110
Between 18 and 23 equally spaced pair of teeth expanding at the base up from
the rostrum is the characteristic feature of modern Pristis microdon (Seitz 2011 ).
It is suggested that the rostral teeth at the juvenile stage of fi sh development are not
fully erupted and even covered in a sheath of tissue so as not to injure the female.
Sawfi shes use their specialized rostrum in order to obtain benthic invertebrates
and small fi shes in sandy/muddy bottoms. The feeding behaviour is well described
as follow:
“ They move it in a slashing gesture from side-to-side when attaching/stunning
schools of fi sh, as well as for extracting animals such as molluscs and small crustacean
from the benthic sediments ” (Allen 1982 ).
In pristids, the teeth along the saw are not replaced if they are lost. However,
evidence suggests that at least one species of extant saw fi shes may have rotated out
their rostral teeth. This is Schizorhiza (“split root”) a fossil genus that include
Schizorhiza stromeri as a single species. Its fossil remnants are dated as 71 and 65.5
MYR (Kirkland and Aguillón Martínez 2002 ). This animal is unique among all
“saw-snouted” Elasmobranchii because of replacement mechanism for their teeth
based on a continuous serrated cover of tooth enamel localized on the rostrum’s
edge. These teeth with the size about 1–2 cm tall and 4–8 mm wide had a small
triangular or rhomboidal shape at the tip, with sharp cutting edges, and a long forked
peduncle. The new teeth developed inside this fork. The animal also possess the oral
teeth, which were, however, “very small (about 1.5–2.5 mm high and 1–2 mm
wide), with a large and recurved central point and keels at the side that formed tiny
secondary points” (Kirkland and Aguillón Martínez 2002 ).
There are different opinions with regards to origin and types of rostral teeth
dentine. The fi rst form of dentine was probably orthodentine (Miller 1974 ).
However, Shellis and Berkovitz ( 1980 ) reported that that “the osteodentine has a
unique arrangement of matrix collagen fi bres in recent rostral teeth. The dentine is
composed of thick bundles of closely packed, mineralized collagen fi bres orientated parallel with the long axis of the tooth,” (Shellis and Berkovitz ( 1980 )).
Unlike the rostral teeth of modern pristides, the rostral teeth of the cretaceous
Sclerorhynchidae species have a cup with smooth enameloid (see also Sect. 4.1 in
this work).
To my best knowledge, we have no information about dentition mechanisms
in rostral teeth of saw fi shes. However, the fi nding of sawfi sh rostral teeth with
pathological deformities represented in Fig. 3.9 . demonstrate the existence of very
complex biomineralization phenomenon.
3.2.4 Pharyngeal Denticles and Teeth
Pharyngeal denticles were reported for extant placoderms (Johanson and
Smith 2005 ). In contrast to the group of dentate Chondrichthyes, Acanthodii
and Osteichthyes, the fossil placoderms lacks a marginal dentition. It was suggested
that “during evolution, pharyngeal denticles and teeth are independently derived
3 Biocomposites and Mineralized Tissues
Between 18 and 23 equally spaced pair of teeth expanding at the base up from
the rostrum is the characteristic feature of modern Pristis microdon (Seitz 2011 ).
It is suggested that the rostral teeth at the juvenile stage of fi sh development are not
fully erupted and even covered in a sheath of tissue so as not to injure the female.
Sawfi shes use their specialized rostrum in order to obtain benthic invertebrates
and small fi shes in sandy/muddy bottoms. The feeding behaviour is well described
as follow:
“ They move it in a slashing gesture from side-to-side when attaching/stunning
schools of fi sh, as well as for extracting animals such as molluscs and small crustacean
from the benthic sediments ” (Allen 1982 ).
In pristids, the teeth along the saw are not replaced if they are lost. However,
evidence suggests that at least one species of extant saw fi shes may have rotated out
their rostral teeth. This is Schizorhiza (“split root”) a fossil genus that include
Schizorhiza stromeri as a single species. Its fossil remnants are dated as 71 and 65.5
MYR (Kirkland and Aguillón Martínez 2002 ). This animal is unique among all
“saw-snouted” Elasmobranchii because of replacement mechanism for their teeth
based on a continuous serrated cover of tooth enamel localized on the rostrum’s
edge. These teeth with the size about 1–2 cm tall and 4–8 mm wide had a small
triangular or rhomboidal shape at the tip, with sharp cutting edges, and a long forked
peduncle. The new teeth developed inside this fork. The animal also possess the oral
teeth, which were, however, “very small (about 1.5–2.5 mm high and 1–2 mm
wide), with a large and recurved central point and keels at the side that formed tiny
secondary points” (Kirkland and Aguillón Martínez 2002 ).
There are different opinions with regards to origin and types of rostral teeth
dentine. The fi rst form of dentine was probably orthodentine (Miller 1974 ).
However, Shellis and Berkovitz ( 1980 ) reported that that “the osteodentine has a
unique arrangement of matrix collagen fi bres in recent rostral teeth. The dentine is
composed of thick bundles of closely packed, mineralized collagen fi bres orientated parallel with the long axis of the tooth,” (Shellis and Berkovitz ( 1980 )).
Unlike the rostral teeth of modern pristides, the rostral teeth of the cretaceous
Sclerorhynchidae species have a cup with smooth enameloid (see also Sect. 4.1 in
this work).
To my best knowledge, we have no information about dentition mechanisms
in rostral teeth of saw fi shes. However, the fi nding of sawfi sh rostral teeth with
pathological deformities represented in Fig. 3.9 . demonstrate the existence of very
complex biomineralization phenomenon.
3.2.4 Pharyngeal Denticles and Teeth
Pharyngeal denticles were reported for extant placoderms (Johanson and
Smith 2005 ). In contrast to the group of dentate Chondrichthyes, Acanthodii
and Osteichthyes, the fossil placoderms lacks a marginal dentition. It was suggested
that “during evolution, pharyngeal denticles and teeth are independently derived
3 Biocomposites and Mineralized Tissues