A polyphyodont is any animal whose teeth are continually 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 and geckos,[2][3][4] and most other vertebrates, mammals being the main exception, though not absolute.
Growth
editNew, 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 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
editCrocodilia are the only non-mammalian vertebrates with tooth sockets.[6] Alligators 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.[7] Crocodilia are researched for tooth regeneration in humans.[7]
Evolution in mammals
editManatees, elephants and kangaroos 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[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 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”.[9]
See also
edit
References
edit- ^ Buchtová, M.; Štembírek, J.; Glocová, K.; Matalová, E.; Tucker, A.S. (May 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. PMID 22442052. S2CID 206417026.
- ^ "Mechanism of tooth replacement in Leopard geckos]". Archived from the original on 2015-03-12.[self-published source?]
- ^ Fuenzalida, Marcela; Lemus, Susi; Illanes, Julio; Montiel, Enrique; Acuña, Olga; Lemus, David (2000). "Histochemical detection of sugar residues in lizard teeth (Liolaemus gravenhorsti): a lectin-binding study". Biological Research. 33 (3–4): 215–226. doi:10.4067/s0716-97602000000300008. PMID 15696682.
- ^ Gaete, Marcia; Tucker, Abigail S. (3 September 2013). "Organized Emergence of Multiple-Generations of Teeth in Snakes Is Dysregulated by Activation of Wnt/Beta-Catenin Signalling". PLOS ONE. 8 (9): e74484. Bibcode:2013PLoSO...874484G. doi:10.1371/journal.pone.0074484. PMC 3760860. PMID 24019968.
- ^ Whitlock, John A; Richman, Joy M (June 2013). "Biology of tooth replacement in amniotes". International Journal of Oral Science. 5 (2): 66–70. doi:10.1038/ijos.2013.36. PMC 3707075. PMID 23788284.
- ^ LeBlanc, Aaron R. H.; Reisz, Robert R. (4 September 2013). "Periodontal Ligament, Cementum, and Alveolar Bone in the Oldest Herbivorous Tetrapods, and Their Evolutionary Significance". PLOS ONE. 8 (9): e74697. Bibcode:2013PLoSO...874697L. doi:10.1371/journal.pone.0074697. PMC 3762739. PMID 24023957.
- ^ a b 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.; Chuong, Cheng-Ming (28 May 2013). "Specialized stem cell niche enables repetitive renewal of alligator teeth". Proceedings of the National Academy of Sciences. 110 (22): E2009-18. Bibcode:2013PNAS..110E2009W. doi:10.1073/pnas.1213202110. PMC 3670376. PMID 23671090.
- ^ D’Emic, Michael D.; Whitlock, John A.; Smith, Kathlyn M.; Fisher, Daniel C.; Wilson, Jeffrey A. (17 July 2013). "Evolution of High Tooth Replacement Rates in Sauropod Dinosaurs". PLOS ONE. 8 (7): e69235. Bibcode:2013PLoSO...869235D. doi:10.1371/journal.pone.0069235. PMC 3714237. PMID 23874921.
- ^ "Manatee adaptations: the head". Archived from the original on 2016-03-03. Retrieved 2013-11-07.[unreliable source?]
Further reading
edit- Tucker, Abigail S.; Fraser, Gareth J. (January 2014). "Evolution and developmental diversity of tooth regeneration" (PDF). Seminars in Cell & Developmental Biology. 25–26: 71–80. doi:10.1016/j.semcdb.2013.12.013. PMID 24406627.
- Fraser, Gareth J.; Meredith Smith, Moya (15 March 2011). "Evolution of developmental pattern for vertebrate dentitions: an oro-pharyngeal specific mechanism". Journal of Experimental Zoology Part B: Molecular and Developmental Evolution. 316B (2): 99–112. Bibcode:2011JEZB..316...99F. doi:10.1002/jez.b.21387. PMID 21328527.