Elsevier

Annales de Paléontologie

Volume 95, Issue 3, July–September 2009, Pages 165-175
Annales de Paléontologie

Original article
Palaeoneuroanatomy of BrachiosaurusPaléoneuroanatomie de Brachiosaurus

https://doi.org/10.1016/j.annpal.2009.06.001Get rights and content

Abstract

An overview of the palaeoneuroanatomy (brain and spinal cord) of the sauropod dinosaur Brachiosaurus is given. Although having a flexed brain configuration, Brachiosaurus presents on the whole a rather moderately derived neuroanatomical pattern. As other sauropods, Brachiosaurus shows an enlargement of the spinal cord in the sacral area. New Encephalization Quotients are calculated and found to be about 0.62 or 0.79 (depending on the body volume taken into consideration) when Hurlburt's formula is used. This suggests that Brachiosaurus, although it may not have been as a low encephalized taxon (by reptilian standards) as previously believed, did have an undersized relative brain volume.

Résumé

Un aperçu général de la paléoneuroanatomie (encéphale et moelle épinière) du dinosaure sauropode Brachiosaurus est donné. En dépit de sa configuration encéphalique contractée, Brachiosaurus présente globalement un patron neuroanatomique modérément dérivé. Comme d’autres sauropodes, Brachiosaurus montre un grossissement de la moelle épinière dans la zone sacrée. De nouveaux Coefficients d’Encéphalisation sont calculés : ils se rapprochent de 0,62 ou 0,79 (selon le volume corporel considéré) quand la formule d’Hurlburt est employée. Ces valeurs suggèrent que Brachiosaurus, bien qu’il ne fût probablement pas aussi peu encéphalisé (pour un reptile) qu’on l’a d’abord cru, avait bel et bien un volume encéphalique relatif « sous-dimensionné ».

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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