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A '''polyphyodont''' {{IPAc-en|ˌ|p|ä|l|i-|ˈ|f|ī|ə|ˌ|d|ä|n|t}} is an animal whose [[tooth (animal)|teeth]] are continuously replaced. In contrast, [[diphyodont]]s are characterized by having only two successive sets of teeth.<ref name=Buchtova>{{cite journal|last=Buchtova|first=M.|coauthors=Stembirek, J.; Glocova, K.; Matalova, E.; Tucker, A. S.|title=Early Regression of the Dental Lamina Underlies the Development of Diphyodont Dentitions|journal=Journal of Dental Research|year=2012|volume=91|issue=5|pages=491–498|doi=10.1177/0022034512442896}}</ref>
A '''polyphyodont''' {{IPAc-en|ˌ|p|ä|l|i-|ˈ|f|ī|ə|ˌ|d|ä|n|t}} is an animal whose [[tooth (animal)|teeth]] are continuously replaced. In contrast, [[diphyodont]]s are characterized by having only two successive sets of teeth.<ref name=Buchtova>{{cite journal|last=Buchtova|first=M.|coauthors=Stembirek, J.; Glocova, K.; Matalova, E.; Tucker, A. S.|title=Early Regression of the Dental Lamina Underlies the Development of Diphyodont Dentitions|journal=Journal of Dental Research|year=2012|volume=91|issue=5|pages=491–498|doi=10.1177/0022034512442896}}</ref>


Polyphyodonts include most toothed fishes, many reptiles such as [[crocodile]]s, [[gecko]]s,<ref>[http://www.devbio.biology.gatech.edu/?page_id=3229 Mechanism of tooth replacement in Leopard geckos]</ref><ref name=FUENZALIDA2000>{{cite journal|last=FUENZALIDA|first=MARCELA|coauthors=LEMUS, SUSI; ILLANES, JULIO; MONTIEL, ENRIQUE; ACUÑA, OLGA; LEMUS, DAVID|title=Histochemical detection of sugar residues in lizard teeth (Liolaemus gravenhorsti): a lectin-binding study|journal=Biological Research|year=2000|volume=33|issue=3-4|doi=10.4067/S0716-97602000000300008|url=http://www.scielo.cl/scielo.php?pid=S0716-97602000000300008&script=sci_arttext}}</ref><ref name=Gaete2013>{{cite journal|last=Gaete|first=Marcia|coauthors=Tucker, Abigail S.; Schubert, Michael|title=Organized Emergence of Multiple-Generations of Teeth in Snakes Is Dysregulated by Activation of Wnt/Beta-Catenin Signalling|journal=PLoS ONE|year=2013|volume=8|issue=9|pages=e74484|doi=10.1371/journal.pone.0074484|url=http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0074484}}</ref> and most other vertebrates, mammals being the main exception. New, permanent teeth grow in the jaws, usually under or just behind the old tooth, from [[stem cell]]s in the [[dental lamina]].<ref>[http://www.nature.com/ijos/journal/v5/n2/full/ijos201336a.html Biology of tooth replacement in amniotes]</ref> Young animals typically have a full set of teeth when they hatch; there is no teeth 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.
Polyphyodonts include most toothed fishes, many reptiles such as [[crocodile]]s, [[gecko]]s,<ref>[http://www.devbio.biology.gatech.edu/?page_id=3229 Mechanism of tooth replacement in Leopard geckos]</ref><ref name=FUENZALIDA2000>{{cite journal|last=Fuenzalida|first=Marcela|coauthors=Lemus, Susi; Illanes, Julio; Montiel, Enrique; Acuña, Olga; Lemus, David|title=Histochemical detection of sugar residues in lizard teeth (''Liolaemus gravenhorsti''): a lectin-binding study|journal=Biological Research|year=2000|volume=33|issue=3-4|doi=10.4067/S0716-97602000000300008|url=http://www.scielo.cl/scielo.php?pid=S0716-97602000000300008&script=sci_arttext}}</ref><ref name=Gaete2013>{{cite journal|last=Gaete|first=Marcia|coauthors=Tucker, Abigail S.; Schubert, Michael|title=Organized Emergence of Multiple-Generations of Teeth in Snakes Is Dysregulated by Activation of Wnt/Beta-Catenin Signalling|journal=PLoS ONE|year=2013|volume=8|issue=9|pages=e74484|doi=10.1371/journal.pone.0074484|url=http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0074484}}</ref> and most other vertebrates, mammals being the main exception. New, permanent teeth grow in the jaws, usually under or just behind the old tooth, from [[stem cell]]s in the [[dental lamina]].<ref name=Whitlock>{{cite journal|last=Whitlock|first=John A|coauthors=Richman, Joy M|title=Biology of tooth replacement in amniotes|journal=International Journal of Oral Science|year=2013|volume=5|issue=2|pages=66–70|doi=10.1038/ijos.2013.36|url=http://www.nature.com/ijos/journal/v5/n2/full/ijos201336a.html}}</ref> Young animals typically have a full set of teeth when they hatch; there is no teeth 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]] are the only non-mammalian vertebrates with [[tooth socket]]s.<ref>[http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0074697 Periodontal ligament, cementum, and alveolar bone in the oldest Herbivorous tetrapods, and their evolutionary significance ]</ref> [[Alligators]] grow up to 50 times a successional tooth (a small replacement tooth) under each mature functional tooth for replacement once a year.<ref>{{cite journal |author= Wu, Ping; Wu, Xiaoshan; Jiang, Ting-Xin; Elsey, Ruth M.; Temple, Bradley L.; Divers, Stephen J.; Glenn, Travis C.; Yuan, Kuo; Chen, Min-Huey; Widelitz, Randall B.; Chuon, Cheng-Ming |year=2013 |title=Specialized stem cell niche enables repetitive renewal of alligator teeth |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=110 |issue=22 |pages=E2009–E2018 |doi=10.1073/pnas.1213202110 |url=http://www-hsc.usc.edu/~cmchuong/2013AllTooth.pdf }}</ref>
[[Crocodilia]] are the only non-mammalian vertebrates with [[tooth socket]]s.<ref name=LeBlanc>{{cite journal|last=LeBlanc|first=Aaron R. H.|coauthors=Reisz, Robert R.; Viriot, Laurent|title=Periodontal Ligament, Cementum, and Alveolar Bone in the Oldest Herbivorous Tetrapods, and Their Evolutionary Significance|journal=PLoS ONE|year=2013|volume=8|issue=9|pages=e74697|doi=10.1371/journal.pone.0074697|url=http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0074697}}</ref> [[Alligators]] grow up to 50 times a successional tooth (a small replacement tooth) under each mature functional tooth for replacement once a year.<ref>{{cite journal |author= Wu, Ping; Wu, Xiaoshan; Jiang, Ting-Xin; Elsey, Ruth M.; Temple, Bradley L.; Divers, Stephen J.; Glenn, Travis C.; Yuan, Kuo; Chen, Min-Huey; Widelitz, Randall B.; Chuon, Cheng-Ming |year=2013 |title=Specialized stem cell niche enables repetitive renewal of alligator teeth |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=110 |issue=22 |pages=E2009–E2018 |doi=10.1073/pnas.1213202110 |url=http://www-hsc.usc.edu/~cmchuong/2013AllTooth.pdf }}</ref>


==Evolution in mammals==
==Evolution in mammals==


[[Kangaroos]], [[elephants]] and [[manatees]] 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 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]]. [[Molar (tooth)|Molar]]s came later in their evolution (as earlier in ''[[cerapoda]]'' and ''[[diplodocus]]''<ref>[http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0069235 Evolution of high tooth replacement rates in sauropod dinosaurs]</ref>). Mammals chew ([[masticate]]) their food which requires a set of firmly attached, strong teeth and a "full" tooth row without gaps.
[[Kangaroos]], [[elephants]] and [[manatees]] 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 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]]. [[Molar (tooth)|Molar]]s came later in their evolution (as earlier in ''[[cerapoda]]'' and ''[[diplodocus]]''<ref name=D’Emic2013>{{cite journal|last=D’Emic|first=Michael D.|coauthors=Whitlock, John A.; Smith, Kathlyn M.; Fisher, Daniel C.; Wilson, Jeffrey A.; Evans, Alistair Robert|title=Evolution of High Tooth Replacement Rates in Sauropod Dinosaurs|journal=PLoS ONE|year=2013|volume=8|issue=7|pages=e69235|doi=10.1371/journal.pone.0069235|url=http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0069235}}</ref>). 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 [[premolar]]s. These teeth are continuously replaced throughout 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”.<ref>[http://www.learner.org/jnorth/tm/manatee/AdaptationsHead.html Manatee adaptations: the head]</ref>
The manatees have no incisor or canine teeth, just a set of cheek teeth, which are not clearly differentiated into molars and [[premolar]]s. These teeth are continuously replaced throughout 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”.<ref>[http://www.learner.org/jnorth/tm/manatee/AdaptationsHead.html Manatee adaptations: the head]</ref>
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==References==
==References==
{{reflist}}
{{reflist|2}}


[[Category:Fish anatomy]]
[[Category:Fish anatomy]]

Revision as of 22:29, 21 December 2013

The teeth of a kangaroo, an example of a polyphodont

A polyphyodont /ˌp[invalid input: 'ä']l[invalid input: 'i-']ˈf[invalid input: 'ī']əˌd[invalid input: 'ä']nt/ is an animal whose teeth are continuously replaced. In contrast, diphyodonts are characterized by having only two successive sets of teeth.[1]

Polyphyodonts include most toothed fishes, many reptiles such as crocodiles, geckos,[2][3][4] and most other vertebrates, mammals being the main exception. New, permanent teeth grow in the jaws, usually under or just behind the old tooth, from stem cells in the dental lamina.[5] Young animals typically have a full set of teeth when they hatch; there is no teeth 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 are the only non-mammalian vertebrates with tooth sockets.[6] Alligators grow up to 50 times a successional tooth (a small replacement tooth) under each mature functional tooth for replacement once a year.[7]

Evolution in mammals

Kangaroos, elephants and manatees 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 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 cerapoda and diplodocus[8]). 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 premolars. These teeth are continuously replaced throughout 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”.[9]

See also

References

  1. ^ Buchtova, M. (2012). "Early Regression of the Dental Lamina Underlies the Development of Diphyodont Dentitions". Journal of Dental Research. 91 (5): 491–498. doi:10.1177/0022034512442896. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  2. ^ Mechanism of tooth replacement in Leopard geckos
  3. ^ Fuenzalida, Marcela (2000). "Histochemical detection of sugar residues in lizard teeth (Liolaemus gravenhorsti): a lectin-binding study". Biological Research. 33 (3–4). doi:10.4067/S0716-97602000000300008. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  4. ^ Gaete, Marcia (2013). "Organized Emergence of Multiple-Generations of Teeth in Snakes Is Dysregulated by Activation of Wnt/Beta-Catenin Signalling". PLoS ONE. 8 (9): e74484. doi:10.1371/journal.pone.0074484. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: unflagged free DOI (link)
  5. ^ Whitlock, John A (2013). "Biology of tooth replacement in amniotes". International Journal of Oral Science. 5 (2): 66–70. doi:10.1038/ijos.2013.36. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  6. ^ LeBlanc, Aaron R. H. (2013). "Periodontal Ligament, Cementum, and Alveolar Bone in the Oldest Herbivorous Tetrapods, and Their Evolutionary Significance". PLoS ONE. 8 (9): e74697. doi:10.1371/journal.pone.0074697. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: unflagged free DOI (link)
  7. ^ Wu, Ping; Wu, Xiaoshan; Jiang, Ting-Xin; Elsey, Ruth M.; Temple, Bradley L.; Divers, Stephen J.; Glenn, Travis C.; Yuan, Kuo; Chen, Min-Huey; Widelitz, Randall B.; Chuon, Cheng-Ming (2013). "Specialized stem cell niche enables repetitive renewal of alligator teeth" (PDF). Proceedings of the National Academy of Sciences of the United States of America. 110 (22): E2009–E2018. doi:10.1073/pnas.1213202110.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  8. ^ D’Emic, Michael D. (2013). "Evolution of High Tooth Replacement Rates in Sauropod Dinosaurs". PLoS ONE. 8 (7): e69235. doi:10.1371/journal.pone.0069235. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: unflagged free DOI (link)
  9. ^ Manatee adaptations: the head
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