Original articlePalaeoneuroanatomy of BrachiosaurusPaléoneuroanatomie de Brachiosaurus
Introduction
The palaeoneuroanatomy of the brain of Brachiosaurus (Fig. 1) was described by W. Janensch and published in two livraisons in a supplement volume of Palaeontographica (Janensch, 1935-1936; but see also Janensch, 1936, Janensch, 1938) dedicated to the results of the 1909–1912 Tendaguru expeditions (see Maier, 2003, for a historical report about them). These studies were based on three braincases: MB.R.2223.1 (formerly HMN t 1), MB.R.2180.22.1-4 (formerly HMN S 66), and M.B.R.2384 (formerly HMN Y 1) (Janensch, 1935-1936: Figs. 2–8, 116–118) and the endocasts MB.R.1918 (from MB.R.2384) and MB.R.1919 (from MB.R.2180.22.1-4) (Janensch, 1935-1936: Pl. 13; Figs. 1 and 2). MB.R.2180.22.1-4 belongs to the type specimen of Brachiosaurus brancai, which comes from a moderately sized individual (formerly labelled as “S I”), whose braincase is complete, but has experienced lateral compression.
The aim of this paper is to offer a synthetic re-description of the palaeoneuroanatomy of Brachiosaurus as well as a new Encephalization Quotient estimate.
Institutional abbreviation: HMN, Museum für Naturkunde der Humboldt-Universität zu Berlin, Germany. MB, Museum für Naturkunde, Berlin, Germany.
Section snippets
Brain neuroanatomy
The cerebral and pontine flexures of the brain of Brachiosaurus are well marked and about 50°, an angle comparable to those of other sauropods such as Diplodocus (see e.g., Hopson, 1979: Fig. 16). The general shape of MB.R.1919 (Fig. 1, Fig. 2[A, B]) is strikingly similar to that of Cetiosaurus (Galton and Knoll, 2006: Fig. 6), suggesting at first sight a conservative evolution of the braincase. In fact, Janensch (1935-1936: p. 252) already noted that the braincase of Cetiosaurus, with its
Spinal anatomy
The spinal anatomy of Brachiosaurus is unsatisfactorily known. Based on the data presented by Janensch (1950), the spinal cord of Brachiosaurus may have been about 140% higher in the sacral region than in the dorsal series. More importantly, between the second and third sacral vertebrae, the neural canal expands into a vast chamber about 20 cm high and 13 cm long (a canal extends from this cavity towards the dorsal face of the sacrum). More caudally, in the region of the third sacral vertebra,
Encephalization
Assuming that Brachiosaurus has a cerebrum/cerebrocast ratio close to 1 as in birds and other dinosaurs (e.g., Evans, 2005), the cerebrum of this taxon can be relatively well assimilated to a sphere having a radius of 2.5 cm (Fig. 4). The cerebrum volume of Brachiosaurus would be in this case about 65 mL.
If Brachiosaurus had the same cerebrum volume/brain volume ratio as Allosaurus (a theropod with a similarly contracted brain) according to Larsson et al. (2000), then the volume of the whole
Conclusion
Although showing a flexed brain configuration, Brachiosaurus presents on the whole a rather moderately derived neuroanatomical pattern with almost no patent differential expansion of any part. As for the dimensional aspect, both the assumed overall brain size and EQ of Brachiosaurus are relatively low, even by reptilian standards (only about 70% the volume expected for a reptile of that size). Because intelligent behaviour requires, inter alia, a relatively large brain able to sort and
Acknowledgements
This work arose in part from a conference by F. Knoll on Paleoneuroanatomía y Dinosaurios held at Cuenca within the framework of the summer courses of the Universidad Nacional de Educacion a Distancia. F. Knoll warmly thanks the directors, J.L. Sanz (Universidad Autónoma de Madrid, Madrid) and F. Ortega (Universidad Nacional de Educacion a Distancia, Madrid), for the invitation to take part in the session. Critical reading by L. Chiappe (Natural History Museum of Los Angeles County, Los
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