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The opisthotonic posture of vertebrate skeletons: postmortem contraction or death throes?

Published online by Cambridge University Press:  14 July 2015

Cynthia Marshall Faux  and
Kevin Padian
Cynthia Marshall Faux
Affiliation:
Department of Paleontology, Museum of the Rockies, Bozeman, Montana 59718 Division of Vertebrate Paleontology, Yale Peabody Museum, New Haven, Connecticut 06520. E-mail: [email protected]
Kevin Padian
Affiliation:
Department of Integrative Biology and Museum of Paleontology, University of California, Berkeley, California 94720. E-mail: [email protected]
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Abstract

An extreme, dorsally hyperextended posture of the spine (opisthotonus), characterized by the skull and neck recurved over the back, and with strong extension of the tail, is observed in many well-preserved, articulated amniote skeletons (birds and other dinosaurs, pterosaurs, and at least placental mammals). Postmortem water transport may explain some cases of spinal curvature in fossil tetrapods, but we show how these can be distinguished from causes of the opisthotonic posture, which is a biotic syndrome. Traditional biotic explanations nearly all involve postmortem causes, and have included rigor mortis, desiccation, and contraction of tendons and ligaments. However, examination of the process of rigor mortis and experimental observations of drying and salinity in carcasses of extant animals show that these explanations of the “dead bird” (opisthotonic) posture account for few or no cases. Differential contraction of cervical ligaments after death also does not produce the opisthotonic posture. It is not postmortem contraction but perimortem muscle spasms resulting from various afflictions of the central nervous system that cause these extreme postures. That is, the opisthotonic posture is the result of “death throes,” not postmortem processes, and individuals so afflicted assumed the posture before death, not afterward. The clinical literature has long recognized that such afflicted individuals perish from asphyxiation, lack of nourishment or essential nutrients, environmental toxins, or viral infections, among other causes. Accepting the actual causes of the opisthotonic posture as perimortem and not postmortem provides insights into the causes of death of fossilized specimens, and also revises interpretations of paleoenvironmental conditions of many fossil deposits. The opisthotonic posture tells us more about the circumstances surrounding death than about what happened after death. Finally, the opisthotonic posture appears to have a phylogenetic signal: it is so far reported entirely in ornithodiran archosaurs (dinosaurs and pterosaurs) and in crown-group placentals, though the distribution in mammals may expand with further study. It seems important that the opisthotonic posture has been observed extensively only in clades of animals that are known or thought to have high basal metabolic rates: hypoxia and related diseases would be most likely to affect animals with high oxygen use rates.

Type
Articles
Information
Paleobiology , Volume 33 , Issue 2 , Spring 2007 , pp. 201 - 226
Copyright
Copyright © The Paleontological Society 

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References

Literature Cited

Kappers, C. U. Ariens, Huber, G. C., and Crosby, E. C. 1960. The comparative anatomy of the nervous system of vertebrates, including man. Hafner, New York.Google Scholar
Austin, R. J., Whiting, T. L., Anderson, R. A., and Drebot, M. A. 2004. An outbreak of West Nile virus-associated disease in domestic geese (Anser anser domesticus) upon initial introduction to a geographic region, with evidence of bird to bird transmission. Canadian Veterinary Journal 45:117–123.Google Scholar
Bagley, R. S. 2005. Fundamentals of clinical neurology. Blackwell, Ames, Iowa. Google Scholar
Barthel, K. W. 1970. On the deposition of the Solnhofen limestone (Lower Tithonian, Bavaria, Germany). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 135:1–18.Google Scholar
Barthel, K. W., Swinburne, N. H. M., and Morris, S. Conway 1990. Solnhofen: a study in Mesozoic palaeontology. Cambridge University Press, New York.Google Scholar
Bergman, R. A. 1983. Ultrastructural configuration of sarcomeres in passive and contracted frog sartorius muscle. American Journal of Anatomy 166:209–222.Google Scholar
Bickart, K. J. 1984. A field experiment in avian taphonomy. Journal of Vertebrate Paleontology 4:525–535.CrossRefGoogle Scholar
Bonaparte, J. F., and Vince, M. 1979. El hallazgo del primer nido de dinosaurios triásicos (Saurischia, Prosauropoda), Triásico Superior de Patagonia, Argentina. Ameghiniana 16:173–182.Google Scholar
Braun, A., and Pfeiffer, T. 2002. Cyanobacterial blooms as the cause of a Pleistocene large mammal assemblage. Paleobiology 28:139–154.2.0.CO;2>CrossRefGoogle Scholar
Brinkman, D. L., Cifelli, R. L., and Czaplewski, N. J. 1998. First occurrence of Deinonychus antirrhopus (Dinosauria: Theropoda) from the Antlers Formation (Lower Cretaceous: Aptian-Albian) of Oklahoma. Oklahoma Geological Survey Bulletin 146:1–27.Google Scholar
Buckland, W. 1824. Reliquae diluvianae, 2d ed. London. [Extract in Philosophical Transactions of the Royal Society of London 112:171–236, Plates 15–26 (1822).] Google Scholar
Camp, C. L., and Smith, N. 1942. Phylogeny and functions of the digital ligaments of the horse. University of California Memoirs 13:69–124.Google Scholar
Chaffee, R. G. 1952. The Deseadan vertebrate fauna of the Scarritt Pocket, Patagonia. Bulletin of the American Museum of Natural History 98:503–562.Google Scholar
Chang, M.-M., ed. 2003. The Jehol Biota: the emergence of feathered dinosaurs, beaked birds and flowering plants. Shanghai Scientific and Technical Publishers, Shanghai.Google Scholar
Channing, A., Schweitzer, M. H., Horner, J. R., and McEneaney, T. 2005. A silicified bird from Quaternary hot spring deposits. Proceedings of the Royal Society of London B 272:905–911.Google Scholar
Constantini, S., and Beni, L. 1993. Reversible opisthotonus following intracranial pressure changes in Chiari malformation. Child's Nervous System 6:350–352.Google Scholar
Cossu, G., Melis, M., Melis, G., Maccioni, E., Putzu, V., Catte, O., and Putzu, P. 2004. Reversible Pisa syndrome (pleurothotonus) due to the cholinesterase inhibitor galantamine: case report. Movement Disorders 19:1243–1244.Google Scholar
Curry, K. A. 1999. Ontogenetic histology of Apatosaurus (Dinosauria: Sauropoda): new insights on growth rates and longevity. Journal of Vertebrate Paleontology 19:654–665.Google Scholar
Dalian Natural History Museum. 2005. Jehol biota. CD format. http://www.dlnm.org. 40 Xicun Street, Heijhijiao, Shahekou District, Dalian, China 116023.Google Scholar
Dart, R. 1925. Australopithecus africanus: the man-ape of South Africa. Nature 115:195–199.Google Scholar
Davis, P., Macefield, G., and Nail, B. S. 1986. Respiratory muscle activity during asphyxic apnoea and opisthotonus in the rabbit. Respiratory Physiology 65:285–294.Google Scholar
Davis, P. G. 1996. The taphonomy of Archaeopteryx . Bulletin of the National Science Museum 22C:91–106.Google Scholar
Davis, P. G., and Briggs, D. E. G. 1998. Impact of decay and disarticulation on the preservation of fossil birds. Palaios 13:3–13.Google Scholar
de Buisonjé, P. H. 1985. Climatological conditions during deposition of the Solnhofen limestones. Pp. 45–65 in Hecht, M. K., Ostrom, J. H., Viohl, G., and Wellnhofer, P., eds. The beginnings of birds: proceedings of the International Archaeopteryx Conference, 1984. Freunde des Jura-Museums, Eichstätt.Google Scholar
Deecke, W. 1915. Paläontologische Betrachtungen. VII. Über crustaceen. Neues Jahrbuch für Mineralogie, Geologie, und Paläontologie 1:112–126.Google Scholar
de Lahunta, A. 1983. Veterinary neuroanatomy and clinical neurology. W. B. Saunders, Philadelphia.Google Scholar
Ersahin, Y., Mutluer, S., and Guzelbag, E. 1992. A case of double-compartment hydrocephalus presenting with opisthotonus. Surgical Neurology 38:291–293.Google Scholar
Filippich, L., and Cao, G. 1993. Experimental acute yellow-wood (Terminalia oblongata) intoxication in sheep. Australian Veterinary Journal 70:214–218.Google Scholar
Frey, E., and Martill, D. M. 1994. A new pterosaur from the Crato Formation (Lower Cretaceous, Aptian) of Brazil. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 194:379–412.Google Scholar
Gellman, K. S., Bertram, J. E. A., and Hermanson, J. W. 2002. Morphology, histochemistry, and function of epaxial cervical musculature in the horse (Equus caballus). Journal of Morphology 251:182–194.CrossRefGoogle ScholarPubMed
Gillette, D. D. 1994. Seismosaurus: the earth shaker. Columbia University Press, New York.Google Scholar
Gilmore, C. W. 1925. A nearly complete articulated skeleton of Camarasaurus, a saurischian dinosaur from the Dinosaur National Monument, Utah. Memoirs of the Carnegie Museum 10:347–384, Plates xiii-xvii.Google Scholar
Grande, L., 1984. Paleontology of the Green River Formation, with a review of the fish fauna. Geological Survey of Wyoming Laramie.Google Scholar
Greene, W. F., and Laurens, H. 1923. The effect of extirpation on the embryonic ear and eye on equilibrium in Amblystoma . American Journal of Physiology 64:120–143.Google Scholar
Hanna, R. R. 2002. Multiple injury and infection in a sub-adult theropod dinosaur Allosaurus fragilis with comparisons to allosaur pathology in the Cleveland-Lloyd dinosaur quarry collection. Journal of Vertebrate Paleontology 22:76–90.Google Scholar
Hauff, B. 1960. Das Holzmadenbuch. Hohenlohe'schen Buchhandlung, Oehringen, Germany. Google Scholar
Heinroth, O. 1923. Die Flugel von Archaeopteryx . Journal für Ornithologie 71:277–283.CrossRefGoogle Scholar
Henssge, C., Knight, B., Krompecher, T., Madea, B., and Nokes, L. 1995. The estimation of the time since death in the early postmortem period. Arnold, London.Google Scholar
Hill, A. 1979. Disarticulation and scattering of mammal skeletons. Paleobiology 5:261–274.Google Scholar
Hill, A., and Behrensmeyer, A. K. 1984. Disarticulation patterns of some modern East African mammals. Paleobiology 10:366–376.Google Scholar
Holland, C. T., Charles, J. A., Smith, S. H., and Cortaville, P. E. 2000. Hemihyperaesthesia and hyperresponsiveness resembling central pain syndrome in a dog with a forebrain oligodendroglioma. Australian Veterinary Journal 78:676–680.Google Scholar
Holliday, T. A. 1980. Clinical signs of acute and chronic experimental lesions of the cerebellum. Veterinary Science Communications 3:259–278.Google Scholar
Hullard, T. J. 1985. Muscles and tendons. Pp. 139–199 in Jubb, K. V. F., Kennedy, P. C., and Palmer, N., eds. Pathology of domestic animals. Academic Press, Orlando.Google Scholar
Ji, Q., Currie, P. J., Ji, S., and Norell, M. GA. 1998. Two feathered dinosaurs from northeastern China. Nature 393:753–761.Google Scholar
Klein, D., Novilla, M., and Watkins, K. 1994. Nutritional encephalomalacia in turkeys: diagnosis and growth performance. Avian Diseases 38:653–659.Google Scholar
Kobayashi, M., Takatori, T., Iwadate, K., and Nakajima, M. 1996. Reconstruction of the sequence of rigor mortis through postmortem changes in adenosine nucleotides and lactic acid in different rat muscles. Forensic Science International 82:243–253.Google Scholar
Koenigswald, W. von, Braun, A., and Pfeiffer, T. 2004. Cyanobacteria and seasonal death: a new taphonomic model for the Eocene Messel lake. Paläontologische Zeitschrift 78:417–424.Google Scholar
Krauss, D., Petrucelli, D., and Lincoln, T. 2005. Results of an experiment in avian taphonomic processes reveal a mechanism for the sub-aqueous deposition of bird remains. Journal of Vertebrate Paleontology 25(Suppl. to No. 3):79A–80A.Google Scholar
Krompecher, T. 1981. Experimental evaluation of rigor mortis. V. Effect of various temperatures on the evolution of rigor mortis. Forensic Science International 17:19–26.Google Scholar
Krompecher, T. 1994. Experimental evaluation of rigor mortis. VIII. Estimation of time since death by repeated measurements of the intensity of rigor mortis on rats. Forensic Science International 68:149–159.Google Scholar
Krompecher, T. 1995. Rigor mortis: estimation of the time since death by evaluation of the cadaveric rigidity. Pp. 148–167 in Knight, B., ed. The estimation of time since death in the early post-mortem period. Arnold, London.Google Scholar
Krompecher, T., and Fryc, O. 1978. Experimental evaluation of rigor mortis. IV. Change in strength and evolution of rigor mortis in the case of physical exercise preceding death. Forensic Science International 12:103–107.Google Scholar
Krompecher, T., Bergerioux, C., Brandt-Casadevall, C., and Gujer, H.-R. 1983. Experimental evaluation of rigor mortis. VI. Effect of various causes of death on the evolution of rigor mortis. Forensic Science International 22:1–9.Google Scholar
Laws, R. R. 1996. Paleopathological analysis of a sub-adult Allosaurus fragilis (MOR 693) from the Upper Jurassic Morrison Formation with multiple injuries and infections. . Montana State University, Bozeman.Google Scholar
Liu, J., Xiao, H., Lei, F., Zhu, Q., Qin, K., Zhang, X.-w., Zhang, X.-l., Zhao, D., Wang, G., Feng, Y., Ma, J., Liu, W., Wang, J., and Gao, G. F. 2005. Highly pathogenic H5N1 influenza virus infection in migratory birds. Science 309:1206.Google Scholar
Loomis, F. M. 1910. Osteology and affinities of the genus Stenomylus . American Journal of Science 29:297–321.Google Scholar
Lorenz, M. D., and Kornegay, J. N. 2004. Handbook of veterinary neurology. Saunders, St. Louis.Google Scholar
Lortet, L. 1892. Les reptiles du Bassin du Rhône. Archives du Muséum d'Histoire Naturelle de Lyon 5:3–139, Plates I–XII.Google Scholar
Miller, A., and Tregear, R. T. 1972. Structure of insect fibrillar flight muscle in the presence and absence of ATP. Journal of Molecular Biology 70:85–104.Google Scholar
Moodie, R. L. 1918. Studies in paleopathology. III. Opisthotonus and allied phenomena among fossil vertebrates. American Naturalist 52:384–394.Google Scholar
Moodie, R. L. 1923. Paleopathology: an introduction to the study of ancient evidences of disease. University of Illinois Press, Urbana.CrossRefGoogle Scholar
Nagy, K. A. 1987. Field metabolic rates and food requirement scaling in mammals and birds. Ecological Monographs 57:111–128.Google Scholar
Olby, N., Blot, S., Thibaud, J.-L., Phillips, J., O'Brien, D. P., Burr, J., Berg, J., Brown, T., and Breen, M. 2004. Cerebellar cortical degeneration in adult American Staffordshire terriers. Journal of Veterinary Internal Medicine 18:201–208.Google Scholar
Ondo, W. G., and Delong, G. R. 1996. Dandy-Walker syndrome presenting as opisthotonus: proposed pathophysiology. Pediatric Neurology 14:165–168.Google Scholar
O'Reilly, S., O'Hearn, E., Struck, R. F., Rowinsky, E. K., and Molliver, M. E. 2003. The alkylating agent penclomedine induces degeneration of purkinje cells in the rat cerebellum. Investigational New Drugs 23:269–279.Google Scholar
Ostrom, J. H. 1978. The osteology of Compsognathus longipes Wagner. Zitteliana 4:73–118.Google Scholar
Padian, K., and Horner, J. R. 2004. Dinosaur physiology. Pp. 660–671 in Weishampel, D., Dodson, P., and Osmolska, H., eds. The Dinosauria, 2d ed. University of California Press, Berkeley.Google Scholar
Padian, K., de Ricqlès, A. J., and Horner, J. R. 2001. Dinosaurian growth rates and bird origins. Nature 412:405–408.Google Scholar
Palmer, M. V. 2002. Atlantoaxial instability in a white-tailed deer fawn (Odocoileus virginianus). Journal of Wildlife Diseases 38:860–862.Google Scholar
Palmqvist, P., and Arribas, A. 2001. Taphonomic decoding of the paleobiological information locked in a lower Pleistocene assemblage of large mammals. Paleobiology 27:512–530.Google Scholar
Park, S. Y., Glaser, C., Murray, W. J., Kazacos, K. R., Rowley, H. A., Fredrick, D. R., and Bass, N. 2000. Raccoon roundworm (Baylisascaris procyonis) encephalitis: case report and field investigation. Pediatrics 100:e56.CrossRefGoogle Scholar
Peterson, O. A. 1911. A mounted skeleton of Stenomylus hitchcocki, the Stenomylus Quarry, and remarks upon the affinities of the genus. Annals of the Carnegie Museum 7:267–273, with plates.Google Scholar
Peyer, K. 2004. A re-evaluation of the French Compsognathus of the Tithonian of southeastern France and its phylogenetic relationships with other compsognathids and coelurosaurs in general. Ph.D. dissertation. National Museum of Natural History, Paris.Google Scholar
Philbey, A., and Martel, K. 2003. A multifocal symmetrical necrotising encephalomyelopathy in Angus calves. Australian Veterinary Journal 81:226–229.Google Scholar
Pi, L., Ou, Y., and Ye, Y. 1996. A new species of sauropod from Zigong, Sichuan, Mamenchisaurus youngi . Papers on geosciences contributed to the 30th International Geological Congress, pp. 87–91. [Translated by Will Downs; available from Polyglot Paleontology.] Google Scholar
Provenzano, P. P., and Vanderby, R. Jr. 2006. Collagen fibril morphology and organization: implications for force transmission in ligament and tendon. Matrix Biology 25:71–84.Google Scholar
Real, F., Fernandez, A., Acosta, F., Acosta, B., Castro, P., Deniz, S., and Oros, J. 1997. Septicemia associated with Hafnia alvei in laying hens. Avian Diseases 41:741–747.Google Scholar
de Ricqlès, A. J. 1980. Tissue structures of dinosaur bone: functional significance and possible relation to dinosaur physiology. In Thomas, R. D. K. and Olson, E. C., eds. A cold look at the warm-blooded dinosaurs. AAAS Selected Symposium 28:103–139. Westview Press, Boulder, Colo. Google Scholar
Ricqlès, A. J. de, Padian, K., Horner, J. R., and Francillon-Vieillot, H. 2000. Palaeohistology of the bones of pterosaurs (Reptilia: Archosauria): anatomy, ontogeny, and biomechanical implications. Zoological Journal of the Linnean Society 129:349–385.Google Scholar
Rothschild, B. M., and Martin, L. D. 1993. Paleopathology: disease in the fossil record. CRC Press, Ann Arbor.Google Scholar
Ryan, M. J., Russell, A. P., Eberth, D. A., and Currie, P. J. 2001. The taphonomy of a Centrosaurus (Ornithischia: Ceratopsidae) bone bed from the Dinosaur Park Formation (Upper Campanian), Alberta, Canada, with comments on cranial ontogeny. Palaios 16:482–506.Google Scholar
Sander, P. M. 2000. Longbone histology of the Tendaguru sauropods: implications for growth and biology. Paleobiology. 26:466–488.Google Scholar
Saunders, P. R. I., and Harris, M. N. E. 1990. Opisthotonus and other unusual neurological sequelae after outpatient anaesthesia. Anaesthesia 45:552–557.Google Scholar
Schaal, S., and Ziegler, W., eds. 1988. Messel: Ein Schaufenster in die Geschichte der Erde und des Lebens. Kramer, Frankfurt am Main, Germany. Google Scholar
Schäfer, W. 1962. Aktuo-Paläontologie nach Studien in der Nordsee. Waldemar Kramer, Frankfurt.Google Scholar
Schäfer, W. 1972. Ecology and paleoecology of marine environments. University of Chicago Press, Chicago.Google Scholar
Schweitzer, M. H., and Marshall, C. L. 2001. A molecular model for the evolution of endothermy in the theropod-bird lineage. Journal of Experimental Zoology (Molecular and Developmental Evolution) 291:317–338.Google Scholar
Seilacher, A., Reif, W.-E., and Westphal, F. 1985. Sedimentological, ecological and temporal patterns of fossil Lagerstätten. Philosophical Transactions of the Royal Society of London B 311:5–23.Google Scholar
Skjervold, P. O., R⊘rå, A. M. B., Fjæra, S. O., Vegusdal, A., Vorre, A., and Einen, O. 2001. Effects of pre-, in-, or post-rigor filleting of live chilled Atlantic salmon. Aquaculture 194:315–326.Google Scholar
Sledzik, P. S. 1990. Forensic taphonomy: postmortem decomposition and decay. Pp. 109–119 in Grupe, G. and Garland, A. N., eds. Histology of ancient human bone: methods and diagnosis. Springer, Berlin.Google Scholar
Stedman, T. L. 1982. Stedman's medical dictionary. Williams and Wilkins, Baltimore.Google Scholar
Sukoff, M. H., and Ragatz, R. E. 1980. Cerebellar stimulation for chronic extensor-flexor rigidity and opisthotonus secondary to hypoxia: report of two cases. Journal of Neurosurgery 53:391–396.Google Scholar
Sullivan, T. 1970. Thiamine deficiency presenting as opisthotonus. Journal of Pediatrics 77:1092–1102.Google Scholar
Swank, R. L. 1940. Avian thiamine deficiency: a correlation of the pathology and clinical behavior. Journal of Experimental Medicine 71:683–709.Google Scholar
Uzal, F. A., Kelly, W. R., Morris, W. E., Bermudez, J., and Baison, M. 2004. The pathology of peracute experimental Clostridium perfringens type D enterotoxemia in sheep. Journal of Veterinary Diagnostic Investigation 16:403–411.Google Scholar
Van der Lugt, J., Markus, M., Kitching, J., and Daly, T. 1994. Necrotic encephalitis as a manifestation of acute sarcocystosis in cattle. Journal of the South African Veterinary Association 65:119–121.Google ScholarPubMed
Viohl, G. 1985. Geology of the Solnhofen lithographic limestone and the habit of Archaeopteryx . Pp. 31–44 in Hecht, M. K., Ostrom, J. H., Viohl, G., and Wellnhofer, P., eds. The beginnings of birds: proceedings of the International Archaeopteryx Conference, 1984. Freunde des Jura-Museums, Eichstatt.Google Scholar
Viohl, G. 1994. Fish taphonomy of the Solnhofen Plattenkalk—an approach to the reconstruction of the palaeoenvironment. Geobios 16:81–90.Google Scholar
Weigelt, J. 1927 (1989). Rezente Wirbeltierleichen und ihre paläobiologische Bedeutung (Recent vertebrate carcasses and their paleobiological implications). University of Chicago Press, Chicago.Google Scholar
Welles, S. P. 1943. Elasmosaurid plesiosaurs with description of new material from California and Colorado. Memoirs of the University of California 13:125–254.Google Scholar
Wellnhofer, P. 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlung der Bayerischen Akademie der Wissenschaften, Neue Folge, 141:1–133.Google Scholar
Wellnhofer, P. 1971. Die Atoposauridae (Crocodylia, Mesosuchia) der Oberjura-Plattenkalke Bayerns. Paläontographica A 138:133–165.Google Scholar
Wellnhofer, P. 1975. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Teil I. Allgemeine Skelletmorphologie. Paläontographica A 148:1–33, 11 plates. Teil II. Systematische beschreibung. Paläontographica A 148:132–186. Teil III. Palökologie und Stammesgeschichte. Paläontographica A 149:1–30, 13 plates.Google Scholar
Wellnhofer, P. 1991. The illustrated encyclopedia of pterosaurs. Salamander, London.Google Scholar
Wyatt, R. D., Simmons, D. G., and Hamilton, P. B. 1975. Induced systemic candidiasis in young broiler chickens. Avian Diseases 19:533–543.Google Scholar
Xu, X., and Norell, M. A. 2004. A new troodontid dinosaur from China with avian-like sleeping posture. Nature 431:838–841.Google Scholar
Xu, X., Wang, X.-L., and You, H.-L. 2000. A primitive ornithopod from the Early Cretaceous Yixian Formation of Liaoning. Vertebrata Palasiatica 38:318–325.Google Scholar
Young, C. C. 1958. The dinosaurian remains of Laiyang, Shantung. Palaeontologia Sinica C 16:1–138.Google Scholar
Zhou, Z., Barrett, P. M., and Hilton, J. 2003. An exceptionally preserved Lower Cretaceous ecosystem. Nature 421:807–814.Google Scholar