Notes on the brain and encephalization quotient of two sperm whales with a synthesis of the literature and indications of a new method of extraction

Abstract

The sperm whale (<em>Physeter</em> <em>macrocephalus</em>, Linnaeus 1758) possesses the largest brain that ever existed. Relatively few authors have dealt with it and the available descriptions are heterogeneous, with only few data about brain weight or gross anatomy. In fact the central nervous system of large cetaceans is quite difficult to obtain, given the huge body size and the low frequency of strandings of recently dead individuals. Furthermore, since the skull of the sperm whale underwent an extreme transformation for the accommodation of the spermaceti organ, the cranial cavity is surrounded by thick layers of bone and thus difficult to reach under field conditions. We recently had the chance to extract the brain from two stranded sperm whales whose bodies were in good condition. In the present note we describe the main macroscopic characteristics of the sperm whale brain, including its weight and Encephalization Quotient, review the available literature, and describe a possible new approach to the removal and preservation of the organ under field conditions.

Analysis of mercury and methylmercury concentrations, and selenium:mercury molar ratios for a toxicological assessment of sperm whales (Physeter macrocephalus) in the most recent stranding event along the Adriatic coast (Southern Italy, Mediterranean Sea)

“…However, wildlife monitoring programs usually only measure liver and kidney Hg concentrations and there is very little data on Hg concentrations in the brain, which is critical for assessing the risk of Hg neurotoxicity. In particular, there is no data about T-Hg and MeHg in sperm whale brains to compare with our findings, possibly due to the problems associated with tissue sampling of lar-ge marine animals, especially under the critical field conditions in the event of stranding (Povinelli et al, 2014). We found that T-Hg and Se levels increase with age (Table 2 and Fig.…”

Comparison of Dolphins' Body and Brain Measurements with Four Other Groups of Cetaceans Reveals Great Diversity

“…However, there is great sexual dimorphism in sperm whales. The EQ of female sperm whales is higher than that of male sperm whales and also higher than equivalent-sized mysticetes [Povinelli et al, 2014]. According to Montgomery et al [2013], the mysticete whales experienced more body mass increase than did Odontoceti.…”

Multivariate Meta-Analysis of Brain-Mass Correlations in Eutherian Mammals

“…In our data set some values are referred only to a single individual, which was the case for, e.g., the blue whale B. musculus (Jansen, 1953 ). However, it was shown for some mammalian groups that there are high intraspecific and sex specific variations regarding brain mass and body mass (Miller and Corsellis, 1977 ; Baron et al, 1996 ; Cozzi et al, 2014 ; Povinelli et al, 2014 ). We are aware of the fact that the intraspecific variations of RB and EQ may alter our statistical results but this discussion can only be addressed when more data will be available in the future.…”