125
According to Espinoza and Mann ( 2000 ).
“ killer whale teeth show two slight peripheral indentations. The dentine is
deposited in a progressive laminar fashion. As a result of this laminar deposition,
killer and sperm whale teeth will show prominent concentric dentine rings in
cross- section. Killer whale teeth may also display a faint rosette pattern in the dentine
cross-section. The dentine is separated from the cementum by a clearly defi ned
transition ring, ” (Espinoza and Mann 2000 ).
Rhythmically accreted growth structures (“growth layer groups” GLG) (Perrin
and Myrick 1981 ), analogous to tree rings, are visible in longitudinal cross sections
of the toothed whale teeth. As physeterid teeth grow continuously over ontogeny,
these structures can be used to ascertain the age of the animal at death (see for
review Scheffer and Myrick 1980 ; Evans and Robertson 2001 ; Amano et al. 2011 ).
The method of age estimation of toothed cetaceans, based on counts of growth layer
groups (GLGs,) of tissue in the teeth, was introduced 35 years ago (Nishiwaki and
Yagi 1953 ). Since then GLG counting has become an important procedure when
studying the age-related biology of odontocete populations. The dark and light
GLG became visible as opaque layers by transmitted light, however, as translucent
by refl ected light. Because of the anisotropic features of the translucent layer, it was
concluded (Scheffer and Myrick 1980 ) that it possesses crystalline structure. It was
also observed that, the thickness of the newest layer tends to decrease in correlation
with increasing age. Interestingly that the layer thickness in females is slightly
lower than in males. Possibly, the GLG possess paleoclimatic and nutritional information too. The authors reported that:
“ The dark band layer seems to be accumulated as the result of a good nutritious
condition. Partly from these measurements of seasonal progression in thickness of
dentin and partly from study of marked whales, it was concluded that only one dark
layer a year is deposited, ” (Scheffer and Myrick 1980 ).
Sperm whales are related to widely distributed cetaceans, which habituate diverse
aquatic niches including tropical waters and areas near the polar ice (Rice 1989 ).
Meat, bone and spermaceti oil were the reasons for hunting on these animals in
tropical and subtropical waters especially in the 18th century. Partially pelagic sperm
whaling had declined by the 1900s. However it started again after World War II. The
destruction of the sperm whales population continued until the international moratorium on whaling went into effect in 1986 (Evans 1987 ). Thus, more than 500,000
specimens were killed.
Finally, I would like to insert here the critical view made by Pichler and co- authors
( 2001 ) as follow:
“ Sperm whaling was a dangerous occupation, as depicted in paintings, woodcuts,
and engravings of the era. For both commercial whalers and the indigenous people
who used stranded animals as a resource, sperm whale teeth were considered valuable
trophies or status symbols. Among sailors, the intricate engraving of sperm
whale teeth and other ivory developed into a distinctive art form known as scrimshaw.
Today, large quantities of scrimshaw and carved indigenous artefacts are found in
museums and private collections throughout the world. These collections represent
an almost unprecedented historical population sample for a marine species.
3.2 Teeth
According to Espinoza and Mann ( 2000 ).
“ killer whale teeth show two slight peripheral indentations. The dentine is
deposited in a progressive laminar fashion. As a result of this laminar deposition,
killer and sperm whale teeth will show prominent concentric dentine rings in
cross- section. Killer whale teeth may also display a faint rosette pattern in the dentine
cross-section. The dentine is separated from the cementum by a clearly defi ned
transition ring, ” (Espinoza and Mann 2000 ).
Rhythmically accreted growth structures (“growth layer groups” GLG) (Perrin
and Myrick 1981 ), analogous to tree rings, are visible in longitudinal cross sections
of the toothed whale teeth. As physeterid teeth grow continuously over ontogeny,
these structures can be used to ascertain the age of the animal at death (see for
review Scheffer and Myrick 1980 ; Evans and Robertson 2001 ; Amano et al. 2011 ).
The method of age estimation of toothed cetaceans, based on counts of growth layer
groups (GLGs,) of tissue in the teeth, was introduced 35 years ago (Nishiwaki and
Yagi 1953 ). Since then GLG counting has become an important procedure when
studying the age-related biology of odontocete populations. The dark and light
GLG became visible as opaque layers by transmitted light, however, as translucent
by refl ected light. Because of the anisotropic features of the translucent layer, it was
concluded (Scheffer and Myrick 1980 ) that it possesses crystalline structure. It was
also observed that, the thickness of the newest layer tends to decrease in correlation
with increasing age. Interestingly that the layer thickness in females is slightly
lower than in males. Possibly, the GLG possess paleoclimatic and nutritional information too. The authors reported that:
“ The dark band layer seems to be accumulated as the result of a good nutritious
condition. Partly from these measurements of seasonal progression in thickness of
dentin and partly from study of marked whales, it was concluded that only one dark
layer a year is deposited, ” (Scheffer and Myrick 1980 ).
Sperm whales are related to widely distributed cetaceans, which habituate diverse
aquatic niches including tropical waters and areas near the polar ice (Rice 1989 ).
Meat, bone and spermaceti oil were the reasons for hunting on these animals in
tropical and subtropical waters especially in the 18th century. Partially pelagic sperm
whaling had declined by the 1900s. However it started again after World War II. The
destruction of the sperm whales population continued until the international moratorium on whaling went into effect in 1986 (Evans 1987 ). Thus, more than 500,000
specimens were killed.
Finally, I would like to insert here the critical view made by Pichler and co- authors
( 2001 ) as follow:
“ Sperm whaling was a dangerous occupation, as depicted in paintings, woodcuts,
and engravings of the era. For both commercial whalers and the indigenous people
who used stranded animals as a resource, sperm whale teeth were considered valuable
trophies or status symbols. Among sailors, the intricate engraving of sperm
whale teeth and other ivory developed into a distinctive art form known as scrimshaw.
Today, large quantities of scrimshaw and carved indigenous artefacts are found in
museums and private collections throughout the world. These collections represent
an almost unprecedented historical population sample for a marine species.
3.2 Teeth