Data from: Architecture of the sperm whale forehead facilitates ramming combat

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 in the junk reduce von
Mises stresses across the skull and the load-redistribution functionality
of the former is insensitive to tissue material parameters, the thickness
of the partitions, and variations in the location and angle of the applied
load. Absence of the connective tissue partitions increases skull
stresses, particularly in the rostral aspect of the upper jaw, further
hinting of the important role the architecture of the junk may play in
ramming events. Our study also found that impact loads on the spermaceti
organ generate lower skull stresses than an impact on the junk.
Nevertheless, whilst an impact on the spermaceti organ would reduce skull
stresses, it would also cause high compressive stresses on the anterior
aspect of the organ and the connective tissue case, possibly making these
structures more prone to failure. This outcome, coupled with the facts
that the spermaceti organ houses sensitive and essential sonar producing
structures and the rostral portion of junk, rather than the spermaceti
organ, is frequently a site of significant scarring in mature males
suggest that whales avoid impact with the spermaceti organ. 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.