A NEST OF PROTOCERATOPS ANDREWSI (DINOSAURIA, ORNITHISCHIA)

Journal of Paleontology, 85(6), 2011, p. 1035–1041 Copyright ’ 2011, The Paleontological Society 0022-3360/11/0085-1035$03.00 A NEST OF PROTOCERATOPS ANDREWSI (DINOSAURIA, ORNITHISCHIA) D. E. FASTOVSKY,1 D. B. WEISHAMPEL,2 M. WATABE,3 R. BARSBOLD,4 KH. TSOGTBAATAR,5 AND P. NARMANDAKH6 1 Department of Geosciences, University of Rhode Island, Kingston, RI 02881, USA, ,[email protected].; 2Center for Functional Anatomy and Evolution, Johns Hopkins University, Baltimore, Maryland 21205, USA, ,[email protected].; 3Hayashibara Museum of Natural Sciences, 2-3. Shimoishii-1, Okayama 700-0907, Japan, ,[email protected].; 4Director, Paleontological Center, Mongolian Academy of Sciences, Peace Avenue 63 Ulaanbaatar 210351, Mongolia, ,[email protected].; 5Paleontological Center, Mongolian Academy of Sciences, Peace Avenue 63 Ulaanbaatar, Ulaanbaatar 210351, Mongolia, ,[email protected].; and 6Paleontological Center, Mongolian Academy of Sciences, Ulaanbaatar 210351, Mongolia ABSTRACT—A remarkable specimen of the small neoceratopsian dinosaur Protoceratops andrewsi (Late Cretaceous, Mongolia) reveals the first nest of this genus, complete with fifteen juveniles. The relatively large size of the individuals and their advanced state of development suggests the possibility that Protoceratops juveniles remained and grew in their nests during at least the early stages of postnatal development. The nest further implies that parental care and sociality are phylogenetically basal behaviors in Ceratopsia. Finally, it reaffirms the conclusion that Protoceratops lived (and died) in the sandy aeolian dune fields of the central Asian craton. INTRODUCTION Tugrikin Shire to represent an aeolian dune field, dominated and juvenile material are now during Cretaceous time by west-southwest winds. Extensive E MBRYONIC, HATCHLING, known for nearly all major dinosaur groups (Ornitho- poda, Ceratopsia, Prosauropoda, Sauropoda, and Thero- bioturbation preserved along bounding surfaces, as well as the vertebrate fossil wealth of this locality—mainly articulated poda). In some cases, based largely on the degree of specimens of the ceratopsian genus Protoceratops—has ossification of the long bones, the young are thought to have suggested to many authors that the Tugrikin Shire dune field left the nests immediately after hatching (Horner, 1984; was a region of extraordinary ancient biotic activity (Ishii Weishampel and Horner, 1986; Horner and Weishampel, et al., 2000; Gao and Norell, 2000; Dashzeveg et al., 2005; 1988; Chure et al., 1994). In contrast, some ornithischian taxa Turner et al., 2007). Descriptions of the petrology and aeolian are thought to have had nest-bound hatchlings with parental sedimentary geology of Tugrikin-Shire, as well as a description care, based on long-bone ossification and size disparities in of aspects of the taphonomy of some of the many Protocera- concert with the preservation of inferred nests (Horner and tops specimens found there, are found in Fastovsky et al. Makela, 1979; Horner and Weishampel, 1988; Horner, 2000; (1997). Horner et al., 2001). MPC-D 100/530 (Weishampel et al., 2000) consists of a Here we report on an articulated juvenile assemblage of the series of fifteen fully articulated, aligned skeletons of juveniles, dinosaur Protoceratops cf. andrewsi Granger et Gregory 1923 with the skulls all facing east-southeast. Six complete (MPC-D 100/530). The assemblage is interpreted as associated individuals are closely appressed along the well-defined within a nest. Along with aggregations of Psittacosaurus from (eastern) margin, suggesting an originally circular shape about Early Cretaceous deposits of Liaoning, China (Meng et al., 70 cm in diameter (Fig. 2). All individuals show juvenile 2004; Erickson et al., 2009), this specimen reaffirms the idea characteristics including proportionately large orbits, short that young dinosaurs remained in the nest for a significant snouts, and an absence of adult characteristics such as time after hatching, and therefore that parental care was likely prominent horns and large frills (Dodson, 1996; Dodson et involved. This in turn suggests that parental care was a basal al., 2004). At least ten are complete (Fig. 2). behavioral characteristic of ceratopsian dinosaurs. SYSTEMATIC PALEONTOLOGY LOCALITY AND PRESERVATION Suborder CERATOPSIA Marsh, 1890 Mongolian-Japanese expeditions collected MPC-D 100/530 Infraorder NEOCERATOPSIA Sereno 1986 from the Upper Cretaceous Djadokhta Formation of central Family PROTOCERATOPSIDAE Sereno, 2000 Asia (Berkey and Morris, 1927; Eberth, 1993; Loope et al., Genus PROTOCERATOPS, Granger et Gregory 1923 1998; Dashzeveg et al., 2005; Barsbold et al., 2008; Dingus PROTOCERATOPS cf. ANDREWSI Granger et Gregory 1923 et al., 2008) exposed at Tugrikin Shire, O¨ mno¨gov’, Mongolia Specimen.—MPC-D 100/530, currently housed at the Pale- (Fig. 1). There, the Djadokhta Formation consists almost ontological Center of the Mongolian Academy of Sciences, exclusively of weakly cemented, fine-grained, very well-sorted, Ulan Baatar, Mongolia. very large-scale cross-stratified sandstones. The dip slopes of Locality and horizon.—Djadochta Formation, Tugrikin the huge foresets, which in plan view are arcuate and extend ¨ mno¨gov’, Mongolia. shire, O for distances .100 m (Fastovsky et al., 1997; Saneyoshi and Description.—Skulls preserve nearly all cranial elements Watabe, 2007), are oriented at 52.5u; SD 4.71u; n5100 (see (Fig. 3), including the facial skeleton, braincase, palate, and also Fastovsky et al., 1997, reporting a mean dip orientation uncommonly, palpebrals and sclerotic rings. In contrast to of 76.8u; R50.929; n524). On the basis of textural maturity, adults, the snout is short, blunt and dorsoventrally low. The the large scale and high angle of the cross-stratification, and small rostral bone is situated rostroventrally in the snout mm-scale coarsening upwards sequences observed within the region, close to the external nares. Both features are located cross-strata, Fastovsky et al. (1997) intepreted the deposits at farther forward in adults. There is no indication of a nasal 1035 Journal of Paleontology pleo-85-06-02.3d 17/8/11 08:47:18 1035 Cust # 11-008R 1036 JOURNAL OF PALEONTOLOGY, V. 85, NO. 6, 2011 FIGURE 1—Topographic map of Tugrikin Shire showing geographic and stratigraphic position of MPC-D 100/530. The crescentic form east southeast of the outcrop is a modern barchan dune. Grain size abreviations are si5silt; fss5fine sandstone; mss5medium sandstone. Inset map of Mongolia indicates location of Tugrikin Shire (TS). eminence or horn core; characteristic of adult animals moderately tall neural arches and ossified tendons associated (Makovicky et al., 2007). The elliptical antorbital fossa, with them in adult Protoceratops; we note, however, neural characteristic of Protoceratops, has similar relative position spines are observed in an embryonic neoceratopsian bearing a on the rostrum to that of adult specimens (Brown and braincase resembling that of Protoceratops (Balanoff et al., Schlaikjer, 1940; Dodson, 1976); however, it has a rostrodor- 2008). sal long axis, unlike the adult caudodorsal orientation. The Consistent with their general immaturity, all of the ends of orbits are close to each other and proportionately larger than the long bones are composed of poorly-defined, spongy bone. in adult Protoceratops. Mean skull length is 43 mm (Fig. 3), a All of the elements of the appendicular skeleton bear poorly- number that is signficantly smaller than the skull lengths of defined articular surfaces. Complete forelimbs, down to the adult specimens of Protoceratops that have been recovered from unguals, are preserved in a number of individuals (Fig. 4.2). In Tugrik and elsewhere, but larger than the smallest specimens all cases, the elements are more gracile than in adults. A low known to have been referred to Protoceratops (e.g., IGM100/ spine crosses from craniodorsal to the supraglenoidal ridge of 3003; personal commun., M. Norrell and P. Makovicky). the narrow scapula, as in adults. The coracoid is not visible in The width of the supratemporal fenestra is proportionately any of the individuals, due to the prone position of the much greater than in adult individuals. The rostromedial skeletons. The humerus bears a distinct, but low deltopectoral extension of the supratemporal fenestra onto the frontal and crest lateral on the upper half of the shaft and the long axis of parietal is very faintly developed in these juvenile animals, in the bone deviates medial from the midshaft onward. The contrast to adults. The frontoparietal suture is clearly seen at hemispheric head is located more to the caudal surface of the the level of the caudal edge of the orbit. Along this suture are humerus. The ulna is longer than the radius and bears a large small fronto-parietal depressions. The frill is very short with olecranon process. The carpus is unossified. The manual parallel edges compared to the expanded and caudally flared digital formula is ?-2-3-4-?-?. Hoof-like unguals terminate each adult condition. The frill margin is straight, and tapers to a digit of the hand and foot. The length of the forelimb is 67% thin edge. Fenestrae are not developed in the frills of these that of the hindlimb, closer to the condition in basal juveniles, although they become well-developed in adult neoceratopsians than in Psittacosaurus spp. Protoceratops. The ilium is proportionately dorsoventrally low, much more Postcranially, these juveniles have 12 dorsal vertebrae and so than in adults, in keeping with incomplete ossification at 12 pairs of ribs (Fig. 4.1). Vertebral ossification is incomplete this early life stage. It is difficult to determine whether the and neural arches and spines are not preserved in any of the preacetabular process is incipiently everted, as it is in adult skeletons, a condtion that contrasts markedly with the Protoceratops andrewsi. The long, slender, and straight Journal of Paleontology pleo-85-06-02.3d 17/8/11 08:47:20 1036 Cust # 11-008R  FASTOVSKY ET AL.—PROTOCERATOPS NEST 1037 FIGURE 2—Specimen photograph of MPC-D 100/530 showing complete nest and all individuals of Protoceratops cf. andrewsi (Granger and Gregory, 1923). Line drawing highlighting outlines of individuals. North arrow in upper right-hand corner. Scale in cm. ischium lacks an obturator process. The pubis has not yet been For all that, however, several characters suggest Protocera- exposed (Fig. 4.3). tops affinities including an eliptical antorbital fossa, median The hindlimb is also gracile (Fig. 4.3). The femur is bowed keel on the frill, small fronto-parietal depressions (Dong and and a modest cleft separates that greater from the cranial Currie, 1983; You and Dodson, 2004), and hoof-shaped pedal trochanters. A low, pendant fourth trochanter is located just unguals (Sereno, 2000). Within Protoceratops, two species are proximal to the midshaft. The tibia and fibula are 130% the recognized: P. andrewsi (Granger and Gregory, 1923) and length of the femur, a greater ratio than in adults. The P. hellinkorhinus (Lambert et al., 2001). Of the characters astragalus appears on the medial half of the distal tibial that distinguish the latter from P. andrewsi—the absence of condyle. Beneath the mesotarsal joint are at least three poorly- premaxillary teeth, two nasal horns, well-developed fronto- defined ossified distal tarsals. Overall, the pes is compact and parietal depressions, and a forwardly curved frill (You and elongate. The metatarsals and phalanges are well-preserved Dodson, 2004)—the presence or absence premaxillary teeth and articulated. Metatarsal V is very small. The pedal digital has the potential to diagnose; the other characters are simply formula is 2-3-4-5-0 and the unguals are blunt and hoof-like. not well developed within these juvenile skeletons. In the case Diagnosis.—Sereno (2000) noted that ‘‘generic and specific of the teeth, however, insufficient preparation precludes diagnoses for Protoceratops … do not include any derived positive identification of the character, even presuming that features because the skeleton is plesiomorphic … at the level of at this juvenile stage they would have erupted. There are, Neoceratopsia’’ (p. 489). The issue of diagnosis is further however, no reasons to preclude a specific assignment to P. complicated because many of the osteological characters that andrewsi, and given the fact that adult Protoceratops andrewsi are used to characterize the adults (e.g., You and Dodson, 2004) are the only ceratopsians known from Tugrikin-shire (Brown are either muted or not developed in these juveniles. In addition and Schlaikjer, 1940; Dodson, 1976; Dong and Currie, 1993; to indicating their immature status, several features of the skull, Lambert et al., 2001), we tentatively refer all of the individuals including the relatively flat, straight snout and the short, in MPC-D 100/530 to P. cf. andrewsi. parallel-sided frill, also constitute the plesiomorphic condition for Ceratopsia (Balanoff et al., 2008). In these features, these DISCUSSION ceratopsians resemble the adults and juveniles of more basal Nest.—While ideal criteria for identifying dinosaur nests members of this clade, like Psittacosaurus spp. (Long and may not all be preserved in MPC-D 100/530 (Chiappe et al., McNamara, 1995; Meng et al., 2004; Zhao et al., 2007), 2004), the shape and size distribution of the assemblage of Liaoceratops, and Auroraceratops (You and Dodson, 2004). individuals in MPC-D 100/530 argue for its being a nest. First, Journal of Paleontology pleo-85-06-02.3d 17/8/11 08:47:20 1037 Cust # 11-008R 1038 JOURNAL OF PALEONTOLOGY, V. 85, NO. 6, 2011 FIGURE 3—Skulls from two different individuals of Protoceratops cf. andrewsi (Granger and Gregory, 1923) in MPC-D 100/530. 1, left three-quarter view; 2, top view. Scale in cm. the animals in the assemblage are young, the same size, and well-developed, curved margin in the sandstone at the edge of show the same degree of ontogenic development; they are thus the assemblage to be inconsistent with this hypothesis. For reasonably interpreted to be the same age, such as would be these reasons, therefore, we prefer the interpretation of this found within a single clutch in a nest. Second, the distinctive assemblage as a nest of individuals. curved margin on the eastern side of the specimen (Figs. 2, Our best inference is that these individuals, although young, 4.1) is as might be expected in a circle- or oval-shaped nest are not neonates. First, no eggshell material was found with (contra Thulborn, 1992). That margin and the distribution of the specimen, as might be predicted if the animals were freshly the individuals in MPC-D 100/530 even suggest an approxi- hatched. Eggshell is common at this locality so it is unlikely mate diameter for the feature (see above). that it would have disappeared diagenetically if present. An alternative hypothesis is that this specimen is simply More significantly, however, the juveniles described here are some kind of aggregate of individuals, perhaps brought approximately 60% larger than an a less well-ossified, together during a sandstorm (see below). If such were the undescribed specimen from the same locality and referred to case, it would be unlikely that the individuals be exclusively the same taxon (IGM100/3003; M. Norrell and P. Makovicky, juveniles of the same age. Moreover, we view the presence of a personal commun.). We infer, therefore, that the animals Journal of Paleontology pleo-85-06-02.3d 17/8/11 08:47:30 1038 Cust # 11-008R  FASTOVSKY ET AL.—PROTOCERATOPS NEST 1039 FIGURE 4—Protoceratops cf. andrewsi (Granger and Gregory, 1923) juveniles in situ from from MPC-D 100/530. 1, ten individuals showing axial skeletons; curved eastern margin of nest visible at left side of figure; 2, right forelimb with scapula (s), humerus (h), radius and ula (ru), and manus (m) clearly visible; 3, pelvis showing paired anterior-directed iliac blades (il); posterior-facing ischia (is); hindlimb in articulation with pelvis, including femur (f), tibia and fibula (tf), and pes (p). Note blunt hoof-bearing ungual phalanges capping digits and visible on I and IV (u). Scale in cm. described here grew after hatching. Growth at the nest implies paleoenvironment in which the juveniles were found shows a life history for Protoceratops andrewsi that involved some clear evidence of WSW prevailing winds (see above; Fastovsky degree of of nest-bound parental support. et al., 1997). The axial skeletons are oriented subparallel to Mortality.—MPC-D 100/530 provides dramatic evidence of wind direction, with the heads pointing ESE (long axis of the the last minutes of the lives of the juveniles it preserves. The skulls 110.2u; SD 4.45u; n512; long axis of the ilia: 103.1u; SD Journal of Paleontology pleo-85-06-02.3d 17/8/11 08:47:43 1039 Cust # 11-008R 1040 JOURNAL OF PALEONTOLOGY, V. 85, NO. 6, 2011 4.63u; n 5 10). The forelimbs of most of the individuals are respectively, of MPC-D 100/530. Drs. M. Norell (American retracted and manual portions are directed caudally. In Museum of Natural History and P. Makovicky (Field contrast with the forelimbs, hindlimbs are fully retracted to Museum of Natural History) read and edited earlier drafts lie parallel to the long axis of the body (e.g., Fig. 4). The of this manuscript; their contributions are gratefully acknowl- arrangement of the limbs suggests that the animals tried to edged. We are grateful for thoughtful, constructive reviews move their bodies forward in the then-loose sand, away from by B. Chinnery, F. Jackson, and D. Varricchio. Funding was the prevailing west-southwest wind, possibly even climbing provided by the Department of Geosciences, University of over one another prior to or during burial. Rhode Island, and by the Hayashibara Museum of Natural It has been proposed that the spectacular fossil preserva- Sciences. This is Hayashibara Museum of Natural Sciences tion found at Tugrikin Shire was caused by rapidly migrating Contribution no. 42. dunes and associated sandstorms (Jerzykiewicz et al., 1993; REFERENCES Fastovsky et al., 1997). In this model, the edge along the lee side of the nest would have been the area where the air was ANDREWS, R. C. 1932. The New Conquest of Central Asia. American Museum of Natural History Press, New York, 678 p. the freest of sand and therefore available to the young ANDREWS, R. C. 1933. Explorations in the Gobi Desert and Nomad Life dinosaurs. Consequently, they may all have struggled to and Fossil Treasures of Mongolia. National Geographic, 63:653–716. reach this part of the nest. In this case, slipfaces preserved just BALANOFF, A. M., M. A. NORELL, G. GRELLET-TINNER, AND M. R. above the nest itself (see Fig. 1) reinforce this model of LEWIN. 2008. Digital preparation of a probable neoceratopsian episodic storm-driven dune migration in a dynamic, unstabi- preserved within an egg, with comments on microstructural anatomy of ornithischian dinosaurs. Naturwissenschaften, 95:493–500. lized sandy environment. BARSBOLD R., D. BADAMGARAV, KH. TSOGTBAATAR, SH. GANSUKH, Basing their analysis on the Djadokhta Formation as TS. BAZARRAGCHAA. 2008. Cretaceous non-marine sediments and exposed in the Ukhaa Tolgod locality, Loope et al. (1998) dinosaur localities in Ulaan Nuur depression, south Mongolia. IGSP proposed a grain flow model for Djadochta mortality, in 507 Fieldtrip Guidebook, p. 1–24. which rainstorms caused the catastrophic mobilization of sand BERKEY, C. P. AND F. K. MORRIS. 1927. Geology of Mongolia. In Natural History of Central Asia, Vol. II. American Museum of Natural down the faces of stabilized alluvial fans. These produced History Press, New York, 427 p. structureless sandy lithofacies such as those associated with BROWN, B. AND E. M. SCHLAIKJER. 1940. The structure and relationships the spectacular vertebrate preservation of Ukaa Tolgod and of Protoceratops. Annals of the New York Academy of Sciences, other Djadochta localities (Loope et al., 1998; Dashzeveg 40:133–266. CHIAPPE, L., J. G. SCHMIDT, F. D. JACKSON, A. GARRIDO, L. DINGUS, et al., 2005). However, the presence of well-developed foresets AND G. GRELLET-TINNER. 2004. Nest structure for sauropods: adjacent to all the fossils preserved at Tugrikin shire, the sedimentary criteria for recognition of dinosaur nesting traces. Palaios, absence of structureless sandy lithofacies there, as well as the 19:89–95. absence of positive evidence for alluvial fan deposits do not CHURE, D., C. TURNER, AND F. PETERSON. 1994. An embryo of support rainstorm-induced grain flows on stablized alluvial Camptosaurus from the Morrison Formation (Jurassic, middle Titho- nian) in Dinosaur National Monument, Utah, p. 298–311. In K. fans as the proximate cause of the deaths at Tugrikin Shire Carpenter, K. F. Hirsch, and J. R. Horner, (eds.), Dinosaur Eggs and generally, or this mortality event in particular (Jerzykiewicz Babies, Cambridge University Press, Cambridge. et al., 1993; Fastovsky et al., 1997). DASHZEVEG, D., L. DINGUS, D. B. LOOPE, C. C. SWISHER III, T. DULAM, Regardless of which of these two modes dominated in each AND M. R. SWEENEY. 2005. New stratigraphic subdivision, depositional of these cases, these juvenile dinosaurs lie in situ and all environment, and age estimate for the Upper Cretaceous Djadokhta Formation, southern Ulan Nur Basin, Mongolia. American Museum of evidence indicates that the inhabitants of the nest were rapidly Natural History Novitates, 3498:1–31. overwhelmed and entombed while still alive. This then DINGUS, L., D. B. LOOPE, C. C. SWISHER III, C. MINJIN, M. J. NOVACEK, reinforces the conclusion that Protoceratops was not simply AND M. A. NORELL. 2008. The geology of Ukhaa Tolgod (Djadokhta passing through the Djadochta dune fields of Tugrikin Shire Formation, Upper Cretaceous, Nemegt Basin, Mongolia). American Museum of Natural History Novitates, 3616:1–40. but rather made its home among the large-scale, sandy, eolian DODSON, P. 1976. Quantitative aspects of relative growth and sexual dunes (Fastovsky et al., 1997). dimorphism in Protoceratops. Journal of Paleontology, 50:929–940. DODSON, P. 1996. The Horned Dinosaurs. Princeton University Press, CONCLUSIONS Princeton, 346 p. Since the discoveries in the early part of the twentieth century DODSON, P., C. A. FORSTER, AND S. D. SAMPSON. 2004. Ceratopsidae, by the expeditions of the American Museum of Natural History p. 494–513. In D. B. Weishampel, P. Dodson, H. Olsmolska, (eds.), The Dinosauria. Univ. of California Press, Berkeley. (Andrews, 1932, 1933), the Gobi Desert of Mongolia and China DONG, Z.-M. AND P. J. CURRIE. 1993. Protoceratopsian embryos from has continued to provide a source of extraordinary dinosaur Inner Mongolia. Canadian Journal of Earth Science, 30:2248–2254. fossils and insights about dinosaurs in the Upper Cretaceous of EBERTH, D. A. 1993. Depositional environments and facies transitions of central Asia. Aside from being among the most spectacular of dinosaur-bearing Upper Cretaceous redbeds at Bayan Mandahu (Inner fossils from a locality known for spectacular fossils (Olsmo´lska, Monglia, People’s Republic of China). Canadian Journal of Earth Science, 30:2196–2213. 1993; Unwin et al., 1995), the inferred Protoceratops nest ERICKSON, G. M., P. J. MAKOVICKY, B. D. INOUYE, C.-F. ZHOU, AND described here strongly supports the inference that some kind of K.-Q. GAO. 2009. A life table for Psittacosaurus lujiatunensis: Initial nest care was involved in the early post-natal developmental insights into ornithischian dinosaur population biology. Anatomical stages of these dinosaurs; however, this cannot be directly Record, 292:1514–1521. demonstrated. MPC-D 100/530 represents an in-situ record of FASTOVSKY, D. E., D. BADAMGARAV, H. ISHIMOTO, M. WATABE, AND D. B. WEISHAMPEL. 1997. The paleoenvironments of Tugrikin-shireh Protoceratops nesting in sandy aeolian dune fields, reinforcing (Gobi Desert, Monglia) and aspects of the taphonomy and paleoecol- the conclusion that it truly lived there. Finally, the animals’ nest ogy of Protoceratops (Dinosauria: Ornithischia). Palaios, 12:59–70. was overrun by sand, likely during a storm, dramatically GAO, K. AND M. A. NORELL. 2000. Taxonomic composition and recording their last living minutes on Earth. systematics of Late Cretaceous lizard assemblages from Ukhaa Tolgod and adjacent localities, Mongolian Gobi Desert. American Museum ACKNOWLEDGMENTS Natural History Bulletin, 249:1–118. GRANGER, W. AND W. K. GREGORY. 1923. Protoceratops andrewsi, a The late Mr. Lkhagvasuren and Mr. Bayardorj are preceratopsian dinosaur from Mongolia. American Museum of Natural gratefully acknowledged for early and final preparation, History Novitates, 72:1–9. Journal of Paleontology pleo-85-06-02.3d 17/8/11 08:47:55 1040 Cust # 11-008R  FASTOVSKY ET AL.—PROTOCERATOPS NEST 1041 HORNER, J. R. 1984. The nesting behavior of dinosaurs. Scientific MENG, Q., J. LIU, D. J. VARRICCHIO, T. HUANG, AND C. GAO. 2004. American, 250:130–137. Parental care in an ornithischian dinosaur. Nature, 431:145–146. HORNER, J. R. AND R. MAKELA. 1979. Nest of juveniles provides evidence OSMO´LSKA, H. 1993. Were the Mongolian ‘‘fighting dinosaurs’’ really of family structure among dinosaurs. Nature, 282:296–298. fighting? Rev. Pale´obiol. vol. spe´c., 7:161–162. HORNER, J. R. AND D. B. WEISHAMPEL. 1988. A comparative SANEYOSHI, M. AND M. WATABE. 2007. Paleo-wind direction of the embryological study of two ornithischian dinosaurs. Nature, 332:256– Upper Cretaceous Djadokhta Formation in central part of the Gobi 257. desert, Mongolia. Journal of the Geological Society of Japan, 113:V–VI. HORNER, J. R. 2000. Dinosaur reproduction and parenting. Annual SERENO, P. C. 1986. Phylogeny of the bird-hipped dinosaurs (Order Reviews of Earth and Planetary Sciences, 28:19–45. Ornisthischia). National Geographic Research, 2:234–256. HORNER, J. R., K. PADIAN, AND A. DERICQLE`S. 2001. Comparative SERENO, P. C. 2000. The fossil record, systematics, and evolution of of osteo-histology of some embryonic and perinatal archosaurs: phyloge- pachycephalosaurs and ceratopsians from Asia, p. 480–516. In M. J. netic and behavioral implications for dinosaurs. Paleobiology, 27:39–58. Benton, M. A. Shishkin, D. M. Unwin, and E. N. Kurochkin (eds.), The ISHII, K., M. WATABE, S. SUZUKI, S. ISHIGAKI, R. BARSBOLD, AND KH. Age of Dinosaurs in Russia and Mongolia. Cambridge University Press, TSOGTBAATAR (eds.). 2000. Results of Hayashibara Museum of Natural Cambridge, U.K. Sciences and Mongolian Academy of Sciences and Mongolian THULBORN, A. 1992. Nest of the dinosaur Protoceratops. Lethaia, 25:145– Paleontological Center Joint Paleontological Expedition. Hayashibara 149. Museum of Natural Sciences Research Bulletin, 1:1–137. JERZYKIEWICZ, T., P. J. CURRIE, D. A. EBERTH, P. S. JOHNSTON, E. H. TURNER, A. H., D. POL, J. A. CLARKE, G. M. ERICKSON, AND M. A. KOSTER, AND J.-J. ZHENG. 1993. Djadokhta Formation correlative NORELL. 2007. A basal dromaeosaurid and size evolution preceding strata in Chinese Inner Mongolia: an overview of the stratigraphy, avian flight. Science, 317:1378–1381. sedimentary geology, and paleontology and comparisons with the type UNWIN, D. M., A. PERLE, AND C. TRUEMAN. 1995. Protoceratops and locality in the pre-Altai Gobi. Canadian Journal of Earth Science, Velociraptor preserved in association: evidence for predatory behavior 30:2180–2190. in dromaeosaurid dinosaurs. Journal of Vertebrate Paleontology, LAMBERT, O., P. GODEFROIT, H. LI, C.-Y. SHANG, AND Z.-M. DONG. 15(Suppl. to 3):57A–58A. 2001. A new species of Protoceratops (Dinosauria, Neoceratopsia) from WEISHAMPEL, D. B. AND J. R. HORNER. 1986. The hadrosaurid dinosaurs the Late Cretaceous of Inner Mongolia (P. R. China). Bull. Inst. Roy. from the Iren Dabasu fauna (People’s Repubic of China, Late Sci. Nat. Belg. Sci. Terre, 71:5–28. Cretaceous). Journal of Vertebrate Paleontology, 6:38–45. LONG, J. A. AND K. J. MCNAMARA. 1995. Heterochrony in dinosaur WEISHAMPEL, D. B., D. E. FASTOVSKY, M. WATABE, R. BARSBOLD, AND evolution, p. 151–168. In K. J. McNamara, (ed), Evolutionary Change KH. TSOGTBAATAR. 2000. New embryonic and hatchling dinosaur and Heterochrony. Wiley, London. remains from the Late Cretaceous of Mongolia. Journal of Vertebrate LOOPE, D. A., L. DINGUS, C. C. SWISHER III, AND C. MINJIN. 1998. Life Paleontology, 20(suppl. to 3):78A. and death in a Late Cretaceous dune field, Nemegt basin, Mongolia. YOU, H. AND P. DODSON. 2004. Basal Ceratopsia, p. 478–493. In D. B. Geology, 26:27–30. Weishampel, P. Dodson, and H. Olsmolska, (eds.), The Dinosauria. MAKOVICKY, P. J., R. SADLER, P. DODSON, G. M. ERICKSON, AND M. A. Univ. of California Press, Berkeley. NORELL. 2007. Life history of Protoceratops andrewsi from Bayn Zag, ZHAO, Q., P. BARRETT, AND D. A. EBERTH. 2007. Social behaviour and Mongolia. Journal of Vertebrate Paleontology, 27:109A. mass mortality in the basal ceratopsian dinosaur Psittacosaurus (Early MARSH, O. C. 1890. Additional characters of the Ceratopsidae, with Cretaceous, People’s Republic of China). Palaeontology, 50:1023–1029. notice of new Cretaceous dinosaurs. American Journal of Science, Series 3, 39:418–426. ACCEPTED 16 MAY 2011 Journal of Paleontology pleo-85-06-02.3d 17/8/11 08:47:56 1041 Cust # 11-008R