115
epithelium, and from neural crest derived mesenchyme, contributing to dentin and
pulp, ” (Soukup et al. 2008 ). However, recently, very interesting results have been
obtained in experiments with a combination of fate-mapping approaches using
transgenic axolotls. Soukup and co-workers ( 2008 ) showed with strong evidence
the existence of oral teeth derived from both the endoderm and ectoderm. Also the
teeth with a mixed ecto/endodermal origin have been identifi ed. It was proposed
the dominant role for the neural crest mesenchyme over epithelia in axolotl’s tooth
initiation. Also, “ from an evolutionary point of view, that an essential factor in teeth
evolution was the odontogenic capacity of neural crest cells, regardless of possible
‘outside- in’ or ‘inside-out’ infl ux of the epithelium ” (Soukup et al. 2008 ).
Multi-layered true teeth, which include also layers of dentine and enameloid,
were developed by osteichthyan fi sh. (Please, note that detailed description of
diversity and properties of enameloid, enamel, and dentin are represented in a separate Sect. 4.1 below!).
Because of the broad diversity of marine vertebrate oral teeth, I take the liberty
to represent and discuss only teeth with mostly unusual structure (e.g. folded teeth)
and material properties (hypermineralized teeth) in this chapter.
3.2.6.1 Folded Teeth
Among crossopterygians and lower tetrapods as well as in the ichthyosaurs, the
mosasaurs, varanid-like reptiles, actinopterygian Lepisosteus and its closest
relatives, and possibly the primitive diapsid Champsosaurus (Warren and Davey
1992 ; Warren and Turner 2006 ) there are groups that have teeth of peculiar internal
structure, involving an infolding of the special type of dentine –orthodentine- of the
pulp cavity wall. Such orthodentine is called “folded dentine” (plicidentine), and
teeth possessing it are “folded teeth” (Bystrow 1938 , 1939 ; Schultze 1969 , 1970 )
(Fig. 3.12 ). The increase of the number of folds of dentine correlated with the age
of the individual (Bystrow 1938 ). As reviewed by Maxwell, “ the appearance of
dentine folding can be created when radial canals divide the dentine into lobes
(e.g., Eurypodus), or dentine spicules of uneven length project into the pulp cavity
(e.g., Mylobatis) in the absence of external folding, making the morphology of the
pulp cavity alone misleading for predicting the presence of plicidentine, ” (Maxwell
et al. 2011 ).
Are there some adaptive advantages of folded teeth in comparison to classical
true teeth? Following properties are under discussion:
• “increased strength of the tooth base without a large increase in the amount of
mineralized tissue;
• increased fl exibility of the tooth base;
• increased surface area for attachment tissues,” (Maxwell et al. 2011 ; see also
Besmer 1947 ; Peyer 1968 ; Scanlon and Lee 2002 ).
May be plicidentine is the characteristic feature of the teeth observed in large
kinetic-feeding predators (Scanlon and Lee 2002 ; Modesto and Reisz 2008 ).
3.2 Teeth
epithelium, and from neural crest derived mesenchyme, contributing to dentin and
pulp, ” (Soukup et al. 2008 ). However, recently, very interesting results have been
obtained in experiments with a combination of fate-mapping approaches using
transgenic axolotls. Soukup and co-workers ( 2008 ) showed with strong evidence
the existence of oral teeth derived from both the endoderm and ectoderm. Also the
teeth with a mixed ecto/endodermal origin have been identifi ed. It was proposed
the dominant role for the neural crest mesenchyme over epithelia in axolotl’s tooth
initiation. Also, “ from an evolutionary point of view, that an essential factor in teeth
evolution was the odontogenic capacity of neural crest cells, regardless of possible
‘outside- in’ or ‘inside-out’ infl ux of the epithelium ” (Soukup et al. 2008 ).
Multi-layered true teeth, which include also layers of dentine and enameloid,
were developed by osteichthyan fi sh. (Please, note that detailed description of
diversity and properties of enameloid, enamel, and dentin are represented in a separate Sect. 4.1 below!).
Because of the broad diversity of marine vertebrate oral teeth, I take the liberty
to represent and discuss only teeth with mostly unusual structure (e.g. folded teeth)
and material properties (hypermineralized teeth) in this chapter.
3.2.6.1 Folded Teeth
Among crossopterygians and lower tetrapods as well as in the ichthyosaurs, the
mosasaurs, varanid-like reptiles, actinopterygian Lepisosteus and its closest
relatives, and possibly the primitive diapsid Champsosaurus (Warren and Davey
1992 ; Warren and Turner 2006 ) there are groups that have teeth of peculiar internal
structure, involving an infolding of the special type of dentine –orthodentine- of the
pulp cavity wall. Such orthodentine is called “folded dentine” (plicidentine), and
teeth possessing it are “folded teeth” (Bystrow 1938 , 1939 ; Schultze 1969 , 1970 )
(Fig. 3.12 ). The increase of the number of folds of dentine correlated with the age
of the individual (Bystrow 1938 ). As reviewed by Maxwell, “ the appearance of
dentine folding can be created when radial canals divide the dentine into lobes
(e.g., Eurypodus), or dentine spicules of uneven length project into the pulp cavity
(e.g., Mylobatis) in the absence of external folding, making the morphology of the
pulp cavity alone misleading for predicting the presence of plicidentine, ” (Maxwell
et al. 2011 ).
Are there some adaptive advantages of folded teeth in comparison to classical
true teeth? Following properties are under discussion:
• “increased strength of the tooth base without a large increase in the amount of
mineralized tissue;
• increased fl exibility of the tooth base;
• increased surface area for attachment tissues,” (Maxwell et al. 2011 ; see also
Besmer 1947 ; Peyer 1968 ; Scanlon and Lee 2002 ).
May be plicidentine is the characteristic feature of the teeth observed in large
kinetic-feeding predators (Scanlon and Lee 2002 ; Modesto and Reisz 2008 ).
3.2 Teeth