152
fused along two longitudinally opposite ribs, anchoring the embryo in a constant
position within the shell,” (Ferguson 1982 ).
Thus, according to Ferguson ( 1982 ) the “structure of the alligator egg is beautifully
adapted to both its function and the nesting biology of the animal”.
3.4.2 Egg Shells of Sea Birds
Nathusius von Koenigsborn (1821–1899) was the fi rst to employ fossil material in his
study of the eggshell structure (Tyler 1964 ). Serious investigations of fossil eggs and
eggshell remains started in 1923, after the sensational fi nds of the American Museum
of Natural History Expedition in Mongolia (Hirsch 1994 ). The domesticated chicken
( Gallus gallus) has been proposed and used as the classical model for understanding
of the mechanisms of avian eggshell formation and biomineralization. The avian egg
is considered to represent the most advanced amniotic egg in oviparous vertebrates.
The shell is a complex bioceramic that regulates the exchange of metabolic gases and
water, and its properties are exquisitely fi ne-tuned to the environment of a given
species. In their excellent work, Hincke et al. ( 2012 ) reviewed recently eggshell
ultrastructure and microstructure from very modern point of view that summarized
data from recent proteomic, genomic, and transcriptomic analyses. Because there are
numerous excellent books and reviews on avian egg shell morpho logy, structure,
formation and biomineralization including the role of matrix proteins (Romanoff and
Romanoff 1949 ; Tyler 1964 ; Erben and Newesely 1972 ; Board 1982 ; Packard and
Packard 1984 ; Hamilton 1986 ; Arias et al. 1993 ; Mikhailov 1997a , b ; Fernandez
et al. 2001 ; Nys et al. 1999 , 2004 ; Dauphin et al. 2006 ; Rose and Hincke 2009 ;
Hincke et al. 2012 ), I fi nd necessary to discuss here only some principal points.
When complete, the avian eggshell has a well-defi ned structure that is described
as follows from the inside (egg white side) to the outside (external surface): (i) the
mammillae (or mammillary body/cone layer), (ii) the palisades (or palisade layer)
comprising the thickest layer of the shell, and (iii) the transitional vertical crystal
layer. Finally, a thin non-calcifi ed cuticle layer coats the eggshell. The transitional,
inner zone of the cuticle contains spherical aggregates of hydroxyapatite (see for
details Hincke et al. 2012 ).
There are no doubts that different bird species possess egg shells with different
thicknesses. From this point of view, the egg shell of such sea birds as penguins is of
special interest. Penguins use little nesting material on rocky substrates to incubate
their eggs for a long period of time. In spite of these hard conditions, for example, studies on Magellanic Penguins ( Spheniscus magellanicus ) showed that only 2.6 % of
10,023 eggs were broken or cracked. Egg shells for this species are very thick, they
“averaged 0.81 mm without the egg membranes and are at least 56 % thicker than
expected for bird eggs of similar mass,” (Boersma et al. 2004 ). The source of additional
calcium for penguins seems to be the mollusc shells. It was suggested that the “thick
eggshells of penguins, along with selective ingestion of mollusc shells, appears to be an
adaptive response that reduces egg breakage,” (Boersma et al. 2004 ). Principally, the
3 Biocomposites and Mineralized Tissues
fused along two longitudinally opposite ribs, anchoring the embryo in a constant
position within the shell,” (Ferguson 1982 ).
Thus, according to Ferguson ( 1982 ) the “structure of the alligator egg is beautifully
adapted to both its function and the nesting biology of the animal”.
3.4.2 Egg Shells of Sea Birds
Nathusius von Koenigsborn (1821–1899) was the fi rst to employ fossil material in his
study of the eggshell structure (Tyler 1964 ). Serious investigations of fossil eggs and
eggshell remains started in 1923, after the sensational fi nds of the American Museum
of Natural History Expedition in Mongolia (Hirsch 1994 ). The domesticated chicken
( Gallus gallus) has been proposed and used as the classical model for understanding
of the mechanisms of avian eggshell formation and biomineralization. The avian egg
is considered to represent the most advanced amniotic egg in oviparous vertebrates.
The shell is a complex bioceramic that regulates the exchange of metabolic gases and
water, and its properties are exquisitely fi ne-tuned to the environment of a given
species. In their excellent work, Hincke et al. ( 2012 ) reviewed recently eggshell
ultrastructure and microstructure from very modern point of view that summarized
data from recent proteomic, genomic, and transcriptomic analyses. Because there are
numerous excellent books and reviews on avian egg shell morpho logy, structure,
formation and biomineralization including the role of matrix proteins (Romanoff and
Romanoff 1949 ; Tyler 1964 ; Erben and Newesely 1972 ; Board 1982 ; Packard and
Packard 1984 ; Hamilton 1986 ; Arias et al. 1993 ; Mikhailov 1997a , b ; Fernandez
et al. 2001 ; Nys et al. 1999 , 2004 ; Dauphin et al. 2006 ; Rose and Hincke 2009 ;
Hincke et al. 2012 ), I fi nd necessary to discuss here only some principal points.
When complete, the avian eggshell has a well-defi ned structure that is described
as follows from the inside (egg white side) to the outside (external surface): (i) the
mammillae (or mammillary body/cone layer), (ii) the palisades (or palisade layer)
comprising the thickest layer of the shell, and (iii) the transitional vertical crystal
layer. Finally, a thin non-calcifi ed cuticle layer coats the eggshell. The transitional,
inner zone of the cuticle contains spherical aggregates of hydroxyapatite (see for
details Hincke et al. 2012 ).
There are no doubts that different bird species possess egg shells with different
thicknesses. From this point of view, the egg shell of such sea birds as penguins is of
special interest. Penguins use little nesting material on rocky substrates to incubate
their eggs for a long period of time. In spite of these hard conditions, for example, studies on Magellanic Penguins ( Spheniscus magellanicus ) showed that only 2.6 % of
10,023 eggs were broken or cracked. Egg shells for this species are very thick, they
“averaged 0.81 mm without the egg membranes and are at least 56 % thicker than
expected for bird eggs of similar mass,” (Boersma et al. 2004 ). The source of additional
calcium for penguins seems to be the mollusc shells. It was suggested that the “thick
eggshells of penguins, along with selective ingestion of mollusc shells, appears to be an
adaptive response that reduces egg breakage,” (Boersma et al. 2004 ). Principally, the
3 Biocomposites and Mineralized Tissues