Architecture of the sperm whale forehead facilitates ramming combat

Olga Panagiotopoulou; Panagiotis Spyridis; Hyab Mehari Abraha; David R Carrier; Todd C Pataky

doi:10.7287/peerj.preprints.1590v1

Architecture of the sperm whale forehead facilitates ramming combat

Olga Panagiotopoulou ¹, Panagiotis Spyridis², Hyab Mehari Abraha¹, David R Carrier³, Todd C Pataky⁴

1 Moving Morphology and Functional Mechanics Laboratory, School of Biomedical Sciences, Faculty of Medicine and Biomedical Sciences, The University of Queensland, Brisbane 4072, Australia

2 Polytropos Ltd, London N1 7JL, United Kingdom

3 Department of Biology, University of Utah, Salt Lake City, UT 84112, United States of America

4 Institute for Fiber Engineering, Department of Bioengineering, Shinshu University, Ueda, Nagano, Japan

DOI: 10.7287/peerj.preprints.1590v1

Published: 2015-12-17
Accepted: 2015-12-17

Subject Areas: Animal Behavior, Evolutionary Studies, Zoology
Keywords: sperm whale, spermaceti junk, ramming impact, finite element analysis, probabilistic simulation, connective tissue partitions

Copyright: © 2015 Panagiotopoulou et al.
Licence: This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ PrePrints) and either DOI or URL of the article must be cited.

Cite this article: Panagiotopoulou O, Spyridis P, Mehari Abraha H, Carrier DR, Pataky TC. 2015. Architecture of the sperm whale forehead facilitates ramming combat. PeerJ PrePrints 3:e1590v1 https://doi.org/10.7287/peerj.preprints.1590v1

Abstract

Herman Melville’s novel Moby Dick was inspired by historical instances in which large sperm whales (Physeter macrocephalus L.) sank 19th century whaling ships by ramming them with their foreheads. The immense forehead of sperm whales is possibly the largest, and one of the strangest, anatomical structures in the animal kingdom. It contains two large oil-filled compartments, known as the “spermaceti organ” and “junk”, that constitute up to one-quarter of body mass and extend one-third of the total length of the whale. Recognized as playing an important role in echolocation, previous studies have also attributed the complex structural configuration of the spermaceti organ and junk to acoustic sexual selection, acoustic prey debilitation, buoyancy control, and aggressive ramming. Of these additional suggested functions, ramming remains the most controversial, and the potential mechanical roles of the structural components of the spermaceti organ and junk in ramming remain untested. Here we explore the aggressive ramming hypothesis using a novel combination of structural engineering principles and probabilistic simulation to determine if the unique structure of the junk significantly reduces stress in the skull during quasi-static impact. Our analyses indicate that the connective tissue partitions within the junk reduce stress across the skull during impact; stress reduction is greatest in the anterior aspect of the skull; and removal of the connective tissue partitions increases stress concentrations on the tip of the skull, possibly making it prone to fracture. Although the unique structure of the junk certainly serves multiple functions, our results are consistent with the hypothesis that the structure also evolved to function as a massive battering ram during male-male competition.