Cranial Endocast of the Lambeosaurine Hadrosaurid Amurosaurus riabinini from the Amur Region, Russia Pascaline Lauters1,2*, Martine Vercauteren2, Yuri L. Bolotsky3, Pascal Godefroit1 1 Department of Palaeontology, Royal Belgian Institute of Natural Sciences, Bruxelles, Belgium, 2 Service d’Anthropologie et Ge´ne´tique Humaine, Universite´ Libre de Bruxelles, Bruxelles, Belgium, 3 Geological and Nature Exploration Institute, Far Eastern Branch of the Russian Academy of Sciences, Blagoveschensk, Russia Abstract Information on the structure of the brain of the lambeosaurine hadrosaurid dinosaur Amurosaurus riabinini, from the Late Maastrichtian of Blagoveschensk, Far Eastern Russia, is presented based on endocranial casts. The endocasts are compared with physical and digital endocasts of other dinosaurs. The olfactory tract was large. The cerebral hemispheres are enlarged and round, illustrating the important development of this part of the brain in hadrosaurids. The pituitary body is enlarged as well, perhaps prefiguring the large size attained by hadrosaurids. The EQ of Amurosaurus was similar to that of the lambeosaurine dinosaur Hypacrosaurus altispinus and was relatively larger than in most extant non-avian reptiles, including sauropod and ceratopsian dinosaurs. However, it was apparently relatively smaller than those of most theropod dinosaurs. The relatively large size of the cerebrum is consistent with the range and complexity of social behaviors inferred for lambeosaurine dinosaurs. Citation: Lauters P, Vercauteren M, Bolotsky YL, Godefroit P (2013) Cranial Endocast of the Lambeosaurine Hadrosaurid Amurosaurus riabinini from the Amur Region, Russia. PLoS ONE 8(11): e78899. doi:10.1371/journal.pone.0078899 Editor: Richard J. Butler, University of Birmingham, United Kingdom Received April 9, 2013; Accepted September 16, 2013; Published November 13, 2013 Copyright: ß 2013 Lauters et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study was realized through the execution of S&T bilateral cooperation agreements on behalf of the Belgian State, Federal Scientific Policy. It constitutes part of a Ph.D. thesis by PL at the Universite´ Libre de Bruxelles, thanks to a grant from the Fonds pour la formation a` la Recherche dans l’Industrie et l’Agriculture. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: [email protected] Introduction morphology of the brain [13,14,15,16,17]. Subsequently, we compare the encephalization quotient and the cerebral volume of Since 1902, and the first discovery of dinosaur fossils in the Amurosaurus to those of other dinosaurs. Independently published Amur region (Far Eastern Russia), thousands of bones were data about the endocranial anatomy of this species based upon the collected from this area. Most of them belong to hadrosaurid taxa. same material [18] is also discussed, and interpretations contrasted Amurosaurus riabinini Bolotsky and Kurzanov, 1991 [1,2] and with those presented here. Finally, hypotheses about the behavior Kerberosaurus manakini Bolotsky and Godefroit, 2004 [3] were found of lambeosaurine hadrosaurid dinosaurs are proposed. in Blagoveschensk, whereas Olorotitan arharensis Godefroit, Bolotsky, and Alifanov, 2003 [4] was found in Kundur, both localities being Materials and Methods in the Amur Region of Far Eastern Russia. Charonosaurus jiayinensis Godefroit, Zan, and Jin, 2000 [5,6], Sahaliyania elunchunorum Institutional Abbreviations Godefroit, Shulin, Tinghai, and Lauters, 2008 [7] and Wulaga- AEHM, Amur Natural History Museum, of the Amur Complex saurus dongi Godefroit, Shulin, Tinghai, and Lauters, 2008 [7] were Integrated Research Institute of the Far Eastern Branch of the found in the adjacent region of China (Heilongjiang Province). Russian Academy of Sciences, Blagoveschensk, Russia (Amur Among this material, some braincases of Amurosaurus were KNII FEB RAS); IRSNB, Institut Royal des Sciences Naturelles found. The brain is a structure very sensitive to rapid decay after de Belgique, Brussels, Belgium. the death of the animal and is thus generally lost before any fossilization. Natural endocasts are rare [8,9], and until recently Specimens the endocranial cavity of fossil taxa was generally inaccessible for IRSNB R 279 (endocast of AEHM 1/232), IRSNB R 280 study without destructive preparation ([10]: p. 38). Recently, high- (endocast of AEHM 1/233), and IRSNB R 281 (endocast of resolution x-ray CT scan was often used to access the endocranial AEHM 1/90), and AEHM 1/240. cavity of fossil specimens. However, in some cases this method is impractical; the specimen may be too small or too large to be CT scanned, or researchers cannot access easily the machine or the Ethics Statement cost to use it is too high. It is also possible in some cases to make an This study is based on study of material held in the endocast without damaging the specimen, using materials such as collections of the Amur Natural History Museum. No permits silicone or latex rubber [11,12]. were required for the described study, which complied with all The purpose of this paper is to describe the endocast and the relevant regulations. cranial nerves of Amurosaurus riabinini, and is based on the assumption that the casts provide a good insight into the general PLOS ONE | www.plosone.org 1 November 2013 | Volume 8 | Issue 11 | e78899 Endocast of Amurosaurus riabinini Description ectotherms. Hopson [13] concluded that the EQs of dinosaurs The casts were obtained on the basis of a complete and are usually placed between those of modern ectotherms and undistorted braincase (AEHM 1/232) and partial braincases endotherms. Hurlburt [14] adapted Jerison’s ‘‘lower’’ vertebrate (AEHM 1/90 and AEHM 1/233) of Amurosaurus riabinini. AEHM equation for non-avian-reptiles and defined a Reptile Encephali- 0.553 1/232 and AEHM 1/90 were described in the revision of the zation Quotient (REQ). REQ = MBr/(0.0155*MBd ), where genus by Godefroit et al. [2]. The specimen AEHM 1/233 shows MBr is the mass of the brain (in grams), and MBd is the mass of the the prominent median process between the basipterygoid body (in grams). The mass of the brain is obtained by multiplying processes typical of Amurosaurus riabinini and is referred to this the volume of the brain by 1.036 g/ml [21]. taxon. The presence of valleculae was observed on an additional In extinct taxa, both the brain and body masses must be specimen (AEHM 1/240). The complete braincase (AEHM 1/ estimated, leading to many uncertainties in the calculation of the 232) was used to make the cast IRSNB R 279 and the description REQ. Given that no complete skeleton of Amurosaurus has been of the global features of the endocranial cavity. More details about discovered, it is difficult to estimate the mass of an adult individual, the cranial nerves could be observed on the casts of two partial because no braincase is directly associated to appendicular bones. braincases: IRSNB R 280 and IRSNB R 281. These specimens Because AEHM 1/232 clearly belongs to a large adult specimen, were collected during the 1980s field campaign from the Upper we selected the longest femur and humerus and measured their Cretaceous Udurchukan Formation (Maastrichtian, Late Creta- circumference in order to estimate the mass of a large adult ceous) by Yuri L. Bolotsky. The braincases are fused and from Amurosaurus. The specimens were selected according to their large, presumably adult, individuals. For a complete description of lambeosaurine characteristics [2] and for their size indicating that the braincase of this species, see Godefroit et al. [2]. For general they belonged to an adult individual [22]. In addition, the ratio of measurements of the braincase AEHM 1/232, see Table 1. The humerus/femur circumferences of the selected bones matches the specimens used here were also among those used by Saveliev et al. ratio obtained for articulated adult hadrosaurid skeletons [23,24]. [18] in their independent study of the endocranial anatomy of this REQ calculations for dinosaurs usually estimated the volume of species. However, this study is based on a different set of casts and the brain under the assumption that the brain occupied 50% of the new interpretations about the endocranial anatomy and possible endocranial volume [14,20,25]. According to Evans [17] and behavior of Amurosaurus are presented. Evans et al. [26], the extensive valleculae in hadrosaurids imply that the brain occupied a larger portion of the endocranial cavity The specimens were molded using the following technique. The than in other ornithischians and they calculated the REQ based complete braincase was prepared by covering the smallest on a brain size estimate of 60% endocast volume. Because foramina and fractures with modeling clay, the foramen magnum valleculae can also be observed in Amurosaurus specimens, we here was left free. A thin layer of Vaseline was sprayed into the follow the assumption of Evans et al. [26]. endocranial cavity to prevent excessive adherence of the silicone. Silicone was mixed with a catalyst and poured into the endocranial cavity to create the first endocranial silicone layer. This first layer Results was allowed to dry for at least 24 hours. Once dry, additional Systematic Paleontology silicone was poured at intervals to create a multi-layered cast. This DINOSAURIA Owen, 1842 [27] technique allows the strengthening of the endocranial cast and ORNITHISCHIA Seeley, 1887 [28] prevents its tearing. When the last layer of silicone was completely ORNITHOPODA Marsh, 1881 [29] dry, the endocranial cast was pulled out and the braincase was ANKYLOPOLLEXIA Sereno, 1986 [30] subsequently cleaned. HADROSAURIFORMES Sereno, 1986 [30] The volume of the endocast was measured by placing it, HADROSAUROIDEA Cope, 1869 [31] beforehand filled with tiny glass marbles, in water and measuring HADROSAURIDAE Cope, 1869 [31] water displacement.