{{Short description|Extinct genus of cartilaginous fishes}} {{Automatic taxobox | fossil_range = {{fossil range|93.9|66.0|latest=47.8|Turonian-Maastrichtian|PS=(possible Paleogene occurrences)}} | image = Myledaphus bipartatus (guitarfish).jpg | image_caption = ''Myledaphus bipartitus'' | taxon = Myledaphus | authority = Cope, 1876<ref name="Cope 1876">{{cite journal |last=Cope |first=E.D. |date=1876 |title=Descriptions of some vertebrate remains from the Fort Union beds of Montana |journal=Proceedings of the Academy of Natural Sciences of Philadelphia |volume=28 |pages=248–261 |url=https://www.biodiversitylibrary.org/item/84760#page/278/mode/1up }}</ref> | type_species = †'''''Myledaphus bipartitus''''' | type_species_authority = Cope, 1876 | subdivision_ranks = Other species | subdivision = *†''Myledaphus tritus'' <br/><small>Nessov in Nessov & Udovitschenko, 1986<ref name="Nessov & Udovitschenko 1986">{{cite journal |last1=Nessov |first1=L.A. |last2=Udovitschenko |first2=N.I. |date=1986 |title=Novyye nakhodki ostatkov pozvonochnykh mela i paleogena Sredney Azii [New findings of vertebrate remains from the Cretaceous and Paleogene of Central Asia] |journal=Voprosy Paleontologii |volume=9 |pages=129–136 |url=https://www.researchgate.net/publication/283694665}}</ref></small> *†''Myledaphus pustulosus'' <br/><small>Cook, Newbrey, Brinkman, & Kirkland, 2014<ref name="Cook et al. 2014">{{cite journal |last1=Cook |first1=T.D. |last2=Newbrey |first2=M.G. |last3=Brinkman |first3=D.B. |last4=Kirkland |first4=J.I. |date=2014 |title=Euselachians from the freshwater deposits of the Hell Creek Formation of Montana |journal=Geological Society of America Special Paper |volume=503 |pages=229–246 |doi=10.1130/2014.2503(08)|isbn=978-0-8137-2503-1 }}</ref></small> *†''Myledaphus araucanus'' <br/><small>Otero, 2019<ref name="Otero 2019">{{cite journal |last=Otero |first=R.A. |date=2019 |title=''Myledaphus araucanus'' sp. nov. (Batomorphi, Rajiformes ''incertae sedis''), a new Late Cretaceous ray from the austral Pacific, and first occurrence of the genus in the Southern Hemisphere |journal=Cretaceous Research |volume=100 |pages=82–90 |doi=10.1016/j.cretres.2019.03.025|bibcode=2019CrRes.100...82O }}</ref></small> }}
'''''Myledaphus''''' is an extinct genus of guitarfish. It currently contains four valid species found in North America (''M. bipartitus'', ''M. pustulosus''), South America (''M. araucanus''), and Central Asia (''M. tritus'').<ref name="Otero 2019"/> It is confirmed to have lived during the Late Cretaceous, with possible occurrences in the Paleocene and early Eocene.<ref name="Cook et al. 2014"/><ref name="Cappetta 2012">{{cite book |last=Cappetta |first=H. |date=2012 |title=Handbook of Paleoichthyology. Volume 3E. Chondrichthyes. Mesozoic and Cenozoic Elasmobranchii: Teeth. |location=Munich |publisher=Verlag Dr. Friedrich Pfeil |isbn=978-3-89937-148-2}}</ref> While the genus is mostly known from teeth, two partial skeletons of ''M. bipartitus'' have been found in the Dinosaur Park Formation of Alberta.<ref name="Neuman & Brinkman 2005">{{cite book |last1=Neuman |first1=A.G. |last2=Brinkman |first2=D.B. |date=2005 |chapter=Fishes of the fluvial beds |editor-last1=Currie |editor-first1=P.J. |editor-last2=Koppelhus |editor-first2=E.B. |title=Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed |location=Bloomington, IN |publisher=Indiana University Press |pages=167–185 |isbn=978-0253345950 |chapter-url=https://www.researchgate.net/publication/287664210 }}</ref>
== Biology == ''Myledaphus'' remains have been found both in marine and fluvial (freshwater) deposits, suggesting it could tolerate a range of salinity.<ref name=":0">Hoffman, Brian L. et al. “Dental Structure of the Late Cretaceous (Maastrichtian) Guitarfish (Neoselachii: Batoidea) Myledaphus pustulosus from the Hell Creek Formation of Garfield County, Montana.” ''Transactions of the Kansas Academy of Science'' 121 (2018): 279 - 296.</ref> This genus was able to move into the North American continent due to an intercontinental seaway flood that happened later on in the cretaceous period.<ref>{{Cite journal |last=Gates |first=Terry A. |last2=Gorscak |first2=Eric |last3=Makovicky |first3=Peter J. |date=2019-01-22 |title=New sharks and other chondrichthyans from the latest Maastrichtian (Late Cretaceous) of North America |url= |journal=Journal of Paleontology |volume=93 |issue=3 |pages=512–530 |doi=10.1017/jpa.2018.92 |issn=0022-3360}}</ref> In the Hell Creek Formation, composed predominantly of floodplain and riverine deposits, ''Myledaphus'' teeth are very common, accounting for a significant fraction of vertebrate remains found in microsites.<ref name=":0" />
''Myledaphus'' has a durophagus dentition with blunt, polygonal-shaped (hexagonal to rhombic) teeth tessellated into a pavement suited for crushing and grinding hard-bodied prey. Their tooth shape are commonnly described as ray teeth.<ref>{{Cite journal |last=Otero |first=Rodrigo A. |date=August 2019 |title=Myledaphus araucanus sp. nov. (Batomorphi, Rajiformes incertae sedis), a new Late Cretaceous ray from the austral Pacific, and first occurrence of the genus in the Southern Hemisphere |url=https://doi.org/10.1016/j.cretres.2019.03.025 |journal=Cretaceous Research |volume=100 |pages=82–90 |doi=10.1016/j.cretres.2019.03.025 |issn=0195-6671|url-access=subscription }}</ref> Many of their teeth show wear consistent with feeding on mollusks, which were common in the rivers of North America during the Late Cretaceous.<ref name=":0" />
''Myledaphus'' also have other traits aside from their teeth that can help identify them. Many of their fossils exhibit very similar shapes such as having "large pectoral fins that do not expand anterior to the eyes" but actually they serve to " form an angular disk that expands caudually".<ref>{{Cite journal |last=Wilson |first=Alycia E. |last2=Newbrey |first2=Michael G. |last3=Brinkman |first3=Donald B. |last4=Cook |first4=Todd D. |last5=Neuman |first5=Andrew G. |date=September 2013 |title=Age and growth in ''Myledaphus bipartitus'', a Late Cretaceous freshwater guitarfish from Alberta, Canada |url=https://doi.org/10.1139/cjes-2013-0001 |journal=Canadian Journal of Earth Sciences |volume=50 |issue=9 |pages=930–944 |doi=10.1139/cjes-2013-0001 |issn=0008-4077|url-access=subscription }}</ref>
==References== {{Reflist|}}
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Category:Cretaceous cartilaginous fish Category:Prehistoric cartilaginous fish genera Category:Cretaceous fish of Asia Category:Cretaceous fish of North America Category:Bissekty Formation Category:Dinosaur Park Formation Category:Laramie Formation Category:Milk River Formation Category:Ojo Alamo Formation Category:Taxa named by Edward Drinker Cope Category:Fossil taxa described in 1876 Category:Fossils of Alberta Category:Fossils of Canada Category:Fossils of the United States Category:Fossils of Uzbekistan Category:Hell Creek fauna