Elephant brain: Part I: Gross morphology, functions, comparative anatomy, and evolution
Introduction
Despite the attention of the public to elephants and popularity of these animals, many aspects of elephant biology have been incompletely studied. In particular, detailed studies of the nervous system have been limited, notwithstanding a literature dating from the early 19th century. A recent paper brought to light the paucity of information on elephant brain research and provided a stimulus to publish our findings [22]. In the present investigation, we provide a summary of findings on the gross anatomy of elephant brains.
We studied elephant brains and compared them to other mammalian brains, with the objective to collect data on elephant brain gross morphology. Evolutionary inferences were made based on our examination of ontogenetic stages of elephant brains, from endocasts, and from structures preserved in cranial cavities of extinct proboscideans.
Section snippets
Materials and methods
Our data are based on direct observations of seven elephant brains, three Asian and four African elephants, Elephas maximus and Loxodonta africana, respectively (Table 1A). Elephant brains listed in Table 1A were obtained within 12–24 h after death. They were removed with tools, such as chain saw, chisels, and hammers for adult elephants, or with a Stryker electric handsaw or a hacksaw for a newly born elephant (Fig. 1A and B). Specimens were originally fixed in formaldehyde or
General observations
Six of the seven captive elephant brains available for our study (Table 1A) were females. African elephants (L. africana) brains comprised 13/22 of all the brains listed in Table 1A and B; the remaining eight brains were of Asian elephant (E. maximus), plus one of unknown genus.
Encased in the bony braincase, the brain of an adult elephant is well protected (Fig. 1A, top). In adult elephants, the sidewalls and roof of the braincase are not all solid bones; they are pneumatized, extensively
Historical and current perspectives
Anatomical studies of elephant brains were conducted by various investigators [1], [10], [19], [32], [44], [45], [46], [55], [61], [62], [63], [72], [73], [74], [77], [79], [80], [81], [87], [99], [109], [119], [122], [129], [130], [131]. Each of these investigators focused on certain areas, or made general observations; the study of Dexler [32] was the most comprehensive. The recent review by Cozzi et al. [22] brought to light the paucity of basic detailed research on elephant brains. The
Acknowledgements
Credits for the brains (or parts of them) of specimens A–G are given in Table 1. These individuals deserve special acknowledgments: veterinarians Dalen Agnew, Ann Duncan, and Cindy Stadler (all from the Detroit Zoological Institute), veterinarians Richard J. Montali (National Zoological Park) and Wynona Schallenberger (Toledo Zoo), and Bucky Steele (Seagoville, Texas)—for providing brain specimens. Charles R. Chaff (Museum of Comparative Zoology, MCZ, at Harvard University, Cambridge, MA, USA)
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