et le genre Archaeornithomimus du dkbut du CrktacC.

Les caractkristiques des Ornithomimidae comprennent: une anatomie gknCrale semblable B celle des Ratites, des membres antkrieurs allongh, un kin&-criine, des yeux Cnormes, un cerveau relativement trks 6volu6, et aussi possiblement, un palais secondaire et des fen&tres supratemporales presque encerclQs par les alae du squamosal. Une reconstitution de la myologie de la cuisse indique que les Ornithomimidae Btaient trhs lestes tout en n'ayant pas l'agilitk caractkristique des gros oiseaw modernes qui vivent au niveau du sol. 11s se nourris- saient probablement de petits animaux sans squelette.

Introduction The ornithomimids, or ostrich dinosaurs,

were highly cursorial theropods which re- sembled modem large ground birds in their general size, powerfully developed hind limbs, long neck, and small edentulous head. Their forelimbs were, however, long and terminated with claws. Remains of these animals are known from Cretaceous sediments in North America and Eurasia.

The cursorial adaptations of ornithomimids were recognized long ago by Osborn (1902, p. 8) , and the hind limb of the generotypic specimen of Ornithomimus was originally compared to that of an ostrich by Marsh ( 1890). Although a few incomplete specimens were found at various localities in North America before the period of intensive collecting began on the Red Deer River in Alberta in 1910, the general morphology of these peculiar forms re-

Canadian Journal of Earth Sciences, 9. 375 (1972)

mained obscure until Osborn ( 191 7) described an essentially complete Struthiomimus skeleton from the Oldman Formation. A summary of the history of classification of the Ornitho- mimidae was given by Gilmore (1920), and both he and Matthew and Brown (1922) characterized the group, largely on the basis of Osborn's magnificent skeleton. A complete but crushed skull of a specimen from the Old- man Formation was described by Parks (1928), and several specimens from the Edmonton Formation were described by Parks (1926, 1933) and Sternberg (1933). Since then our knowledge of ostrich dinosaurs has been largely based on the Alberta material, although several Old World occurrences have been re- corded (see Table I ) , notably by Gilmore (1 933) from the Iren Dabasu Formation of Mongolia, and more recently by Kielan-Jawo- rowska and Dovchin (1969) from the Upper

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376 CANADIAN JOURNAL OF EARTH SCIENCES. VOL. 9, 1972

TABLE 1. Taxa which have been referred to the Ornithomimidae

Original reference Present determination

Coelosaurus antiquus Leidy 1865, p. 100 (Upper Cretaceous, New Jersey)

Ornithomimidorum gen. a lonzeensis (Dollo 1883, p. 213) Huene 1926, p. 87 (Glauconite of Lonzk, Belgium)

Betasuchus bredai (Seeley 1883, p. 246) Huene 1932, p. 70 (Maestricht Tuff Chalk, Holland)

Ornithomimus velox- Marsh 1890, p. 84 (Denver Formation, Colorado)

Ornithomimus tenuis Marsh 1890, p. 85 (Judith River Formation, Montana)

Ornithomimus grandis Marsh 1890, p. 85 (Eagle Sandstone, Montana)

Ornithomimus sedens Marsh 1892, p. 451 (Lance Formation, Wyoming)

Ornithomimus minutus Marsh 1892, p. 452; Gilmore 1920. a I42 ( ?Laramie Formation. Coloradol

~fr~tthio&imw alrus (Lambe 1902, p. 50) 0sbom 191 7, p. 744 (Oldman Formation, Alberta)

Ornii/~omimus afinis Gi lmore 1920, p. 137 (Arundel Formation, Maryland)

Chirostenotes pergracilis GiImore 1 924, p. 3 (Oldman Formation, Alberta)

Oviraptor philoceratops Osborn 1924, p. 7 (Djadochta Formation, Mongolia)

Struthiomimus brevitertius Parks 1926, p. 65 (Edmonton Formation, Alberta)

Struthiomimus samueli Parks 1928, p. 6 (Oldman Formation, Alberta)

Macropl~alangia cattfldensis Sternberg 1932, p. 100 [Oldman Formarlon, Alberta)

Orni~hotnimus edmontonicus Sternberg 1933, p. 79 (Edmonton Formation, Alberta)

Strrrthtomimus currelli Parks 1933, p, 4 (Edmonton Formation, Alberta)

Stru~hiomimus iwens Parks 1 933, p, 13 (Edmonton Formation, Alberta)

Ornifl~omimus elegans Parks I 9 33, p. 16 (Oldman Formation, Alberta)

Ornithomimus asiaticus Gilmore 1933, p. 27 (Iren Dabasu Formation, Mongolia)

Ornithomimoides mobilis Huene and Matley 1933, p. 64 (Lameta Formation, India)

Ornithomimoides barasimlensis Huene and Matley 1933, p. 64 (Lameta Formation, India)

Ornirhomimus sp. Ostrom 1970, p. 67 (Cleverly Formation, Wyoming and Montana)

Ornithomimid (Matthew and Brown 1922, p. 373), nomen dubium

Ornithomimid? nomen dubium

Omithomimid, nomen vanum

Ornithomimus velox

Troijdontid ?

Tyrannosaurid (Osborn 191 7, p. 740)

Ornithomimus sedens

Dromaeosaurid ?, Pterosaur ? nomen dubium

Struthiomimus altus

Archaeornithomimus afinis

Theropod, not ornithomimid


Dromiceiomimus brevitertius

Dromiceiomimus samueli


Ornithomimus edmontonicus

Ornithomimus edmontonicus (Sternberg 1934, p. 7)

Dromiceiomimus brevitertius

Macrophalangia canadensis

Archaeornithomimus asiaticus

Ornithomimid ? nomen vanum

Theropod, nomen vanum

Ornithomimid, genus not determinable at present

Nemegt Beds of Mongolia. The latter material is excellent and is currently being studied by Osmolska and Roniewicz.

Within the borders of the present prairie provinces of Alberta and Saskatchewan the remains of ostrich dinosaurs are found in sediments which were deposited on low, alluvial plains during late Cretaceous time (Upper Campanian and Maestrichtian equivalents). The well-known sequence of interdigitating continental and marine strata begins with the Milk River Formation (which has not yet yielded ornithomimid material; the pedal pha-

lanx described by L. S. Russell 1935, Plate 2, Fig. 10 probably belongs to an immature deinonychosaur) and continues through a section of approximately 1000 m thickness containing, in ascending order, the dinosaur-bearing Oldman, Edmonton, and upper Edmonton For- mations. For a general description of the dinosaur faunas of western Canada see D. A. Russell (1967) and Russell and Chamney (1967), and Dodson (1971) for a study of the taphonomy of the Oldman Formation.

The present review is an attempt to define the Canadian ornithomimid forms, and to com-

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RUSSELL: LATE CRETACE

ment on some of the peculiarities and possible habits of the group. All measurements are in millimeters.

Family Ornithomimidae Marsh 1890

Diagnosis Skull relatively small and edentulous. Maxilla

excluded from external narial border, secondary palate present. Orbit large. Temporal region reduced, alae from squamosal may nearly en- close supratemporal fenestra. With possible exception of anterior cervicals, presacral vertebrae lack pleurocoels. Six centra co-ossified in adults to form sacrum. Distal caudal vertebrae with elongate anterior zygapophyses. Length of humerus greater than half length of femur. Antebrachium elongate, carpalia reduced, and unsuited for extensive mediolateral movement. All 3 metacarpals approximately equal in development. Digits of manus elongate and approximately equal in length. Length of pubic boot less than half Iengih of Femur. Ischia distally expanded and ventrodistally recurved. Pelvic canal broad. Tibia-astragalus longer than femur. MetatarsaI 3 constricted proximally. First phalanx not present in pes, phalanges of fourth digit unusually abbreviated. Pedal unguals ungulate.

Discussion The foregoing diagnosis is based on late

Cretaceous ornithomimoid theropods only. The presence of a secondary palate in the group is indicated by cranial remains preserved with specimens of Struthiomimus and Dromiceiomi- mus, and an unusual anteromedial development of the squamosal is suggested in a well preserved specimen of the latter genus. The morphology of these structures is described below under the appropriate generic headings.

There is some conflict in the literature re- garding the number of sacral vertebrae present in ornithomimids, Gilmore (1920, p. 132; 1933, p. 28) listing 4, and Parks (1926, p. 67; 1933, pp. 8, 13) indicating 6. If vertebrae which are united by their centra into a series, and contact the ilium through either sacral ribs or transverse processes may be regarded as pertaining to the sacrum, then 6 sacral vertebrae are present in ornithomimids.

Sacrals 3 to 5, as defined above, bear sacral ribs in ornithomimids (see Gilmore 1920, Fig.

.OUS OSTRICH DINOSAURS 377

67; 1933, Fig. 2) and are homologues of sacrals 2 to 4 in tyrannosaurids (see Osborn 1917, Fig. 20). It would appear that the "sacral rib" of the first and second sacral vertebrae in ornithomimids, and of the first sacral vertebra in tyrannosaurs (see Osborn 19 17, Figs. 19-20 and NMC 8506) is actually the transverse process of a former dorsal vertebra, as it is in an elevated intravertebral position and is not suturally separated from the neural arch. Accordingly the posterior limit of vertebrae, morphologically derived from the dorsal series, lies between the second and third sacral in ornithomimids, and between the first and second sacral in tyrannosaurids. The pubis and ilium meet anterior to the acetabulum opposite the first sacral vertebra in Allosaurus and tyrannosaurids (corresponding to the second sacral in ornithornimids). In ornithomimids these elements meet opposite the third sacral vertebra, giving the sacrum the appear- ance of having incorporated 2 more dorsal vertebrae into this structure than is the case in tyrannosaurids.

Langston (1960, p. 335) has pointed out that the "transverse processes" of basal caudal vertebrae in hadrosaurs are caudal ribs, as is also the case in sauropods (Marsh 1896, Plate 34). In theropods the transverse processes of these vertebrae are more dorsal in position, arising entirely from the neural arch, and it is not clear whether or not they are homologous with the sacral or caudal ribs. In any event the last sacral vertebra in Allosaurus (Gilmore 1920, Plate 8), tyrannosaurids and ornithomimids seems to have been acquired from the anterior end of the caudal series, leaving the 3 vertebrae anterior to it as the "stem" sacrals.

The dinosaurian specimens which have been collected from the Oldman and Edmonton For- mations of Alberta range in size from the massive, 12 m long hadrosaur Edmontosaurus to the small theropod Stenonychosaurus, which may have measured but 2 m in length. Most of the articulated material from these units pertains to the larger forms, while smaller species are nearly always represented only by isolated teeth and phalanges. Ornithomimids are among the smaller of the dinosaurs, and their skeletons are usually incomplete and disassociated, as well as badly crushed. As a consequence of the small amount of variability

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in the shape of the individual bones, it was necessary to assess the relative proportions of the different skeletal structures in order to distinguish the taxa. It is evident that this combination of factors has not facilitated the study of the group, and it was not possible to identify all of the material.

It has been convenient to introduce two new terms. The "transition point7' between the proximal and distal segments of the tail refers to the point between the last vertebra bearing transverse processes and the first with distinctly elongate prezygapophyses. The length of the "antilium" is measured from the anterior limit of the anteroventral emargination of the ilium to the anterior rim of the acetabulum in the center of the pubic peduncle of the ilium. The following abbreviations of institutional names precede the specimen numbers referred to in the text and identify the place of storage of the specimens: AMNH, American Museum of Natural History; BMNH, British Museum of Natural History; NMC, National Museum of Natural Sciences, National Museums of Can- ada; ROM, Royal Ontario Museum; YPM, Peabody Museum of Natural History, Yale University.

Relationships of the Ornithomimidae The type species of Coelurus, C. fragilis, is

based on an anterior caudal vertebra of a small theropod (YPM 1991, see Lull in Gilmore 1920, p. 127), which has been misidentified in the literature as pertaining to the dorsal region of the vertebral column. The illustrations of this vertebra (Marsh 1896, Plate 7, Figs. 3, 3a, 3b) resemble those of the anterior caudal region of Ornitholestes (Osborn 19 17, Plate 26) but differ from similar vertebrae in ornithomimids in that the centrum is rhomboid in lateral aspect instead of rectangular, and the edges of the central articular facets are more rounded. Whatever their broader relationships were within the Theropods, the ornithomimids probably were not closely allied to Coelurus and the Coeluridae sensu strictu. This intro- duces an element of doubt both into the validity of considering ornithomimids as coelurosaurs, and into the taxonomic meaning of the latter term.

The type of Elaphrosaurus bambergi, from the late Jurassic of Tanzania (Janensch 1925),

bears many suggestions of ornithomimid &n- ity in its morphology (see also Nopcsa 1928, p. 183). Among these are the form of the presacral and anterior caudal vertebrae, the presence of elongated anterior prezygapophyses on the distal caudal vertebrae, absence of a crest on the anteroproximal surface of the pubis and unusually abbreviated phalanges of the fourth toe. Unfortunately, the skull was not preserved. The animal was not as well adapted to a cursorial mode of existence as were the late Cretaceous ornithomimids, as evidenced by the shortness of the ilium and hind limbs relative to the elements of the vertebral column. It is also primitive in possessing a relatively shorter humerus and a dorsally unconstricted third metatarsal. However, there is nothing in the known morphology of Elaphrosaurus which excludes it from the ancestry of the ornithomimids, and the genus probably was more nearly related to them than to Coelurus fragilis.

The pubis of the type of "Coelurus" agilis (see Lull in Gilmore 1920, p. 129, Plate 34, Figs. 5-6) is long (suggesting a cursorial adaptation in the form), lacks a crest on its anteroproximal surface, and the pubic boot is convex ventrally in lateral profile. The morphology of this element is very similar to that of the pubis in ornithomimids and the known morphology of the bone in Elaphrosaurus. The evidence here cited suggests that the species would be better assigned to the African genus than to Coelurus.

Ornithomimid remains are known from only a few early and middle Cretaceous localities. "Ornithomimus" asiaticus, from the Iren Da- basu Formation of Mongolia (Gilmore 1933, p. 27) is more primitive than, and is distinguished from later Canadian forms in the shortness of the first and third metacarpal relative to the second (AMNH 6569), and the shortness of the metatarsals relative to their midshaft circumference (the circumference of the fourth metatarsal of AMNH 6565 "0." asiaticus equals 25.9% of the length of the bone, while in AMNH 5375 Struthiomimus altus this ratio amounts to 20.6%). If all of the disassociated ornithomimid material from this locality belongs to a single species, the form may be further characterized by straight manal unguals, as in Ornithomimus edmontonicus, and recurved pedal unguals. "Ornithomimus"

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RUSSELL: LATE CRETACEOUS OSTRICH DINOSAURS 379

asiaticus is here designated as the type species of the new genus Archaeornithomimus.

"Ornithomimus" afinis, from the Arundel Formation of New Jersey (Gilmore 1920, p. 137), is also known from scattered and incomplete material. Due to the recurved nature of the pedal unguals, the species is referred to A rchaeornithomimus.

A distinct lineage of ornithomimoid theropods was therefore already established by late Jurassic time. The evolutionary history of the group seems to be characterized by the development of progressively more perfect cursorial adaptations. Although the morphological diversity in the group has been only very incompletely sampled, it is possible that the stringent physical requirements imposed on the organisms by the need for rapid locomotion may have tended to limit their general body form to an approximately uniform, but efficient morphology, as is the case with flight in birds.

Genus Ornithomimus Marsh 1890, p. 84

Diagnosis (based on 0 . edmontonicus) Length of presacral vertebral column less

than combined lengths of femur, tibia-astragalus, and third metatarsal. Tail incompletely known. Humerus longer than scapula. Antebrachium about half as long as femur, lightly constructed. First metacarpal longer than metacarpals 2 and 3, manus digits subequal in length; manus unguals subequal in length, neither heavily recurved nor powerfully constructed. Ungual of third digit of manus shorter than penultimate phalanx of third digit. Antilium relative to femur longer than in Struthiomimus, shorter than in Dromiceiomimus. Tibia and metatarsus shorter relative to femur than in Struthiomimus and Dromiceiomimus.

Discussion The generotypic species of Ornithomimus

( 0 . velox) was founded on broken elements of the distal region of a left hind limb (YPM 542) from the latest Cretaceous Denver For- mation of Colorado (see Osborn 1917, pp. 738-740 for a description of the type locality). As reconstructed by Marsh ( 1890, Plate 1) and followed by later authors, the metatarsus is unique among ornithomimids in its shortness and in that the second metatarsal

is longer than the fourth. Osborn (1917, p. 743), supposing the fourth metatarsal lacked a facet for articulating with the splint-like, fifth metatarsal, firmly asserted that the latter element was absent in 0 . velox. In fact, metatarsal 4 does bear a small, polished articular facet proximolaterally (see also Ostrom 1970, p. 68) and there are no contacts between distal and proximal fragments of any metatarsal in the pes. The metatarsus of 0. velox is therefore not known to differ significantly from the usual morphology of this structure in ornithomimids.

Three metacarpals (YPM 548) were dis- covered near the remains of the hind foot. Marsh (1890, p. 85) stated that, with the exception of their small size, ". . . there is no reason why they do not pertain to the same specimen as the hind foot." The ratio between the lengths of the first metacarpal (YPM 548) and the first phalanx of the second digit of the pes (YPM 542) equals approximately 107% (see Osborn 1917, Fig. 3a, A-B), while the same ratio in the type of 0. edmontonicus amounts to approximately 108%. The metacarpus (YPM 548) is therefore here considered to belong to the type specimen of 0 . velox. It is because of the similarly greater length of the first metacarpal relative to the lengths of the other metacarpals in 0. velox that 0. edmontonicus is referred to Ornithomimus.

The type of Ornithomimus sedens from the Lance Formation of Wyoming consists of most of the sacrum and adjoining pelvic arches, and basal caudal vertebrae. It has been well described by Gilmore (1920, pp. 13 1-1 35). The type material is not complete enough to permit the species to be assigned with certainty to any one of the 3 genera here recognized in the late Cretaceous of North America. The ratios of the posterior width of the centra of the basal caudal vertebrae to their central lengths are approximately intermediate between those of comparable vertebrae of Dromiceiomimus (NMC 12228) and Struthiomimus (NMC 8902). It should be noted that of the 14 "specimens" listed by Osborn (1917, p. 741 ) from the Hell Creek Formation of Montana, only 6 contain fragmentary ornithomimid material (AMNH 1006, 5003, 5016, 5017, 5018, 5051; AMNH 974 and 975 could not be located in the collections), none of which is generically determinable.

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RUSSELL: LATE CRETACEOUS OSTRICH DINOSAURS

TABLE 2. Ornithomimus edmontonicus, length of skeletal elements

ROM 851

(% of femur length) NMC 12441

skull cervical vertebrae cervicals 4-10 12 dorsal vertebrae dorsals 1-7 sacrum 12 basal caudal vertebrae scapula humerus ulna metacarpal I metacarpal I1 metacarpal I11 phalanx 1-1 (manus) phalanx 1-2 phalanx 11-1 phalanx 11-2 phalanx 11-3 phalanx 111-1 phalanx 111-2 phalanx 111-3 phalanx 111-4 digit I1 manus ilium antilium femur tibia-astragalus metatarsus digit 111, pes

+The tibia is 538mm long, and the axial length

Ornithornimus edmontonicus Sternberg 1933 Ornithomimus edmontonicus Sternberg 1933,

p. 79. Struthiomimus currelli Parks 1933, p. 4.

Distribution Oldman Formation, member A of Edmonton Formation, Red Deer River, Alberta.

Type NMC 8632, fragments of three vertebrae, dorsal and abdominal ribs, proximal ends of both scapulae, both coracoida and humeri, right forelimb, distal end of left femur, both tibiae-fibulae, right and part of left pes (section 34 township 30 range 21 west of the Fourth meridian, approximately 30 m above the west bank of the Red Deer River, member A of the Edmonton Formation).

Referred Specimens ROM 851 (type of Ornithomimus currelli) , skeleton lacking tail, distal end of left tibia and left pes (?section 10 township 30 range 21 west of the Fourth meridian, approximately 30 m above the east

I of the astragalus is estimated to have been 14mm.

bank of the Red Deer River, member A of the Edmonton Formation).

NMC 12441, several dorsal ribs and caudal vertebrae, left humerus, both radii-ulnae, several metacarpals and phalanges, both femora and tibiae-fibulae (2.4 km south of Steveville ferry crossing, Dinosaur Provincial Park).

Discussion It is not possible to separate Or- nithomimus edmontonicus (see Plate 1 ) from 0. velox on the basis of existing materials. However, because the former species occurs in pre-Lancian sediments in Alberta and the type of 0. velox was taken from Lance-equivalent strata in Colorado, the possibility exists that new material may show them to be distinct. Sternberg (1934) demonstrated that "Struthio- mimus" currelli is a junior synonym of Ornitho- mimus edmontonicus. Two specimens of this form have been described in detail by Stern- berg (1933) and Parks (1933), from the Edmonton Formation. A third and larger individual documents the presence of the species in the Oldman Formation (NMC 12441, for

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measurements see Table 2). There seem to be no taxonomically significant morphological differences between this specimen and those of the younger Edmonton Formation.

The skull of ROM 851 has been crushed to a thickness of only 33 mm. Because of this and the incompleteness or damaged condition of other ornithomimid skulls from the late Cre- taceous of North America, it is difficult to distinguish 0. edmontonicus from other taxa on the basis of cranial characters. The supratemporal fenestra is not bridged by a bar of bone, as was suggested by Parks (1933, p. 6). This fenestra is very small, measuring only 9 mm in a longitudinal direction. In a skull of a contemporary Dromiceiomimus of comparable size (NMC 12228) the supratemporal fenestra has a length of 25 mm. The dorsal surface of the nasals in ROM 851 and ROM 1790 (Struthiomimus altus) bears small pits and grooves, reminiscent of the warty appear- ance of this bone in tyrannosaurs.

Ornithomimus edmontonicus differs from Struthiomimus in the shorter length of the presacral vertebral column relative to the combined lengths of the femur, crus, and metatarsus, and resembles Dromiceiomimus in this regard. However, in the latter genus the crus and metatarsus are longer relative to the femur than in 0. edmontonicus. The morphology of the tail is unknown in 0. edmontonicus, except for 4 distal caudal vertebrae associated with NMC 1244 1. These are similar to corresponding elements of Struthiomimus and Dromiceio- mimus.

The bones of the anterior limb of 0. edmontonicus are as long relative to the length of the femur as are those of Struthiomimus, but are much more lightly constructed. For example, the ulna of NMC 12441 ( 0 . edmontonicus) is similar to that of NMC 8902 (S. altus) in length, but its midshift diameter is 11.6 mm and that of the latter specimen measures 19.5 mm. Comparable diameters of the humeral shaft in these specimens measure 29.6 and 41.0 mm respectively. The anterior limbs of ROM 851 are peculiar in that the left antebrachium is unusually short (Parks 1933, p. 9) , and a small splint of bone (29 mm in length) is present articulating with the proximo- internal surface of the right first metacarpal (Parks 1933, Plate 3, Fig. 1 ) .

Genus Struthiomirnus Osborn 1917, p. 744 Diagnosis Length of presacral vertebral column more than combined lengths of femur, tibia-astragalus and third metatarsal. Posterior width of anteriormost 15 caudal centra greater than half of central length, transition point b e tween proximal and distal segments of tail occurs between caudals 15 and 16. Humerus shorter than scapula. Antebrachium about half as long as femur, powerfully constructed. First metacarpal shorter than metacarpals 2 and 3, manus digits unequal in length, manus unguals unequal in length, heavily recurved and powerfully constructed. Ungual of third digit of manus longer than penultimate phalanx of third digit. Antilium, tibia, metatarsus, and digit 3 of pes shorter relative to femur than in Dromiceiomimus.

Discussion Ornithomimus altus was based (Lambe 1902, p. 50) on a fragmentary specimen from the Oldman Formation. Osborn ( 19 17) later referred a nearly complete skeleton (AMNH 5339) to this species, and placed it in the genus Struthiomimus. The sole morphological justification Osborn cited for erect- ing this new genus was the presence of a rudimentary fifth metatarsal, which was supposedly absent in the more progressive Ornithomimus velox. Realizing that Osborn had insufficiently distinguished the two genera, Gilmore ( 1920, p. 130) regarded Struthiomimus as a junior synonym of Marsh's genus, as have most later authors. Sternberg (1933, p. 79), however, provisionally recognized Struthiornimus as a valid genus in the expectation that additional material of Ornithomimus velox would show it to be generically distinct from S. altus.

The type specimen of S. altus is virtually undeterminable. The length of the femur as given by Lambe (1902, p. 53, the bone has since been irrepairably damaged) is probably about 25 mm too short relative to the actual lengths of the pedal phalanges of the same specimen, and too long by about the same amount relative to the lengths of the pedal phalanges of a Dromiceiomimus specimen of similar size (ROM 852). If the femur were originally 25 mm longer, the ratio of the lengths of the fourth metatarsal and the femur would correspond closely to the same ratio in Osborn's specimen (AMNH 5339, 72.5% ) .

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RUSSELL: LATE CRETACEt

Other considerations suggesting that the type of S. altus and AMNH 5339 may belong to the same species are a somewhat greater proximal depth of the second phalanx of the second pedal digit relative to its length than is usual in other ornithomimid forms occurring in the Old- man Formation, and the fact that specimens of the AMNH 5339 species are more abundant in the Oldman Formation than are those of other forms. From a nomenclatural point of view it is fortunate that Osborn's referral of AMNH 5339 to Lambe's species seems to have been correct. Assuming then that Ornithomimus has been correctly defined in this paper, Struthio- mimus can be separated easily from that genus on the basis of the foregoing diagnosis.

Struthiomimus altus (Lambe 1902) Osborn 1917

Ornithomimus altus Lambe 1902, p. 50. Struthiomimus altus Osborn 19 17, p. 744.

Distribution Oldman Formation, member B of Edmonton Formation, Red Deer River, Alberta.

Type NMC 930, distal ends of pubes and ischia, right hind limb, phalanges of left pes (Oldman Formation, probably near Steveville ferry crossing, Dinosaur Provincial Park).

Referred specimens AMNH 5257, three caudal vertebrae, both scapulae-coracoida and humeri, left radius-ulna, right metacarpus, right ilium, both ischia and pubes, right hind limb, left femur (?section 18, township 32, range 21, west of Fourth meridian, approximately 12 m above the west bank of the Red Deer River, member B of the Edmonton Formation).

AMNH 5339, complete skeleton, lacking only skull roof and distal end of tail (Oldman, Formation, basin of Little Sandhill Creek, Dinosaur Provincial Park).

AMNH 5355, left frontal, posterior half of braincase, atlas, 10 additional presacral and 8 caudal vertebrae, right scapula-coracoid, right crus and calcaneum-astragalus (basin of Little Sandhill Creek, Dinosaur Provincial Park).

AMNH 5375, two manus phalanges, left and distal end of right femur, right fourth meta-

3US OSTRICH DINOSAURS 383

tarsal, distal ends of both second and left third and fourth metatarsals, 4 pedal phalanges (basin of Little Sandhill Creek, Dinosaur Pro- vincial Park).

AMNH 5385, caudal vertebra, distal ends of ischia, both tibiae-astragali, right fibula, distal ends of left metatarsus, 5 pedal phalanges (basin of Little Sandhill Creek, Dinosaur Pro- vincial Park).

AMNH 5421, sacrum and adjacent dorsal and caudal vertebrae, left humerus, both radii- ulnae, pelvis, right hind limb, left femur and tibia-fibula (basin of Little Sandhill Creek, Oldman Formation, Dinosaur Provincial Park).

NMC 8897, sacrum and ilia, distal ends of pubes and ischia, proximal end left femur (4.75 km southeast of mouth of Little Sand- hill Creek, Oldman Formation, Dinosaur Pro- vincial Park).

NMC 8902, incomplete axial skeleton, left scapula-coracoid, right humerus, left ulna, left and fragment of right ilium, distal ends of pubes, proximal end left femur (2.4 km east of mouth of Little Sandhill Creek, section 8, township 21, range 11, west of Fourth meridian, near middle of exposures, Oldman For- mation, Dinosaur Provincial Park).

ROM 1790, preorbital region of skull, both dentaries, sacrum and adjacent dorsal and caudal vertebrae, pelvis, both femora and tibiae-fibula, left pes (quarry 18 of Sternberg 1950, Oldman Formation, Dinosaur Provincial Park).

Discussion Our knowledge of Struthiomimus altus (Fig. 1) is based on a series of well preserved specimens from the Oldman Formation, and one individual (AMNH 5257, for measurements see Table 3 ) exhibiting diagnostic char- acteristics of the species from the Edmonton Formation. The specimen excellently figured and described by Osborn (1 9 17, AMNH 5339) is by far the finest ornithomimid skeleton ever collected from North America, both in com- pleteness and in excellence of preservation. It has been remeasured in some detail (Table 3).

Cranial remains of AMNH 5339 have been figured by Osborn ( 191 7, Fig. 5a), and small fragments of the otic region of the braincase of this specimen were also collected. A poorly

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CANADIAN JOURNAL OF EARTH SCIENCES. VOL. 9, 1972

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TABLE 3. Struthiomimus altus, length of skeletal elements

AMNH 5339

(% of (mm) femur length) AMNH 5257

-

skull 2AO+ 50 cervical vertebrae 71 5 149 cervicals 4-10 586 122 12 dorsal vertebrae 761 + 159 dorsals 1-7 - - sacrum 390 81 12 basal caudal vertebrae 750 156 scapula 3 50 73 humerus 310 65 ulna 246 5 1 radius 228 48 metacarpal I 89 19 metacarpal I1 103 21 metacarpal 111 103 21 phalanx 1-1 (manus) 114 24 phalanx 1-2 85+ + 18 phalanx 11-1 44 9 phalanx 11-2 89 19 phalanx 11-3 100+ + 21 phalanx 111-1 28 6 phalanx 111-2 28 6 phalanx 111-3 68 14 phalanx 111-4 87+ + 18 digit I1 manus 330 69 ilum 447 94 antilium 127 27 femur 480 100 tibia-astragalus 535 111 metatarsal I1 325 68 metatarsal 111 365 76 metatarsal IV 348 73 metatarsal V 118 25 phalanx 11-1 (pes) 85 18 phalanx 11-2 35 7 phalanx 11-3 56+ + 12 phalanx 111-1 78 16 phalanx 111-2 54 11 phalanx 111-3 39 8 phalanx 111-4 52+ + 11 phalanx IV-I 47 10 phalanx IV-2 26 5 phalanx IV-3 19 4 phalanx IV-4 18 4 phalanx IV-5 50+ + 10 digit 111 pes 223 47

+approximate + +measured along dorsal curve

length of vertebral centra (AMNH 5339): cervical 2 46 caudal 1

3 60 2 4 77 3 5 79 4

10 75 dorsal 1 63

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FIG. 2. Struthiomim~s altus. A M N H 5355, occipital aspect of braincase, X*.

preserved occipital region (Fig. 2) and left frontal are present of the skull of AMNH 5355. The sub-arcuate fossa in this individual is relatively much larger, and the medullary cavity is shorter and deeper than in Dromaeosaurus (see Colbert and Russell 1969, Fig. 7b). The frontal is somewhat broader, but otherwise apparently similar to that of Dromiceiomimus (NMC 12228).

A well-preserved muzzle with associated lower jaws (ROM 1790) provides the basis for the reconstruction of the preorbital region of the skull in S. altus (Fig. 3). The palatal region is slightly distorted and difficult to in- terpret. Medially a smooth horizontal sheet of bone, evidently representing the broadened ventral surfaces of the vomers and pterygoids, forms the roof of the oral cavity. If this structure did not contact the anterior part of the maxilla, to which it has been crushed, then the internal nares were possibly situated on either side of the vomeropterygoid bar in the normal theropod fashion. More probably, however, the median sheet-like structure naturally contacts the medially ascending lamina of the edentulous maxilla in this region, displacing the internal nares posteriorly at least as far back as the area below the center of the antorbital fenestrae. There are no internal narial openings present medial to the anterior part of the maxilla in Dromiceiomimus (ROM 840, see also Parks 1928, Plate 4), and the evidence suggests that a secondary palate was present in ornithomimids.

As preserved, the dorsal region of the vertebral column in AMNH 5339 has been shor- tened by the post-mortem rotation of the vertebral centra, which lie at angles to the sagittal plane of the skeleton. This shortening is reflected in Osborn's (1917, p. 744, Plate 26) estimation of the length of the dorsal vertebrae and his reconstruction of the skeleton, and in Sternberg's (1933, p. 79) remark that the pectoral girdle was situated in a position which seemed to abnormally shorten the body in Osborn's reconstruction. The lengths of the appendicular elements of AMNH 5421 and AMNH 5339 are nearly identical, suggesting the animals were probably similar in other bodily measurements. As articulated, the eight posterior dorsal vertebrae of AMNH 5421 measure approximately 525 mm in length. Considering the lengths of the 3 preserved anterior dorsal centra of AMNH 5339, the combined length of the twelve dorsal centra was probably not less than 761 mm in these specimens. This measurement (see Table 3), has been used in the skeletal reconstruction of S. altus presented here (Fig. 1 ). Osborn's ( 1917, Plate 26) reconstruction is confusing in that the vertebra indicated as the thirteenth dorsal would actually be the fourteenth, and it is drawn in a position slightly behind that of the first sacral vertebra in other specimens of this species (AMNH 5421, ROM 1790).

The concave ventral profile of the body in this reconstruction and that of Dromiceiomimus brevitertius (Fig. 4) is duplicated in the arrangement of the gastralia of AMNH 5339 (Osborn 1917, Plate 24) and NMC 8632 (Ornithomimus edmontonicus) .

The presacral vertebral column is longer relative to the elements of the hind limb in Struthiomimus than it is in Ornithomimus and Dromiceiomimus, and the fleshy portion of the

I

FIG. 3. Struthiomimus altus. Reconstruction of skull, lateral aspect, after AMN'H 5339, ROM 1790, X about a.

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RUSSELL: LATE CRETACEOUS OSTRICH DTNOSAWRS

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tail (as indicated by the transverse processes) is also long in this genus. Presumably Struthio- mimus was adapted to a less cursorial mode of existence than were these 2 genera. The forearm and manus are much more powerfully constructed than in Ornithomimus and Dro- miceiomimus, and perhaps better suited for digging. It should be noted that the tarsals in S. altus (AMNH 5339) are similar to those of Archaeornithomimus asiaticus (Gilmore 1933, Fig. 7) , as Lambe (1902, Fig. l l d ) incorrectly restored the broken elements in NMC 930.

Genus Dromiceiomimus (new genus) Diagnosis Length of presacral vertebral column less than combined lengths of femur, tibia-astragalus, and third metatarsal. Posterior width of anteriormost 15 caudal centra less than half of central length, transition point between proximal and distal segments of tail occurs between caudals 12 and 13. Humerus shorter than scapula. Length of antebrachium estimated to be about 70% that of femur. Manus incompletely known, evidently not as powerfully developed as in Struthiomimus; manus unguals probably similar to those of Ornithomimus edmontonicus (Parks 1928, p. 24). Antilium, tibia, metatarsus, and digit 3 of pes longer relative to femur than in Ornitho- mimus and Struthiomimus.

Discussion A long limbed ostrich dinosaur (Fig. 4) seems to be at least as common in the lower Edmonton Formation as Struthio- mimus altus is in the Oldman Formation, both forms being the most abundant ornithomimid in the area of outcrop of their respective geo- logic units along the Red Deer River. Morpho- logically the Edmonton form is as distinct from Ornithomimus and Struthiomimus as these genera are from each other. It is therefore given the binomial name of Dromiceiomimus brevitertius (Parks 1926) and regarded as the type species of the genus. A single specimen (ROM 840) may document the presence of Dromiceiomimus in the Oldman Formation.

Dromiceiomimus brevitertius (Parks 1926) Struthiomimus brevitertius Parks 1926, p. 65;

emended Sternberg 1933, p. 79. Struthiomimus ingens Parks 1933, p. 13.

Distribution Members A and B, Edmonton Formation, Red Deer River, Alberta.

Type ROM 797, sacrum and adjacent caudal vertebrae, several distal caudal vertebrae, pelvis, both hind limbs (?section 3, township 30, range 21, west of Fourth meridian, approximately 38 m above the east bank of the Red Deer River, member A of the Edmonton For- mation).

Referred specimens AMNH 5201, both humeri, both pubes and ischia, left femur, both tibiae-fibulae, metatarsal fragments, phalangial elements of left pes (?section 19, township 34, range 21, west of Fourth meridian, approximately 9 m above west bank of Red Deer River, member B of the Edmonton Formation).

NMC 12068, sacrum and adjacent dorsal vertebrae, tail, left ilium, both pubes and ischia, both hind limbs (northeast quarter section 28, township 34, range 21, west of Fourth meridian, 55 m above east bank of Red Deer River, member B of Edmonton Formation).

NMC 12069, proximal and distal ends of tail, distal ends of both pubes and ischia, left femur, both tibiae-fibulae and feet (same locality as NMC 12068).

NMC 12070, distal ends of both tibiae, both metatarsi, pedal phalanges (same locality as NMC 12068).

NMC 12228, posterodorsal region of skull, left temporal region, anterior half of left mandible, posterior half of right mandible, incomplete presacral vertebral column, nearly complete tail, left ilium, both pubes and ischia, left femur and tibia-fibula, left metatarsus, two pedal phalanges (section 28, township 3 1, range 21, west of Fourth meridian, approximately 44 m above west bank of Red Deer River, member B of Edmonton Formation).

ROM 852 (type of Dromiceiomimus ingens), sacrum and adjacent dorsal vertebrae, pelvis, complete left hind limb, right femur and tibia, proximal end of right fibula (?section 10, township 30, range 21, west of Fourth meridian, approximately 61 m above the east bank of the Red Deer River, member B of the Edmonton Formation). Discussion In his original description of the

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FIG. 5 . Dromiceiomimus brevitertius. A. Recon- struction of skull, dorsal aspect, after NMC 12228, ROM 840, X+. B. Same structure in lateral aspect.

type specimen, Parks emphasized the fact that the proximal end of the third metatarsal is unossified. He also noted (Parks 1926, p. 68) ". . . the proximal view of the metatarsus . . . disclosed no recess for a missing bone, as Meta- tarsals I1 and IV are quite closely apposed with no re-entrant angle between them" so that the condition cannot be ascribed to the juve- nility of the specimen. The proportions of the elements of the pelvis and hind limbs correspond very closely to those in other specimens assigned to this species. An incorrect plaster restoration of the posterior zygapophyseal region was incorporated into the illustration of a distal caudal vertebra (Parks 1926, Fig. I ) , and there are no additional skeletal peculiarities. The unusual nature of the third metatarsal may be best considered as an individual abnormality. The differences between the relative proportions of the pelvic girdle and hind limb in the type of D. brevitertius and that of D. ingens (ROM 852) are due to allometric changes associated with the greater maturity of the latter specimen.

The material presently referred to the species under discussion does not include specimens as complete as those which have been referred to Ornithomimus edmontonicus and Struthiomi- mus altus. The best specimen available of D. brevitertius is NMC 12228, in which the muzzle, braincase, many presacral vertebrae, sacrum, pectoral girdle, and forelimbs are missing. Some of its cranial elements are, however, unusually well preserved.

Skull The shape of the bones of the temporal and orbital regions is shown in Fig. 5. The reduction of the temporal fossa and enormous size of the orbit are striking. The supratemporal fenestra appears to be bordered laterally and medially by alae of the squamosal, but the sutures are difficult to trace in this region. The orbital rim measures approximately 72 mm in diameter, as compared with a measurement of 55 mm in an ostrich of similar body size (NMC 5638, palaeontology collection). In contrast to conditions in the ostrich, the orbital margins lie closer to and more nearly parallel the sagittal plane of the skull. As a result the orbital fossa is shallower and the eyeball was flattened. The area of the retina was evidently larger than in any living terrestrial vertebrate, and the visual sense must have been exceedingly acute, correlating with the animal's dependence on vision to detect danger and its cursorial habits (see Walls 1942, pp. 171-174, 642).

The skull of NMC 12228 was surely kinetic, although its incompleteness precludes an ade- quate understanding of the kinetic mechanism. The distal end of the quadrate must have been capable of limited anteroposterior movement, pivoting about a cotylus on the undersurface of the squamosal. The anterior ends of the frontals are very thin in this specimen, as is the bridge of the nasals situated above the antorbital fenestrae in other ornithomimid specimens (ROM 840, 851, 1790). The beak was probably rotated in a vertical arc about this flexible bridge by the force imparted to the quadratojugals and jugals from the motion of the distal end of the quadrates, paralleling the situation in birds (Bock 1964). However, in marked contrast to avian conditions, the braincase is not closely associated with the parietal region of the skull roof. Movement about a meso- kinetic axis was suppressed by the firm sutural union of the frontals and parietals. The primitive (metakinetic) transverse axis of rotation between the suspensorium and paroccipital processes may have been replaced by a loose articulation which facilitated movement between the skull roof and braincase about an axis located elsewhere in the skull. The postero- ventral surface of the parietal (NMC 12228, ROM 840) and dorsal edge of the supra- occipital (ROM 840) are smooth, and a metakinetic joint was therefore absent. However, a

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FIG. 6. Dromiceiomimus brevitertius. A. Endo- cranial mold of NMC 12228, dorsal aspect, X+. B. Same structure in lateral aspect.

transverse axis of rotation probably existed between the opposite contacts of the lateral process of the laterosphenoids with the post- orbital and adjacent areas of the frontal and parietal. Displacement of the braincase relative to the skull roof along this axis, and ventrally between the basisphenoid and pterygoids, may have assisted kinetic movement in a manner analogous to that described by Russell ( 1964) in mosasaurs.

The general shape of the structure of the forebrain is clearly visible in NMC 12228, and a reconstruction of the endocranial mold of this region is presented here (Fig. 6). The olfactory bulbs are short and thin. The cerebral hemispheres are only slightly wider than in Stenonychosaurus (see Russell 1969, Fig. 3c), but are much deeper and more arcuate in lateral aspect. Volumetrically they are about twice as large as the same structures in Steno- nychosaurus. There is a peculiar bulb on the anterolateral surface of the cerebral hemispheres which is not present in Stenonycho- saurus or Dromaeosaurus (NMC 12349). The parietal foramen is absent in all known higher archosaurs, but it is interesting to note a small excavation in the ventral surface of the parietal, which evidently contained a parietal organ. Farther posteriorly the ventral surface of the parietal is smooth, and shows no trace of endocranial structures. The firm attachment of the rhombencephalon to the braincase walls through the cranial nerves and flocculus (to the subarcuate fossa) necessitated that the dorsal regions of the brain stem be but loosely attached to the cranial roof in order for kinetic

movement to take place. The general relation of brain size to body weight in NMC 12228 appears to be similar to that of an ostrich of comparable size (NMC 5638, palaeontology collection).

Skeletal reconstruction As noted above, the material referred to Dromiceiomimus brevitertius does not include such complete and well preserved skeletons as are available of Ornitho- mirnus and Struthiomimus. Nevertheless, a reconstruction of the skeleton of this form seems advisable to serve as a visual aid in defining its identity. The reconstruction is largely based on NMC 12228, the most nearly complete available specimen. Skeletal parts of other specimens belonging to Dromiceiomimus have also been incorporated, drawn to correspond to the dimensions of NMC 12228, in order to complete the reconstruction.

The lengths of the preserved presacral centra of NMC 12228, are given in Table 4, together with the estimated lengths of the missing last two cervical centra. The cervical series must have measured approximately 635 mm in length. Only 4 dorsal vertebrae are preserved, but the ribs on the left side of the body, left ilium and base of tail all seem to be in their natural positions. The anteroventral point of the iliac blade marks the approximate position of the posterior face of the twelfth dorsal centrum in this species (NMC 12068, ROM 852). The distance between this point and the posterior face of the seventh dorsal centrum, paralleling the axial curve of the body, is 307 mm. The articulated length of dorsals 7 to 4 is 240 mm, and that of the first three dorsal centra is estimated to have been 165 mm, yielding an approximate length of the dorsal segment of the vertebral column of 712 mm.

The sacrum and first caudal vertebra are not preserved in NMC 12228. The distance between the anteroventral point of the ilium and the anterior face of the second caudal centrum is 440 mm. If the length of the first caudal centrum and its associated intervertebral discs is considered to have been about 67 mm, then the combined length of 6 sacral centra would amount to 373 mm.

A nearly complete caudal series was preserved with NMC 12069 (see Table 4), but a small wash subsequently carried away 635 mm of the middle region of the tail (C. M. Stern-

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TABLE 4. Dromiceiomimus breuitertius, length of skeletal elements

NMC 12228

(% of femur (mm) length) ROM 852 AMNH 5201

-

skull 240 + 5 1 +

cervical vertebrae 635 + 136 - cervicals 4-10 520 + 111 - 12 dorsal vertebrae 712+ 152 - dorsals 1-7 395 + 83 - sacrum 373 + 80 - 12 basal caudal vertebrae 723 + 154 - scapula - - - humerus - - - ulna - - - digit 11, manus - - - ilium 478 1 02 435 antilium 164 35 152 femur 468 100 432 tibia-astragalus 578 123 537 metatarsus 397+ 85 372 digit 111, pes 255 + 54 240 -t Length of presacral centra (NMC 12228):

altas-axis 50 cervical 3 65

4 76 5 75 6 75 7 78 8 80 9 75 +

10 61 + dorsal 4 58

5 57 6 58 7 59

Length of caudal centra: NMC 12228 NMC 12069 1 - - 2 55 - 3 54 - 4 - - 5 57 43 6 55 43 7 57 43 8 57 43 9 57 -

10 59 +

11 63 - 12 58 - 13 60 - 14 57 - 15 59 - 16 58 - 17 59 - 18 63 - 19 64 - 20 62 - 21 60 - 22 57 - 23 + 43 24 - 41 25 - 40 26 - 37 27 - - 28 - 31 29 - 26 30 - 24 31 - 23 32 - 18

+Estimated.

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3 92 CANADIAN JOURNAL OF EA ,RTH SCIENCES. VOL. 9, 1972

berg 1926, field notes). The chevrons of the remaining proximal segment indicate, by comparison with those of NMC 12228, that caudals 5 through 8 are present and average 43 mm in length. In NMC 12228 the lengths of the caudal centra increase slightly from caudal 9 posteriorly, and do not decrease to equal caudal centrum 9 in length until the 22nd caudal is reached, the last one preserved in this specimen. The fact that the centrum of the anteriormost preserved vertebra of the distal segment is equal to that of the eighth caudal in length suggests that at least 13 caudal vertebrae were lost in NMC 12069. If an additional vertebra is added to this figure, the average length of vertebral centra in the missing segment would amount to approximately 45.3 mm, a reasonable figure. The distal segment of the tail, containing 10 vertebrae, measures 330 mm in length, and it is unlikely that more than one or two terminal elements are missing. By comparison with proximal caudals in NMC 12228 it is estimated that the basal four caudals of NMC 12069 would have had a combined length of about 17'0 mm. The tail, therefore, of NMC 12069 probably contained 32-33 vertebrae and had an overall length of approximately 1308 mm.

A total of 32 vertebrae are incorporated within the tail of the reconstruction of D. brevitertius. The majority of them, and associated chevrons, were drawn from NMC 12228. The 10 distal segments were drawn from NMC 12069, with their proportions suitably increased to correspond to those of the larger specimen. The total length of the tail in NMC 12228 is estimated to have been 1690 mm.

The humerus is known in only one specimen of D. brevitertius (AMNH 5201, see Osborn 1917, Fig. 7 ) , where its length amounts to 75% of that of the femur. If the relative lengths of these bones were similar, the humerus in NMC 12228 would have been 350 mm long. The shoulder girdle and antebrachium in the reconstruction are restored after these structures in ROM 840 (D. samueli, Oldman Formation), assuming their lengths relative to that of the humerus were similar in the Edmon- ton form. The lengths of the metacarpals and form of the manus are conjectural. They may have been elongate also, corresponding with the length of the forearm and bringing the

manal claws closer to the ground. The proportions of the distal end of the pubis and most of the pedal phalanges are restored after these elements in ROM 852, assuming their lengths were similar relative to that of the femur in NMC 12228.

Dromiceiomimus samueli (Parks 1928) Struthiomimus samueli Parks 1928, p. 6.

Distribution Oldman Formation, Red Deer River, Alberta.

Type ROM 840, skull and lower jaws, cervical and anterior dorsal vertebrae, both scapulae- caracoida and humeri, right radius-ulna, proximal end right metacarpus, two ungual phalanges (quarry 12 of Sternberg 1950, Oldman For- mation, Dinosaur Provincial Park).

Discussion The type specimen of this species was described in detail by Parks ( 1928), who published a reconstruction of the skull which was quite good in view of the crushed condition of the original structure. However, the supratemporal fenestra is not bridged by a transverse bar of bone, and the quadratojugal does not contact the posterior rim of the post- orbital bar, but lies medial to it in this region. The peculiarities of the pectoral girdle and forearm preclude the assignment of the species to either Ornithomimus or Struthiomimus. The detailed resemblance of the preserved cranial bones of NMC 12228 to corresponding elements in ROM 840 provides the basis for referring the latter specimen to Dromiceio- mimus. Unfortunately the hind limbs are unknown in D. samueli, but the length of the antebrachium suggests they were long in this form also.

D. samueli may be distinguished from D. brevitertius in that the humerus is approximately five times longer than an anterior dorsal centrum of average proportions, while in the latter species it may be nearly six times longer. The cranial bones are more heavily constructed in ROM 840 than in NMC 12228, but this difference may not have taxonomic significance.

Lancian Ornithomimids in Canada

Isolated ornithomimid material, usually con- sisting of pedal phalanges and distal caudal vertebrae, has been recovered from deposits of

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Lancian or latest Cretaceous age in southern (?section 34, township 30, range 21, west Canada. Perhaps worthy of note are an ungual of Fourth meridian, approximately 23 m from the Frenchman Formation of Saskatche- above east bank of Red Deer River, member wan (NMC 9819) which resembles that of A of Edmonton Formation). the first digit in the hand of Struthiomimus, UA field number 21, 1921, skeletal material, and another manus ungual from the upper Oldman Formation, Red Deer River). Edmonton Formation in south central Alberta (NMC 9560) which is straighter and more elongate, as in Ornithomimus.

Undetermined Material AMNH 5262, distal caudal vertebrae, two pedal

phalanges (?section 8, township 32, range 2 1, west of Fourth meridian, approximately 18 m above east bank of Red Deer River, member B of Edmonton Formation).

AMNH 5264, pedal elements (?section 8, township 32, range 21, west of the Fourth meridian, approximately 18 m above east bank of Red Deer River, member B of Edmonton Formation).

AMNH 5380, posterior region of skeleton, unprepared (basin of Little Sandhill Creek, Oldman Formation, Dinosaur Provincial Park).

AMNH 6175, ungual phalanges of pes (Old- man Formation, Red Deer River).

BMNH R4861, pedal elements (Oldman For- mation, Red Deer River).

NMC 12224, posterior part of sacrum and right ilium, acetabular area of right pubis, both ischia (2.4 km south of Steveville ferry crossing, Oldman Formation, Dinosaur Pro- vincial Park).

NMC 12227, fragments of both tibiae-fibulae, distal ends of left metatarsals, right fourth metatarsal, 3 pedal phalanges (section 33, township 30, range 21, west of Fourth meridian, approximately 34 m above west bank of Red Deer River, member A of Edmonton Formation).

NMC field number 17, 191 3, pedal elements (Oldman Formation, Dinosaur Provincial Park).

NMC field number 3, 1916, pedal elements now in Regina Museum, Saskatchewan (section 18, township 32, range 21, west of Fourth meridian, approximately 1 1 m above west bank of Red Deer River, member B of Edmonton Formation).

ROM field number 1, 1923, unprepared pelvis I

Myology of the Ornithomimid Thigh It is quite apparent from even a casual ap-

praisal of the ornithomimid skeleton that the animals were well adapted for rapid progres- sion an the land. The muscles have left relatively well-marked scars on the pelvis and femur, and, with the aid of Romer's publica- tions on the musculature of the reptile thigh, it has not been difficult to reconstruct the myology of this region. Morphologically speak- ing, the muscular system of reptiles would seem to be about as subject to variation as is the skeletal system. One would expect that, although muscles (and bones) may vary in shape in different taxa, their topographic relationships with other muscles (and other bones) would remain basically conservative. The following reconstruction (Figs. 7, 8) is proposed in the hope that it may correspond fairly well, therefore, with the actual arrangement of the thigh mmules in the long-extinct ornithomimids.

The iliofemoralis originated from a very large area of the broad lateral surface of the ilium, and most likely inserted on the proximolateral trochanters of the femur through a pre- acetabular and postacetabular head. Romer (1932b, Fig. 5) shows the iliofemoral is in Tyrannosaurus inserting on the lateral surface of the femoral shaft, as in crocodiles. However, the dorsal displacement of the area of insertion of this muscle, culminating in the developmat of proximolateral trochanters, is clearly evident in the evolution of b i p d d archosaurs (cf. Ornithosuchus, Walker 1964, Fig. 12; Megalo- suurus, Owen 1857, PIate 7; Allosaurus, Gil- more 1920, Plate 14), and may be interpreted as a consequence of the vertical posture of the femur, The anterior and posterior heads of the iliofemoralis were separated by a rounded vertical ridge on the ilium in tyrannosaurids, while in ornithomimids the crests markiug the adjacent boundaries of these heads are separated by a shallow sulcus. The iliotibialis was a powerful sheet of muscle fibers originating from

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Flu. 7. lateral view of pelvic region of Dromiccfomimus (Ieft side) showing appendiculm muscles restored. Abbreviations : CFB, caudifemoralis brevis; CFL, caudif emoralis longus; ITT, flexor tibjalis; m, femorotibiah; G, gaslrmnemius; IC, ischiocaudalis; IF, ifiofemorali~ (a--anterior head, ppmterior head); IFB, iliofibularis; I=, iliocaudalis; IST, ischiotrochan- tericus; IT, iliotibialis; PIFE, puboischiofemoralis externus (i-ischiadic head, p-pubic head); PIFI, pnboischiofemoraLis internus (i-ischiadic head, p p u b L head); QL, quadratus lumborum.

the ilium dorsal to the iliofemoralis, and insert- suggested by a scar on the fibula, may not have ing with the femorotibialis on a strongly de- been quite as strong as in tyrannosaurids. The veloped cnemial process from the anteroprox- area of origin of the ambiens is neither exten- imal region of the tibia. The iliofibularis, as sive nor marked by scars, and the muscle could

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FIG. 8. As in Fig. 7, with the caudifemoralis brevis, caudifemoralis longus, flexor tibialis. iliofibularis, and iliotibialis cut away.

not have been as relatively powerful as it was pubis and ischium (Romer 1942). Because in tyrannosaurids or Saurornithoides (Russell both of these once continuous sheets were

1 1969). fragmented into anterior and posterior heads 1 The puboischiofemoralis muscles are derived by the development of a large fenestra within

embryologically from adjacent sheets of dorsal the puboischiadic symphasis of theropods and ventral appendicular muscle tissue, sepa- (Romer 1923b), it is convenient to consider rated from each other by the blades of the them together in spite of their discrete onto-

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genetic derivations. The fragmentation of these muscles must have been further accentuated in ornithomimids by the need for long muscle fibers to accommodate a long anteroposterior swing of the femur, and which produced a distal migration of their areas or origin and a corresponding lengthening of the pubis and ischium. Shorter muscle fibers arising from the region between the distal end of the pubis and ischium and inserting on the limb (medial parts of the puboischiofemoralis muscles and especially the puboischiotibialis) were probably lost entirely, in order to facilitate an increased length of stride.

The puboischiofemoralis externus probably arose from the distolateral surfaces of the pubis and ischium and inserted on a pronounced scar on the medial surface of the proximal half of the femur (see Fig. 8) . This scar is more pronounced and more anteriorly situated than the homologous structure in tyrannosaurids (cf. Osborn 1917, Figs. 8 and 21a). A pubic head of the puboischiofernoralis internus (representing the first division of the puboischiofemoralis externus of Romer 1923a, p. 542, in crocodiles, and third division of the puboischiofemoralis internus of Romer 1942, in lizards) probably also inserted on this scar. Romer (1923a, p. 535; 1923b, p. 611) noted that in crocodiles the rectus muscles insert primarily on the last gastral rib, which is in turn attached ligament- ously to the ventral tip and a small area of the lateral shaft of the pubes. A similar arrangement probably existed in ornithomimids, for here the gastralia also become more powerfully developed posteriorly (Sternberg 1933, Fig. 1 ) . There is no reason to suspect that the attachment of the last gastral rib to the pubis in ornithomimids would have interfered with the development of a pubic head of the puboischiofemoralis internus. The ischiadic head of this muscle probably passed below the anterior edge of the pubic peduncle of the ilium to insert with the quadratus lumborum on the proximal end of the femur, medial to the lateral trochanter. The posterior limit of the area of origin of the ischiadic head may have been con- fined to the sacral area, as in crocodiles (Romer 1923a, p. 547, Plate 24). More probably, however, it extended back along the ischiadic symphasis as in lizards (Romer 1942, Fig. 14) to allow a greater anteroposterior swing of the femur.

The anterior blade of the ilium is laterally deflected and smoothly incised ventrally in ornithomimids, to accommodate the two large muscle masses passing back from the transverse processes and neural arches of the preacetabu- lar vertebrae. The more superficial of these (quadratus lumborum, or second division of the puboischiofemoralis internus of Romer 1923h) probably inserted on the medial surface of the proximolateral trochanters, while the medial muscle mass (fitst division of the puboischiofemoralis internus of Romer 19233) probably joined the ventral components of the puboischiofemoralis in inserting on the scar on the medial surface of the femoral shaft. In view of the straight anterior margin of the pubis, the absence of muscular scars on its anterolateral surface, and the complex development of other powerful femoral protractors in this region, it is difficult to imagine that an ambiens muscle was present in ornithomimids.

In conformity with the postulated weakness of the iliofibularis and the frail construction of the posterior blade of the ilium, the flexor tibialis muscles were probably not strong. The most important sources of energy for femoral adduction must have been supplied by the caudifemoralis muscles. The caudifemoralis brevis, as indicated by the lateral displacement of the posterior blade of the ilium, possessed a diameter equal to the depth of this part of the iliac blade. The caudifemoralis longus, with a similar cross-sectional area, as evidenced by the length of the transverse processes at the base of the tail, was probably tendonously linked to the gastrocnemius, as in modern lizards and crocodiles (Romer 1942, p. 283). In both ornithomimids and tyrannosaurids the heavily scarred area marking the attachment of this muscular complex is situated on the posterior surface of the femur well below the middle of the shaft (Osborn 1917, Fig. 8,21a3).

The ischiocaudalis is here considered to have taken as its major point of insertion the deep, sharply defined scar on the proximoposterior margin of the ischium where Romer ( 1923b) placed the origin of a division of the flexor tibialis internus. The surface texture of the scar in ornithomimids and tyrannosaurids suggests that the tendonous fibers came from behind, not below. A division of the flexor tibialis internus may well have originated instead on the crest of bone forming the anterior boundary of

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TABLE 5. Bodily proportions expressed as percentage of length of tibia-astragalus in ostrich and ornithomimids

Struthio Ornithomimus Struthiomimus Dromiceiomimus (NMC 5638) (ROM 851) (AMNH 5339) (restoration)

skull 38 neck 167 trunk* 105 tail? 98 ilium 108 femur 58 tibia-astragalus

(length in mm) 498 metatarsus 89 third pedal digit 42 hind limb 289

*Measured from base of neck to anterior border of acetabulum. ?Measured from posterior border of acetabulum to distal end of tail.

the scarred area. It is also probable that the ischiocaudalis was linked to the distal end of the ischium through cloaca1 structures, as in crocodiles (Romer 1923a, p. 536).

Although ornithomimids are not usually considered to have been saltorial animals, it may be instructive to contrast the structure of their hind limbs with those of a kangaroo (NMC mammalogy collection no. 2865 1 ) . The heavy scars on the greater trochanter, posterior surface of the femur, calcaneal tuber and flexor tuberosities of the phalanges all suggest that the muscle insertions are much more tendonous in kangaroos than they were in ornithomimids. The tibia is long in the kangaroo, perhaps to increase the elastic amplitude of muscles and ligaments inserting on the calcaneal tuber, but the metatarsus is quite short and probably transmits a large percentage of the adductor pulse applied to the calcaneal tuber to the substrate. In ornithomimids, however, there is no posterior tuber developed from the tarsus and the metatarsus is relatively longer than in kangaroos. It is very improbable that the ornithomimid hind limb contained the resilience of that of the kangaroo. However, the cnemial crest of the tibia is much more highly developed in ornithomimids, indicating the recovery stroke of the limb was stronger and more complete. It may be concluded that the ornithomimid hind limb was much better suited for running than for bounding.

Cursorid Ability of Struthw and Dromicewmimus Compared

As a consequence of their cursorial adaptations ostriches and ornithomimids are similarly

proportioned (see Table 5), but there are fundamental differences in the structure of the pelvic area which reflect their respective avian and theropodous ancestries. In ostriches, where the tail is relatively small, the major femoral retractors originate on an elongate, static ilium. More anteriorly, the femoral protractors also originate on the ilium, as the anteroventral region of the pelvis is rudimentary in birds. In ornithomimids, however, the major femoral retractors originated from the hypaxial region of the tail, and the epaxial musculature in concert with the caudal centra alternately re- sisted the pull of contracting retractors of each leg, stabilizing the tail in the same way that rigging stabilizes the bowsprit of a sailing ves- sel. A specimen of Struthio (NMC 3638) and Dromiceiomimus (NMC 12228) were of approximately the same body weight, as evidenced by the similar diameters of the femur and estimates of the bodily volume in the two animals. It may be useful to compare the locomotor apparatus of these specimens.

The relative lengths of the ostrich and Dro- miceiomimus femur are represented by heavy straight lines in Figs. 9 and 10, and the hypo- thetical directions of application of muscle force are indicated by arrows, assuming the femur to be oriented in a vertical position. The orientation of the pelvic muscles of the ostrich is after Gadow (1880) and Gregory and Camp (19 18), and the terminology is that used by the latter authors.

It was determined graphically that the moment arms (leverage) of the femoral retractors of the ornithomimid exceed those .of the ostrich by approximately the same relative amount as

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CANADIAN JOURNAL OF EARTH SCIENCES. VOL. 9, 1972

\-

FIG. 9. Major directions of muscle action (mows) and correspondmg lever arms (dotted lines), with the femur held perpendicular to the long axis of the pelvis in Strrcthio. The pelvis is represented by a horizontal line extending between two smaU vertical lines, and the femur by a heavy vertical bar. Abbreviations: cif, caudi-iliofemoralis; cifl, caudi-ilioflexorius; if. ilio- fernoralis; ifb, iliofibularis; ifl, ischioflexorius; pifp, puboischiofemoralis posterior; sa, sartorius.

the total length of the hid limb in the ornithomimid exceeds that of the ostrich (see Table 6), Since the femoral protractors accelerate only the leg instead of the entire mass of the animal, they need not be as powerful as the retractors, but here the moment arms of the muscles exceed those of comparable muscles in the ostrich by an even greater degree. An inspection of the pelvic areas of both specimens suggests intuitively that the ornithornimid was at least as muscular as the ostrich in this region. If the force generated by a given volume of muscle were similar in the two animals, the simplified model outlined here suggests that the stride of the ornithomimid was longer, the work

capacity of the legs was greater, and that the amount of time consumed by each running step was smaller (see the power of the femora1 protractors), An ostrich is capable of attaining an average speed of approximately 69 km/h (43 mph) for 1.6 km ( 1 mile, personal com- mun: C. S. Churcher 1969) or 80 km/h (50 mph) for 0.8 krn (3 mi, Howell 1944, p. 25).

Ornithomimids were probably much less maneuverable than ostriches when running. In ostriches the iliotrochantericus, iliofemoralis externus and obturator externus insert on the proximolateral trochanter of the femur at angles of approximately 120" to each other. This

TABU 6. IRngth of lever anns of pelvic muscles*

Dromiceinmimus Struthio Dromiceiomimus/Siruthio

Protractors: PIFE, PIPI 160 sa 114 1wk IT 58 if 38 153%

Retractors : CFL 250 cifl, ifl214 117% FLT, IFB 154 ifib, pifp 112 137%

CFB 90 cif 84 107%

Length of leg: 1698 1440 118%

'Compare with Fiw. 9 and 10, for abbreviations soc Figs. 7 and 9.

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FIG. 10. Major directions of muscle action and lever arms in Dromiceiomimus. For expla- nation and abbreviations see Figs. 7 and 9.

tripodal arrangement pivots about the much more medially situated head of the femur, and probably facilitates rotation of the femoral shaft about its long axis as well as movement in a transverse plane. The more distal insertion of major femoral pro- and retractors, coupled with their orientation which tended to parallel the longitudinal axis of the body, must have restricted movement of the ornithomimid hind limb to an essentially vertical anteroposterior plane.

The Biology of Ornithomimids The suggestions offered below on the pos-

sible habits of ornithomimids are only specula- tions which seem to be consistent with what is known of their morphology and environment. Similar remarks made by Gregory (in Osborn

1917, pp. 758-760) are worthy of special attention. The animals had an exceptionally keen sense of vision and an intelligence which was probably comparable to that of living ratites. Their coloration may have been affected by the possible presence of color vision in their predators, in contrast to conditions in modern mammalian carnivores (Walls 1942, p. 508).

In view of the strongly carnivorous adaptations of other theropods, it seems unlikely that ornithomimids fed on vegetable matter. Gastric stones have never been reported in association with articulated skeletal material. As noted by Osborn (1917, p. 757) the muzzle may have had a horny covering. The development of a bony vault over the anterior part of the oral cavity (secondary palate) and a transverse axis of flexure in the skull roof anterior to the orbits, together with the general shape of the

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TABLE 7. Growth changes in length of elements of pelvic girdle and hind limb, expressed as percentage of femur length

fern ilium pubis ischium tibia-astrag. metatarsus (mm) (7%) (7%) (%I (%I (%I

Struthiomimus altus AMNH 5385 367 - - - ROM 1790 397 94 - 67 AMNH 5421 475 101 - - AMNH 5339 480 94 95 67 AMNH 5257 513 - 100 - Dromieciomimus brevitertius NMC 12069 361 - AMNH 5201 378 +

ROM 797 383 - ROM 852 432 101 NMC 12068 440 103 NMC 12228 468 102

muzzle, recall the morphology of the bill in modem insectivorous birds. The jaw adductor muscles were very weakly developed in ornithomimids, suggesting the animals fed on soft- bodied animals or eggs. The hands were probably used in uncovering food objects through the removal of light material resting on the surface of the ground (Ornithomimus, Dro- miceiomimus) , or by actual digging (Struthio- mimus, see Gregory in Osborn 1917). They lacked the suppleness to transport food objects to the head (Ostrom 1969, pp. 108-109).

Although their coloration may have served as an excellent camouflage, a static ornithomimid must have been virtually defenseless. They were probably attacked by dromaeo- saurids, and particularly by juvenile tyrannosaurids, which are much more lightly constructed and possess relatively longer hind limbs than the adults (D. A. Russell 1970). The surprising strength and efficiency of the hind limbs in ornithomimids were probably crucially important in accelerating the animal out of a dangerous situation. Evidently the natural enemies of orni@omimids were not very maneuverable, which may have been a consequence of their relatively more massive bodies.

The pelvic canal is very wide in ornithomimids, and especially so in Dromiceiomimus. In NMC 12228 the maximum internal width of the pelvic canal is 125 mm, while the same measurement amounts to only 160 mm in an adult tyrannosaurid at least 8 m (26 ft) long in standing position (NMC 8506). Whether ornithomimids laid eggs or were ovovivaporous,

the relatively well developed young presumably had stronger legs and an enhanced probability of survival. In consideration of the large size of the pelvic canal and small size of the body in omithomimids is possible that the number of eggs or young produced at a given time was smaller than in other theropods. Allometric changes in the proportions of the pelvis and hind limbs are negligible in Struthiomimus altus (see Table 7). In Dromiceiomimus brevitertius, however, which seems to be the more cursorial of the two species, the lengths of the pubis and ischium decrease, and the length of the metatarsus increases, relative to the length of the femur during the growth of the animal. The concomitant increase in the volume of pelvic muscles and length of stride must have com- pensated for the detrimental effect of the increased bodily mass of more mature individuals while running. One adult (NMC 12068) and two approximately half-grown specimens (NMC 12069, NMC 12070) of this species were collected at one site in the Edmonton Formation. The occurrence may be indicative of herding habits to increase the probability of detecting danger, or of parental care.

Summary and Conclusion

Omithomimoid dinosaurs were probably derived from a group of lightly-built, more conservative theropods during middle Jurassic time. By late Jurassic (Elaphrosaurus) and early Cretaceous (Archaeornithomimus) time the animals were apparently already relying on their fleetness for defense, rather than the pug- nacious use of teeth and claws in a manner

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1 RUSSELL: LATE CRETACEC

more typical of tetrapod carnivores. The skeletons of late Cretaceous forms, with their lightly- built bodies and powerful hind limbs, represent a degree of adaptation to a cursorial mode of existence which has not often been equalled in the history of life on Earth. The three known generic lineages, (Ornithomimus, Struthio- mimus, and Dromiceiomimus) in the late Cre- taceous of western Canada show little evidence of change between the time of deposition of the Oldman Formation and that of the lower Ed- monton Formation. In view of the apparent equivalence of the former unit to marine strata of the Baculites gregoriensis zone, and of the latter unit to those of the upper part of the broadly defined B. compressus zone, both of which occur within the Upper Campanian (Jeletzky 1968, 1971), this fact is not too surprising. At least two undetermined genera of ornithomimids are present in Lance-equivalent (Upper Maestrichtian) strata in western Canada.

Selective pressures originating from comparable modes of life produced grossly similar body forms in the ornithomimid genera of western Canada and large modem ground birds. Both groups possess.(ed) large eyes, a kinetic beak, secondary palate and similar level of intelligence. Ornithomirnids evidently fed on insects, other small animaIs and eggs. At least one genus (Dromiceiomimus) was probably capable of running faster than the ostrich, although it could not dodge as easily. The leg muscles tended to arise more from the axial region of the body than the pelvis, the reverse of conditions in ratites. The arms were long and equipped with claws reminiscent of those of anteaters. Rather tenuous evidence suggests that the young were quite well-developed at birth and may have received some parental care. A combination of adaptations seen in ratite birds and anteaters, superimposed upon the skeletal framework of a theropod must have made the ostrich dinosaurs one of the most peculiar and interesting groups of terrestrial Mesozoic vertebrates.

I Acknowledgments

I I am very grateful to Dr. A. Gordon Edmund, of the Royal Ontario Museum, who in spite of a heavy commitment to a display

)US OSTRICH DINOSAURS 401

program found time to make available the excellent collection of ornithomimids under his care and provide casts and photographs of some of the more important material. Dr. Edwin H. Colbert, Curator Emeritus of the Fossil Rep- tiles and Amphibians of the American Museum of Natural History, allowed me to study the ostrich dinosaurs in the collections of his insti- tution, and had the glass panel removed in front of the beautifully preserved skeleton of Struthiomimus described by Osborn so that it could be re-examined. Dr. John H. Ostrom, of the Peabody Museum of Natural History, Yale University, generously forwarded casts of the type material of Ornithomimus velox, and Dr. Peter M. Galton, of the University of Bridge- port, critically reviewed the section on the myology of the ornithomimid thigh. I have benefited from discussions on Asian ornithomimids with Drs. Halzka Osmolska and Ewa Roniewicz, of the Polish Academy of Science, and with Dr. A. K. Rozhdestvensky, of the Soviet Academy of Science, all of whom generously allowed me to examine ornithomimid materials in their institutions. Special mention is due to Mr. H. L. Shearman, of the National Museum of Natural Sciences, for his skillful preparation of the delicately preserved cranial elements of a Dromiceiomimus specimen in the collections of this museum.

BOCK, W. J. 1964. Kinetics of the avian skull. J. Morphol., 114, pp. 1 a 2 .

COLBERT, E. H. and RUSSELL, D. A. 1969. The small Cretaceous dinosaur Dromaeosaurus. Am. Mus. Nat. Hist., Novitates 2380.

DODSON, P. 1971. Sedimentology and taphonomy of the Oldman Formation (Campanian), Dinosaur Provincial Park, Alberta ('Canada). Palaeogeogr., Palaeoclimatol., Palaeoecol., 10, pp. 21-74.

DOLLO, L. 1883. Notes sur les Dinosauriens ren- contrCs dans la cr6tacC sup6rieur de la Belgique. Mus. Roy. Hist. Nat. Belgique, Bull. 2, pp. 212- 214.

GADOW, H. 1880. Zur vergleichenden Anatomie der Muskulatur des Beckens und der hinteren Glied- masse der Ratiten. Gustav Fischer, Jena, pp. 1-56.

GILMORE, C . W. 1920. Osteology of the carnivorous dinosauria in the United States National Museum. U.S. Natl. Mus., Bull. 110.

1924. Contributions to vertebrate palaeontology. Geol. Surv. Can., Bull. 38.

1933. On the dinosaurian fauna of the Iren Dabasu Formation. Am. Mus. Nat. Hist., Bull. 67, pp. 23-78.

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ostrich dinosaurs from the late cretaceous of western canada

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