enameloid

{{Short description|Mineralised tissue found in fish}}

Enameloid, also known as durodentine or vitrodentine, is an enamel-like tissue found in fish. It is the primary outer component of shark odontodes (teeth and dermal denticles),{{Cite journal |last=Kawasaki |first=Kazuhiko |last2=Keating |first2=Joseph N. |last3=Nakatomi |first3=Mitsushiro |last4=Welten |first4=Monique |last5=Mikami |first5=Masato |last6=Sasagawa |first6=Ichiro |last7=Puttick |first7=Mark N. |last8=Donoghue |first8=Philip C. J. |last9=Ishiyama |first9=Mikio |date=2021-01-22 |title=Coevolution of enamel, ganoin, enameloid, and their matrix SCPP genes in osteichthyans |url=https://linkinghub.elsevier.com/retrieve/pii/S2589004220312207 |journal=iScience |language=English |volume=24 |issue=1 |doi=10.1016/j.isci.2020.102023 |issn=2589-0042 |pmc=7814152 |pmid=33506188}} and modified forms of enameloid also occur in the teeth and scales of actinopterygian (ray finned) fishes and stem-group gnathostomes (jawed vertebrates). In extinct, armored jawless vertebrates such as heterostracans, enameloid forms the outer component of shell-like dermal armor.{{Cite journal |last=Keating |first=Joseph N. |last2=Marquart |first2=Chloe L. |last3=Donoghue |first3=Philip C. J. |date=2015 |title=Histology of the heterostracan dermal skeleton: Insight into the origin of the vertebrate mineralised skeleton |url=https://onlinelibrary.wiley.com/doi/10.1002/jmor.20370 |journal=Journal of Morphology |language=en |volume=276 |issue=6 |pages=657–680 |doi=10.1002/jmor.20370 |issn=1097-4687 |pmc=4979667 |pmid=25829358}} Although the origin of enameloid is debated, it is probably homologous to dentine rather than true enamel, despite its enamel-like strength and development. The term covers any hyper-mineralized tissue with an organic "scaffold" consisting of ectodermal and ectomesenchymal proteins.{{Cite journal|last=Sire|first=Jean-Yves|last2=Donoghue|first2=Philip C. J.|last3=Vickaryous|first3=Matthews K.|date=2009|title=Origin and evolution of the integumentary skeleton in non-tetrapod vertebrates|url= |journal=Journal of Anatomy|language=en|volume=214|issue=4|pages=409–440|doi=10.1111/j.1469-7580.2009.01046.x|issn=1469-7580|pmc=2736117|pmid=19422423}}{{Cite journal| last1 = Gillis | first1 = J.| last2 = Donoghue | first2 = P.| title = The homology and phylogeny of chondrichthyan tooth enameloid| journal = Journal of Morphology| volume = 268| issue = 1| pages = 33–49| year = 2007| pmid = 17146771| doi = 10.1002/jmor.10501| doi-access = }}{{Cite web|title=Palaeos Vertebrates: Bones: Teeth: Overview-2|url=http://www.palaeos.com/Vertebrates/Bones/Teeth/Teeth2.html|date=2010-09-10|archive-url=https://web.archive.org/web/20100910085445/http://www.palaeos.com/Vertebrates/Bones/Teeth/Teeth2.html|access-date=2020-05-07|archive-date=2010-09-10}}