A polyphyodont is any animal whose teeth are continually replaced. In contrast, are characterized by having only two successive sets of teeth.
Polyphyodonts include most toothed fishes (most notably ), many such as and ,
Growth
New, permanent teeth grow in the jaws, usually under or just behind the old tooth, from
in the
dental lamina.
Young animals typically have a full set of teeth when they hatch; there is no tooth change in the egg. Within days, tooth replacement begins, usually in the back of the jaw continuing forward like a wave. On average a tooth is replaced every few months.
Crocodilia
Crocodilia are the only non-mammalian vertebrates with
.
grow a successional tooth (a small replacement tooth) under each mature functional tooth for replacement once a year, each tooth being replaced up to 50 times in the alligator's life.
Crocodilia are researched for tooth regeneration in humans.
Evolution in mammals
Manatees,
elephant and
kangaroo are unusual among mammals because they are polyphyodonts, in contrast to most other mammals which replace their teeth only once in their lives (diphyodont). Although most other extant mammals are not polyphyodont, mammalian ancestors were. During the evolution of
Therapsida, there was a period during which mammals were so small and short-lived that wear on the teeth yielded no significant selection pressure to constantly replace them. Instead, mammals evolved different types of teeth which formed a unit able to crack the exoskeleton of
arthropods. Molars came later in their evolution (as earlier in
cerapods and
Diplodocus). Mammals chew (
masticate) their food which requires a set of firmly attached, strong teeth and a "full" tooth row without gaps.
The manatees have no incisor or canine teeth, just a set of cheek teeth, which are not clearly differentiated into molars and . These teeth are continuously replaced throughout their life with new teeth growing at the rear as older teeth fall out from farther forward in the mouth, a process known as "hind molar progression" or "marching molars".
See also
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Regeneration (biology)
-
Regenerative medicine
-
Regenerative endodontics
-
Schultz's rule
-
Sinoconodon
-
Squamata
-
Animal tooth development
Further reading
