153
eggs of penguins, guillemots, cormorants, and murres show the highest proportions of
shell mass among the seabirds’ eggshells (Schönwetter 1960 ). The ultrastructure of the
egg shells of some sea birds also possess specifi c pattern. For example, transverse and
tangential ground sections through the egg shells of albatrosses ( Diomedea exulans )
show in the column layer a characteristic “globular pattern” (Schmidt 1967 ).
3.4.3 Conclusion
The eggshell of both marine reptiles and birds is hierarchically structured complex
bioceramic composite made of a mineral part (>95 % CaCO 3 ) and an organic matrix
of very complex composition (1–3.5 %; Hincke et al. 2012 ). The microstructure and
composition of eggshell varies across its thickness. Especially marine reptiles
possess broad variety of egg shells with different physical properties like stiffness
and porosity. Unfortunately, very little attention is still paid to investigations of the
material properties and biomechanics of these unique structures. Eggshells of sea
birds have also been studied mostly from ecological point of view. I am very hopeful
that this situation will be rectifi ed in the near future.
3.5 Biomagnetite in Marine Vertebrates
Abstract Magnetite is the most important magnetic mineral on Earth. It occurs
in continental and oceanic crust as a primary or secondary mineral in igneous,
sedimentary and low- and high-grade metamorphic rocks. Biogenic magnetite, an
example of nanomagnetism, occurs in microorganisms, invertebrates and vertebrates
species. Among the marine vertebrates that use magnetite are fi sh, turtles, sea birds
and cetaceans. Since Lowenstam ( 1962 ) reported biogenic magnetite in the radular
teeth of chitons, the idea that biologically synthesized magnetite particles may form
the core of the animal magnetic sense became the working hypothesis of a number
of behavioural, neurological and physiological studies. For magnetite crystals to
function as magnetoreceptors in animals, the magnetite presumably needs to contact
the nervous system.
Magnetite is a cubic mineral with inverse spinel structure that has the structural
formula Fe
3+ (Fe
2+
Fe
3+ )O 4 , and possess ferromagnetic properties. The unit cell is
represented by eight tetrahedral sites fi lled with Fe
3+ cations and sixteen octahedral
sites, half of which are fi led with Fe
2+ cations and the other half with Fe
3+ cations
(Davila 2005 ). According to Muheim ( 2004 ):
“A magnetic fi eld is a form of stored energy, but in ferrimagnets arises from
microscopic currents associated with electrons in the atoms of permanently magnetic
material. 97–99 % of the Earth’s magnetic fi eld is due to the main fi eld from electric
3.5 Biomagnetite in Marine Vertebrates
eggs of penguins, guillemots, cormorants, and murres show the highest proportions of
shell mass among the seabirds’ eggshells (Schönwetter 1960 ). The ultrastructure of the
egg shells of some sea birds also possess specifi c pattern. For example, transverse and
tangential ground sections through the egg shells of albatrosses ( Diomedea exulans )
show in the column layer a characteristic “globular pattern” (Schmidt 1967 ).
3.4.3 Conclusion
The eggshell of both marine reptiles and birds is hierarchically structured complex
bioceramic composite made of a mineral part (>95 % CaCO 3 ) and an organic matrix
of very complex composition (1–3.5 %; Hincke et al. 2012 ). The microstructure and
composition of eggshell varies across its thickness. Especially marine reptiles
possess broad variety of egg shells with different physical properties like stiffness
and porosity. Unfortunately, very little attention is still paid to investigations of the
material properties and biomechanics of these unique structures. Eggshells of sea
birds have also been studied mostly from ecological point of view. I am very hopeful
that this situation will be rectifi ed in the near future.
3.5 Biomagnetite in Marine Vertebrates
Abstract Magnetite is the most important magnetic mineral on Earth. It occurs
in continental and oceanic crust as a primary or secondary mineral in igneous,
sedimentary and low- and high-grade metamorphic rocks. Biogenic magnetite, an
example of nanomagnetism, occurs in microorganisms, invertebrates and vertebrates
species. Among the marine vertebrates that use magnetite are fi sh, turtles, sea birds
and cetaceans. Since Lowenstam ( 1962 ) reported biogenic magnetite in the radular
teeth of chitons, the idea that biologically synthesized magnetite particles may form
the core of the animal magnetic sense became the working hypothesis of a number
of behavioural, neurological and physiological studies. For magnetite crystals to
function as magnetoreceptors in animals, the magnetite presumably needs to contact
the nervous system.
Magnetite is a cubic mineral with inverse spinel structure that has the structural
formula Fe
3+ (Fe
2+
Fe
3+ )O 4 , and possess ferromagnetic properties. The unit cell is
represented by eight tetrahedral sites fi lled with Fe
3+ cations and sixteen octahedral
sites, half of which are fi led with Fe
2+ cations and the other half with Fe
3+ cations
(Davila 2005 ). According to Muheim ( 2004 ):
“A magnetic fi eld is a form of stored energy, but in ferrimagnets arises from
microscopic currents associated with electrons in the atoms of permanently magnetic
material. 97–99 % of the Earth’s magnetic fi eld is due to the main fi eld from electric
3.5 Biomagnetite in Marine Vertebrates