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Nowitate MUSEUM ovitates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3420, 19 pp., 12 figures, 1 table October 29, 2003 An Early Ostrich Dinosaur and Implications for Ornithomimosaur Phylogeny QIANG JI,! MARK A. NORELL,”? PETER J. MAKOVICKY,*? KE-QIN GAO,?* SHU’AN JIA AND CHONGXI YUAN? ABSTRACT A new ornithomimosaur from the Yixian Formation of Liaoning Province People’s Republic of China is described. These beds are near the Jurassic-Cretaceous boundary. This specimen is interesting because it has several primitive characters for ornithomimosaurs such as teeth and a short first metacarpal. This taxon is placed in a phylogenetic analysis of Coelurosauria and shown to be near the base of the ornithomimosaur clade. Using this phylogeny we comment on the biogeographic history of this group. INTRODUCTION and often preserving soft-part anatomy, these fossils can be frustrating because of a lack of Spectacular fossils from China’s Liaoning three-dimensional preservation. Furthermore, Province have become commonplace in the theropod remains from Liaoning only in- last few years (Ji and Ji, 1996; Ji et al., 1999; clude the maniraptoran groups Dromaeosaur- Hou, 1997; Gao et al., 2000). However, most idae (Xu et al., 1999b, 2000), Oviraptorosau- of these are nearly two-dimensional fossils ria (Ji et al., 1998, Xu et al., 2002a), Troo- found in paper shales that represent ancient dontidae (Xu et al., 2002b), and Segnosaur- pond and lake deposits. Although beautiful idae (Xu et al., 1999a) and the more ' Department of Earth Sciences, Nanjing University, 22 Hankou Road, Nanjing 210093, and Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing 100037 China. e-mail: [email protected] ? Division of Paleontology, American Museum of Natural History. e-mail: [email protected] 3 The Field Museum, 1400 S. Lake Shore Drive, Chicago IL, 60660. e-mail: pmako@ vfieildmcuskeumy.or g 4 School of Earth and Space Sciences, Peking University, Beijing 100871, China. e-mail: [email protected]. edu.cn 5 China University of Geosciences, Beijing 100083, China. Copyright © American Museum of Natural History 2003 ISSN 0003-0082 2 AMERICAN MUSEUM NOVITATES NO. 3420 primitive compsognathid Sinosauropteryx head above the torso. The distal hindlimbs, (Chen et al., 1998). Here we describe a new distal tail, and the forelimbs (except for part ornithomimid dinosaur, the first from the of the right hand) and the pectoral girdle are Liaoning beds, and comment on its relation- missing. The head is crushed, exposing the ships to other ornithomimids. left side obliquely. Ornithomimid dinosaurs were the first ETYMOLOGy: Shenzhou is the ancient name toothless nonavian dinosaurs to be described of China, orientalis refers to the east. (Marsh, 1890). Consequently, much has been Type Loca.ity: Sihetun fossil site, Bei- written concerning their relationships and piao, Western Liaoning, China (fig. 3). diet (Gauthier, 1986; Holtz, 1994; Sereno, GEOLOGICAL OCCURRENCE: The holotype 1997, Kobayashi et al., 1999; Norell et al., comes from the lowermost, fluvial part of the 2001b). Although toothed forms have been Early Cretaceous Yixian Formation. These recovered (Pérez-Moreno et al., 1994; Bars- rocks are older than 128 mybp and younger bold and Perle, 1984), these are either diffi- than 139 mybp (Swisher et al., 2002); older cult to place phylogenetically or are extreme- dates have been reported (Lo et al., 1999). ly fragmentary. DIAGNOSIS: an ornithomimosaur distin- Local farmers collected the specimen, and guishable from all others except Harpymimus some of the elements were clearly lost during in having teeth restricted to the anterior den- the excavation process. It is apparent that tary. Shenzhousaurus orientalis shows prim- both the tail and the forelimbs were present itive characters not found in advanced orni- in adjoining blocks (fig. 1). When the spec- thomimosaurs, like a straight ischium and a imen was collected it was cracked into two postacetabular process that is gently curved blocks, shattering many bones and leaving rather than truncated. Shenzhousaurus orien- parts of the skeleton in each block. During talis is distinguishable from Pelecanimimus the preparation process parts of the counter by the tooth distribution pattern and the block were glued to the main slab, and the primitive configuration of the hand where sediment surrounding the bones was re- digit I is shorter than digits IJ and III. moved. In other cases individual elements were prepared completely free of the counter DESCRIPTION slab and affixed to the main slab. This prep- SKULL aration process resulted in a single block with the specimen preserved in bas-relief The left side of the snout is well pre- (fig. 2). served, whereas the right side is crushed and displaced postmortem (fig. 4). The orbital INSTITUTIONAL ABBREVIATIONS and braincase regions are flattened and the left frontal and parietal are flipped under the AMNH~ American Museum of Natural History right. The left squamosal is isolated and lies IGM Institute of Geology Mongolia adjacent to the caudal end of the lower jaw. NGMC_ National Geological Museum of China ROM Royal Ontario Museum The left mandible appears to be intact and well preserved. The premaxilla has a relatively short body, SYSTEMATIC PALEONTOLOGY and the premaxillary buccal margin is only THEROPODA MARSH, 1881 as long as the external naris. The internarial COELUROSAURIA VON HUENE, 1914 bar is dorsoventrally flat and is formed main- ly by the premaxillae, with only a minor con- ORNITHOMIMOSAURIA BARSBOLD, 1976 tribution from the nasals. The posterodorsal ORNITHOMIMINAE SERENO, 1998 process of the premaxilla is elongate as in other ornithomimids, and it overlaps the na- Shenzhousaurus orientalis, new taxon somaxillary suture well posterior to the cau- TYPE SPECIMEN: NGMC (National Geolog- dal end of the naris. It is broadest at its base ical Museum of China) 97-4-002. but tapers caudally. Although incomplete dis- MATERIAL: A partial skeleton preserved on tally, it does not appear to have reached the a sandstone block in a death pose with its level of the antorbital fossa. The labial sur- 2003 JI ET AL.: A TOOTHED ORNITHOMIMOSAUR 3 Fig. 1. NGMC 97-4-002 before preparation. + AMERICAN MUSEUM NOVITATES NO. 3420 Fig. 2. The holotype skeleton of Shenzhousaurus orientalis as preserved on the main block, with parts in counterblock reattached. Abbreviations: g, gastralia; ga, gastroliths; If, left femur; li, left ilium; lis, left ischium; Ip, left pubis; lu, ungual of left hand; pb, pubic boot; r-dl, right digit I; r-dI, right digit II; r-dIUJ, right digit II; rf, right femur; rp, right pubis. 2003 JI ET AL.: A TOOTHED ORNITHOMIMOSAUR , larger antorbital and a smaller accessory fenestra. The rostral 40% of the maxilla lies anterior to the antorbital fenestra and has a flat lateral surface marked only by a few foramina, presumably for neurovascular trans- mission. The buccal margin is slightly sinuous in this region and rises gently toward the front. The buccal margin of the maxilla is Beipiao Shenyang very shallow beneath the antorbital fossa. A . * *Sihetun ® large maxillary palatal shelf is visible along Chaoyang *Yixian the anterior two-thirds of the antorbital fossa. Liaoning The fossa appears to be bordered by the nasal Province for a short stretch dorsal to the antorbital fenestra, although the maxilla is not complete in this region. Posterior to this the dorsal 50 100 km edge of the antorbital fenestra is bordered by the elongate anterior ramus of the lacrimal. The accessory fenestra perforates a de- pressed medial lamina of the maxilla that walls off the anterior third of the antorbital Fig. 3. The fossil locality. fossa medially. The posterior part of this lamina, which forms the interfenestral bar, bears dorsal and ventral embayments along face of the subnarial part of the premaxilla the posterior border, perhaps indicating some is marked by a few neurovascular foramina, type of interfenestral connection as in troo- the largest of which is located at the base of dontids (Norell et al., 2000; Makovicky et the internarial bar. al., 2003). The maxilla is very elongate and bears a The jugal is poorly preserved, and articu- large antorbital fossa that is perforated by a lar contacts with the maxilla and lacrimal che pli 9) eee RSV 2,0r eas lpmx Imx Fig. 4. Close-up of the left side of the skull of Shenzhousaurus orientalis. Abbreviations: ch, choana; fr, frontal; Id, left dentary; Il, left lacrimal; Imx, left maxilla; In, left nasal; lpmx, left premaxilla; Isq, left squamosal; mxf, maxillary fenestra; plr, palatine recess; rn, right nasal. 6 AMERICAN MUSEUM NOVITATES NO. 3420 cannot be traced. The orbital portion of the tending anteriorly around the caudal end of jugal is very slender, and the anteroventral the supratemporal fenestra, a rostroventrally corner of the orbit appears to have had a directed quadrate process that adheres to the right-angled rather than a rounded shape. anterior edge of the quadrate shaft, and a Posteriorly, the jugal is obscured by other el- short lateral process. The intertemporal pro- ements. cess of the squamosal is longer than the me- The lacrimal bears an elongate anterior dial supratemporal process. The dorsal sur- process that borders the caudal half of the face of the squamosal between these two pro- antorbital fenestra dorsally. A short, pointed cesses is incised by a caudal extension of the posterior process is present on the lacrimal. supratemporal fenestra, bordered by a sharp It may have inserted into a notch on the dor- rim, as in Gallimimus (IGM 100/1133). The sal surface of the prefrontal as in Gallimi- quadrate process of the squamosal is trian- mus, but the prefrontal cannot be identified. gular. The posterolateral process extends pos- Neither large fossae nor hornlike structures terior to the quadrate articulation, but its are present on the lacrimal. length cannot be determined because it is A short section of the right postorbital is overlapped by a disarticulated piece of the exposed in dorsal view, and it forms the an- braincase. The articulation with the quadrate terior part of the intertemporal bar. It is rel- is not exposed in lateral view in Shenzhou- atively massive compared to the postorbital saurus orientalis, as it is in Gallimimus contribution to the intertemporal bar in other (IGM 100/1133) and Ornithomimus. ornithomimid taxa. The postorbital of Shen- Parts of the palate, including parts of both zhousaurus orientalis does not reveal the palatines and possibly the left pterygoid, are characteristic anterodorsal curvature seen in exposed. The palatine bears two anteriorly maniraptorans. elongate processes that almost enclose the in- The right frontal is exposed in dorsal view ternal choana. The medial, interchoanal pro- (fig. 5). A coronally directed crack extending cess is longer than the lateral one, in contrast through the frontal just anterior to the artic- to Allosaurus (Madsen, 1976), but similar to ulation of the postorbital may be the result Sinraptor (Currie and Zhao, 1993) and Dei- of dorsoventral crushing of a strongly flexed nonychus (Witmer, 1997), and it extends at part of the frontal. The frontals of other or- least as far rostrally as the interfenestral bar. nithomimid taxa are domed near the poste- The interchoanal process of the left side rises rior part of the orbit, forming a flexure be- dorsomedially to meet its counterpart on the tween the flat parts of the frontal and parie- right side and form the interchoanal bar, pos- tals. Anterior to the extensive orbital rim, the sibly with participation of the pterygoids. lateral edge of the frontal is sinuous and the The interchoanal bar is unlike the large, lo- medially inflected portion may mark a de- bate structure of Allosaurus (Madsen, 1976), pression for the reception of a prefrontal. but is more slender and curves anteriorly The parietals appear paired and unfused. from the posterior end of the choana as in The dorsal surface of the parietal is flat and Velociraptor (Barsbold and Osmdolska, lacks a sagittal crest. A laterally concave 1999). The dorsal surface of the palatine flexure marks the medial edge of the supra- bears a deep fossa, the palatine recess (Wit- temporal fenestra and separates the dorsal surface of the parietal from the lateral surface mer, 1995), near the base of the maxillary that forms parts of the adductor chamber. The process just rostral to the level of the lacrimal frontoparietal suture is sinuous in dorsal (fig. 5). The palatine recess in Shenzhousau- view, as in Gallimimus (Osmdlska et al., rus orientalis is in a similar position to pal- [972). atine recesses observed in dromaeosaurs The left squamosal is disarticulated and such as Deinonychus (Witmer, 1995: fig. 32) lies adjacent to the caudal end of the left and Velociraptor (IGM 100/982). The recess mandible. It is exposed in lateral view, and invades the palatine body mediodorsally in the proximal end of the quadrate is preserved Shenzhousaurus orientalis rather than poster- in articulation with the squamosal. The squa- odorsally as in the two dromaeosaurid taxa. mosal is tetraradiate, with two processes ex- Part of the pterygoid process of the palatine 2003 JI ET AL.: A TOOTHED ORNITHOMIMOSAUR wi mena Fig. 5. Closeup of braincase. Abbreviations: dv, dorsal vertebra; f, frontal; Ip, left prootic, Is?, left laterosphenoid, Isa, left surangular, Isq, left squamosal; 1, rib. is exposed within the orbit, posterior to the ectopterygoid to this may represent a part of lacrimal. the pterygoid. The hooked jugal process is the only vis- A large, crushed bone that overlaps the ible part of the ectopterygoid and is exposed posterior part of the mandible may be a la- within the orbit slightly posterior to the pter- terosphenoid. We interpret a large broken el- ygoid process of the palatine. A narrow sliv- ement posterior to the right parietal as the left er of bone dorsal to the jugal process of the prootic with its anterior surface (laterosphen- 8 AMERICAN MUSEUM NOVITATES NO. 3420 ‘ 4 2 aa y . et5 a - fm 5 a iT th fena- ff). AidR C a ny = Fig. 6. The dentition of Shenzhousaurus orientalis as preserved in the left dentary. oid articulation) facing upward (fig. 5). A splintlike process overlapping the dentary. well-delimited depression on the lateral sur- Fragments of the angular are exposed along face appears to be the dorsal tympanic recess. the ventral border of the external mandibular Medial to it, the posterior border of the floc- fenestra. The glenoid and retroarticular pro- cular recess is visible. Part of the border of cess are exposed. A flattened area just rostral a large foramen, which is surrounded by a to the glenoid may correspond to the dorsal wide fossa on the lateral surface of the brain- trough or sulcus seen on the surangular of case, is visible anteroventral to the floccular many theropods, including Velociraptor, Ty- recess and is here interpreted as the exit for rannosaurus, and Ornitholestes. As in other the trigeminal nerve. ornithomimids, an everted tab forms the an- The complete left mandible is preserved, terolateral margin of the glenoid. In these but much of the postdentary region is cov- taxa, such as Gallimimus, this tab articulates ered by the unidentifiable braincase element. with an elongate, curved extension of the lat- The dentary is elongate but shallow and eral quadrate condyle. The retroarticular pro- spans about two-thirds the length of the jaw. cess is crushed, but it appears to be expanded The dentary is deepest below the middle of medially. the antorbital fenestra. It tapers gently rostral "TEETH to this point, up to a point just posterior to the toothrow, where it deflects rostroventral- Six minute tooth crowns and a broken root ly. The buccal margin is deflected anteroven- are preserved at the deflected anterior tip of trally at the symphysis, as in other ornithom- the left dentary. Gaps between the preserved imosaurs except Pelecanimimus (Pérez-Mo- teeth suggest the presence of one or two ad- reno et al., 1994). The lateral surface of the ditional tooth positions. The teeth are conical and project slightly anteriorly. They do not dentary is pocked by three roughly linear rows of neurovascular foramina (fig. 6). have a constriction between the root and crown. A thin layer of enamel is preserved These extend posteriorly to the end of the on the teeth. There is no trace of either ca- abbreviated toothrow. Farther caudally, a rinae or serrations. shallow groove follows the dorsal margin of the dentary until it reaches the rostrodorsal AXIAL SKELETON process of the surangular. As in other ornithomimosaurs, the external CERVICAL VERTEBRAE mandibular fenestra is reduced. It is bordered No cervical vertebrae can be identified on dorsally by the surangular that has a long, the specimen. JI ET AL.: A TOOTHED ORNITHOMIMOSAUR 9 thomimus (Makovicky, 1995), Gallimimus (Osmolska et al., 1972), Struthiomimus, and Archaeornithomimus (Makovicky, 1995). Sl — 7 The ilium appears to be slightly displaced ¥ i from the sacrum, thus exposing the trans- 4 a verse processes of the last sacral in lateral Biaret view. As in other ornithomimosaurs, the fi ue f transverse processes of this element flare F i widely distally where they meet the medial | (a ee =i i he border of the brevis fossa, and they may have is te - ‘ —_— : contributed to the insertion area of the cau- 1cm difemoralis brevis musculature. The neural Fig. 7. Dorsal vertebrae of Shenzhousaurus spine of the last sacral appears to have been orientalis. freestanding, but it cannot be determined whether the neural spines of the remaining sacrals formed a lamina as in some other or- DORSAL VERTEBRAE nithomimosaurian specimens. An articulated series of the last eight dor- CAUDAL VERTEBRAE sal vertebrae are preserved in articulation with the sacrum. The centra are elongate and A section of the tail comprising 15 artic- spool-shaped and are devoid of pneumatic ulated caudal vertebrae is preserved, curving foramina (fig. 7). The anteriormost centrum, posterodorsally from the sacrum (fig. 8). All which is broken anteriorly, bears a faint keel the preserved caudals possess transverse pro- ventrally. Neural arches bear large pneumatic cesses or traces thereof, indicating that the infraprezygapophyseal, infradiapophyseal, transition point lies distal to the preserved and infrapostzygapophyseal fossae below the section of the tail. Centrum length increases transverse processes. The infraprezygapo- distally in the preserved section, whereas physeal fossae are especially large and ap- centrum height decreases distally. pear to extend into the prezygapophyses. The The transverse processes are distally ex- neural spines are long, tall anteroposteriorly panded and backswept. Their distal ends are expanded distally. The neurocentral sutures rounded. In the second and third caudal ver- are fused but not obliterated. In no case is a tebrae, a thin lamina extends anteriorly from neural arch separated from its corresponding the transverse process on to the lateral face centrum. of the prezygapophysis, where it forms a dis- Parts of 10 dorsal ribs are preserved on the tinct ridge bounding a shallow fossa. This block, but none is complete. Two left ribs, connection between the transverse process which probably articulated with the fourth and prezygapophysis is also present in Or- and fifth dorsals in the preserved series, have nithomimus. The neural spines of the first 12 anteroposteriorly flared shafts as in other or- vertebrae are obscured by transverse pro- nithomimids (Barsbold and Osmdlska, cesses. Those of the remaining three caudals 1990). are parallelogram-shaped and lean posteriorly, extending beyond the caudal end of SACRAL VERTEBRAE their respective centra. Parts of five sacral vertebrae are exposed CHEVRONS but are partly obscured by the pelvic elements and the left femur. The centra appear The first chevron is situated between the to be fused, but the sutural lines are still ev- first and second caudals. It is rod-shaped, but ident. A constricted pit is visible on the ex- its length is indeterminate, as the second posed lateral surface of both the third and chevron covers it distally. The second to fourth sacrals. Such noninvasive depressions fifths chevron are very elongate, slender, and are also present on the sacral vertebrae of rod-shaped with a slight posterior curvature other ornithomimid taxa, including Orni- that becomes more pronounced in more dis- 10 AMERICAN MUSEUM NOVITATES NO. 3420 Fig. 8. Anterior caudal vertebrae of Shenzhousaurus orientalis. tal elements. Posterior to this, the chevrons may have only comprised this medial ele- become progressively wider, mediolaterally ment compressed, shorter, and more hooked. The last two chevrons are strongly hooked and APPENDICULAR SKELETON end in a point distally. PELVIS The pelvis is present in semiarticulation GASTRALIA although some elements were shattered when Parts of eight gastral arches from the right the slab was split. The ilium is about equal side are preserved, but only one preserves in length to the pubis, and the ischium is only both the complete medial and lateral seg- slightly shorter (see table 1). ments (fig. 9). The medial segment has an Most of the exposed dorsal surface of the expanded and dorsoventrally compressed ilium is shattered, as it lay on the contact midline end. It tapers distally and is over- between the slab and counterslab (fig. 10). lapped anteriorly by the lateral element. The Nevertheless, it can be determined that the two elements are approximately equal in anterior and posterior blades are roughly length, unlike those of higher ornithomimids, equivalent in length and that the iliac blade in which the medial elements are longer. The was dorsoventrally low. The ilia covered six dorsal ends of the rodlike lateral elements are vertebrae, less than in Gallimimus and Or- slightly expanded and curve dorsally. The nithomimus (Barsbold and Osmolska, 1990). last gastral element is three times wider than Apparently the ilia met at the midline as in the preceding segments. The last gastral arch other ornithomimids (Makovicky et al., in