97
3.1.1 Whale Bone: Size, Chemistry and Material Properties
Cetaceans (whales, dolphins and porpoises), particularly the Mysticetes (baleen
whales) include some of the largest mammals in the world (Marx 2010 ). One baleen
whale—the blue whale, Balaenoptera can reach 30–37 m long, have a girth of 14 m
and weigh on average between 90 and 181 metric tons (see for review Cook 1973 ;
Perrin et al. 2002 ). Correspondingly, the largest bone in the world belongs to this
animal. For example, the blue whale’s powerful jawbone measures an average of
2.5 m in length and weighs up to 550 kg. Traditionally, bone is seen to exhibit seven
levels of structural hierarchy, with striking self-similarity near the bottom levels of
hierarchy (see for review Zhang et al. 2011 ). However, I suggest that in the case of
giant whale bones we can speak about an additional the mega-level of structural
hierarchy a bone too.
From a materials science perspective, the chemistry, composition, nanostructure,
material properties and biomechanics of diverse whale bones are intriguing.
However, studies on these bones are a challenging task due to the diffi culties of
obtaining statistically relevant samples for comparative studies. Below, I would like
to discuss several properties, which are very specifi c for the structure-function
relationship in whale bones. Included are such phenomena as hypermineralization,
porosity, and the presence of oil.
Ziphiidae, or beaked whales are representatives of odontocetes (toothed whales).
Their feeding behavior is mostly teuthophagous. Some species of ziphiids, with
dive records at more than 1,800 m, are considered to be deep divers (Tyack et al.
2006 ). These cetaceans arrive depths at which prey are detected in near-complete
darkness by echolocation. They distinguished from other odontocetes by the anatomy
of the rostrum that frequently displays extensive changes in the thickness, shape and
density of its constituent bones. For example, “the rostral part of the composite
calvarium bones of an adult male of the ziphiid species, Mesoplodon densirostris ,
yielded among the highest values for density (2.6 g/cm
3 ), mineralization (86.7 %),
and compactness (99 %) yet reported,” (Zioupos et al. 1997 ).
Probably, the extremely high mineralization rate and physical density of the
rostrum (2.612–2.686 g/cm
3
) (De Bufférnil and Casinos 1995 ; Zylberberg et al.
1998 ) in M. densirostris , is determined by a drastic reduction of its collagenous
fi brillar network. According to Zylberberg et al. ( 1998 ), “Mechanical testing of this
bone has shown it to be the stiffest (Young’s modulus up to 49.6 GPa) and hardest
yet examined, as might be expected from its high mineral content,” (Zylberberg
et al. 1998 ).
In these hypermineralized secondary osteons, following features has been reported:
– “lamellae were not observed;
– nor mineralized fi brils;
– the mineral rod fragments are composed of stacked assemblies of crystal plates
elongated along their c axes and parallel to the lengths of the rods;
– the mineral rods can clearly accommodate a much higher density of crystals than
mineralized fi brils commonly found in other bones;
3.1 Bone
3.1.1 Whale Bone: Size, Chemistry and Material Properties
Cetaceans (whales, dolphins and porpoises), particularly the Mysticetes (baleen
whales) include some of the largest mammals in the world (Marx 2010 ). One baleen
whale—the blue whale, Balaenoptera can reach 30–37 m long, have a girth of 14 m
and weigh on average between 90 and 181 metric tons (see for review Cook 1973 ;
Perrin et al. 2002 ). Correspondingly, the largest bone in the world belongs to this
animal. For example, the blue whale’s powerful jawbone measures an average of
2.5 m in length and weighs up to 550 kg. Traditionally, bone is seen to exhibit seven
levels of structural hierarchy, with striking self-similarity near the bottom levels of
hierarchy (see for review Zhang et al. 2011 ). However, I suggest that in the case of
giant whale bones we can speak about an additional the mega-level of structural
hierarchy a bone too.
From a materials science perspective, the chemistry, composition, nanostructure,
material properties and biomechanics of diverse whale bones are intriguing.
However, studies on these bones are a challenging task due to the diffi culties of
obtaining statistically relevant samples for comparative studies. Below, I would like
to discuss several properties, which are very specifi c for the structure-function
relationship in whale bones. Included are such phenomena as hypermineralization,
porosity, and the presence of oil.
Ziphiidae, or beaked whales are representatives of odontocetes (toothed whales).
Their feeding behavior is mostly teuthophagous. Some species of ziphiids, with
dive records at more than 1,800 m, are considered to be deep divers (Tyack et al.
2006 ). These cetaceans arrive depths at which prey are detected in near-complete
darkness by echolocation. They distinguished from other odontocetes by the anatomy
of the rostrum that frequently displays extensive changes in the thickness, shape and
density of its constituent bones. For example, “the rostral part of the composite
calvarium bones of an adult male of the ziphiid species, Mesoplodon densirostris ,
yielded among the highest values for density (2.6 g/cm
3 ), mineralization (86.7 %),
and compactness (99 %) yet reported,” (Zioupos et al. 1997 ).
Probably, the extremely high mineralization rate and physical density of the
rostrum (2.612–2.686 g/cm
3
) (De Bufférnil and Casinos 1995 ; Zylberberg et al.
1998 ) in M. densirostris , is determined by a drastic reduction of its collagenous
fi brillar network. According to Zylberberg et al. ( 1998 ), “Mechanical testing of this
bone has shown it to be the stiffest (Young’s modulus up to 49.6 GPa) and hardest
yet examined, as might be expected from its high mineral content,” (Zylberberg
et al. 1998 ).
In these hypermineralized secondary osteons, following features has been reported:
– “lamellae were not observed;
– nor mineralized fi brils;
– the mineral rod fragments are composed of stacked assemblies of crystal plates
elongated along their c axes and parallel to the lengths of the rods;
– the mineral rods can clearly accommodate a much higher density of crystals than
mineralized fi brils commonly found in other bones;
3.1 Bone