218
Acrodin is enameloid of teleost fi sh. This term was proposed by Ørvig ( 1978 )
for fossil actinopterygian fi shes Nephrotus and Colobodus .
Prelomin is enameloid of holocefalans (members of the Chondrichthyes) (Ørvig
1967 ). This unique whitlockite-based highly mineralized tissue arises only from
mesenchymal cells (Ishiyama et al. 1984 , 1991 ). Also the ability of the mesenchymal cells themselves to be a player in biomineralization of the enamels is an interesting fact. It was reported, that “the initial crystals in prelomin are formed in the
tubular saccules limited by a unit membrane and derived from mesenchymal cells,”
(Sasagawa 2002 ; see also Ishiyama et al. 1991 ).
4.2 Dentine and Dentine-Based Composite
Dentine is formed by two simultaneous processes, in which the odontoblasts are
instrumental—the formation of the collagenous matrix, and mineral crystal formation in this matrix (Linde 1995 ). In other words, dentine is formed centripetally by
the activity of odontoblasts and may be recognized by calcospheritic mineralization
and the presence of odontoblast lacunae and tubules, which house the odontoblastic
body and processes, respectively (see for detail Green 2009 ). The earliest known
vertebrate that preserves tissue with these traits is Anatolepis from the late Cambrian,
approximately 510 million years ago (Young et al. 1996 ). Dentin, which is less
mineralized and less brittle than enamel, is necessary for the support of enamel.
However, human dentine is a hard and brittle mineralized tissue. For example, it is
diffi cult to prepare thin specimens (under 200 nm) of dentine for transmission electron microscope observation without demineralizing them (Miura et al. 2012 ).
Tooth dentine is excellent described in humans (see for review Zaslansky 2008 ).
Probably the best source concerning the special terminology of the paleohistology of early fi sh dentine is the paper of Ørvig ( 1951 ), where corresponding literature on dentine structure has been reviewed. There are also numerous reports (see
Baume 1980 ) on classifi cation of specifi c types of dentine in marine and aquatic
vertebrates like:
– orthodentine as the most common dentine that consists of two distinct layers;
one with parallel tubes contained within an unmineralized “ predentine ” layer at
the dentine-pulp junction, and a second with a mineralized matrix that is composed of intertubular (and sometimes peritubular) dentine (Green 2009 ). The two
main features of orthodentine are as follow: «it is acellular (cell bodies of the
odontoblasts are localized outside of the tissue matrix) and generally tubular,»
(Sire et al. 2009 ). Additionally, “Each odontoblast has an elongate cell process
that extends into the dentine, surrounded by concentric lamellae of matrix forming a series of parallel tubules. Atubular orthodentine was described in fi rstgeneration teeth of non-tetrapods, a feature that has been related to the small size
of these teeth,” (Sire et al. 2009 ; see also Sire et al. 2002 );
– durodentine in devonian Laccognathus panderi fi sh (Schmidt 1948 , 1959 );
4 Fish Scales as Mineral-Based Composites
Acrodin is enameloid of teleost fi sh. This term was proposed by Ørvig ( 1978 )
for fossil actinopterygian fi shes Nephrotus and Colobodus .
Prelomin is enameloid of holocefalans (members of the Chondrichthyes) (Ørvig
1967 ). This unique whitlockite-based highly mineralized tissue arises only from
mesenchymal cells (Ishiyama et al. 1984 , 1991 ). Also the ability of the mesenchymal cells themselves to be a player in biomineralization of the enamels is an interesting fact. It was reported, that “the initial crystals in prelomin are formed in the
tubular saccules limited by a unit membrane and derived from mesenchymal cells,”
(Sasagawa 2002 ; see also Ishiyama et al. 1991 ).
4.2 Dentine and Dentine-Based Composite
Dentine is formed by two simultaneous processes, in which the odontoblasts are
instrumental—the formation of the collagenous matrix, and mineral crystal formation in this matrix (Linde 1995 ). In other words, dentine is formed centripetally by
the activity of odontoblasts and may be recognized by calcospheritic mineralization
and the presence of odontoblast lacunae and tubules, which house the odontoblastic
body and processes, respectively (see for detail Green 2009 ). The earliest known
vertebrate that preserves tissue with these traits is Anatolepis from the late Cambrian,
approximately 510 million years ago (Young et al. 1996 ). Dentin, which is less
mineralized and less brittle than enamel, is necessary for the support of enamel.
However, human dentine is a hard and brittle mineralized tissue. For example, it is
diffi cult to prepare thin specimens (under 200 nm) of dentine for transmission electron microscope observation without demineralizing them (Miura et al. 2012 ).
Tooth dentine is excellent described in humans (see for review Zaslansky 2008 ).
Probably the best source concerning the special terminology of the paleohistology of early fi sh dentine is the paper of Ørvig ( 1951 ), where corresponding literature on dentine structure has been reviewed. There are also numerous reports (see
Baume 1980 ) on classifi cation of specifi c types of dentine in marine and aquatic
vertebrates like:
– orthodentine as the most common dentine that consists of two distinct layers;
one with parallel tubes contained within an unmineralized “ predentine ” layer at
the dentine-pulp junction, and a second with a mineralized matrix that is composed of intertubular (and sometimes peritubular) dentine (Green 2009 ). The two
main features of orthodentine are as follow: «it is acellular (cell bodies of the
odontoblasts are localized outside of the tissue matrix) and generally tubular,»
(Sire et al. 2009 ). Additionally, “Each odontoblast has an elongate cell process
that extends into the dentine, surrounded by concentric lamellae of matrix forming a series of parallel tubules. Atubular orthodentine was described in fi rstgeneration teeth of non-tetrapods, a feature that has been related to the small size
of these teeth,” (Sire et al. 2009 ; see also Sire et al. 2002 );
– durodentine in devonian Laccognathus panderi fi sh (Schmidt 1948 , 1959 );
4 Fish Scales as Mineral-Based Composites