{{Short description|Fossil genus of fishes}} {{Automatic taxobox | fossil_range = {{fossil range|Sinemurian|Danian}} | image = Sphenodus nitidus 4.jpg | image_caption = Skeleton of ''Sphenodus nitidus'' (SMNS 96844-7) from the Late Jurassic of Germany | image2 = Sphenodus nitidus tooth.jpg | image2_caption = Tooth of ''Sphenodus nitidus'' | taxon = Sphenodus | authority = Agassiz, 1843 | type_species = Lamna (Sphenodus) longidens | type_species_authority = Agassiz, 1843 }} thumb|right|upright|Sphenodus tooth from the oxfordian of Bel-Air, Hérault, France. '''''Sphenodus''''' is an extinct genus of shark. It is placed as a member of the extinct family Orthacodontidae, which is either considered to be a member of the extinct order Synechodontiformes,<ref name="Villalobos-Segura-2023">{{Cite journal |last1=Villalobos-Segura |first1=Eduardo |last2=Stumpf |first2=Sebastian |last3=Türtscher |first3=Julia |last4=Jambura |first4=Patrick L. |last5=Begat |first5=Arnaud |last6=López-Romero |first6=Faviel A. |last7=Fischer |first7=Jan |last8=Kriwet |first8=Jürgen |date=March 2023 |title=A Synoptic Review of the Cartilaginous Fishes (Chondrichthyes: Holocephali, Elasmobranchii) from the Upper Jurassic Konservat-Lagerstätten of Southern Germany: Taxonomy, Diversity, and Faunal Relationships |journal=Diversity |language=en |volume=15 |issue=3 |pages=386 |doi=10.3390/d15030386 |issn=1424-2818 |doi-access=free|pmid=36950327 |pmc=7614348 }}</ref> or the modern shark order Hexanchiformes.<ref name="CUSUMANO-2021">{{Cite journal |last1=CUSUMANO |first1=Antonio |last2=D'ARPA |first2=Carolina |last3=DUFFIN |first3=Christopher J. |date=2021 |title=Taxonomic revision of the shark Sphenodus in the Jurassic collections of the "Museo Geologico G.G. Gemmellaro" (Palermo, Sicily) |url=https://doi.org/10.4435/BSPI.2021.10 |journal=Bollettino della Società Paleontologica Italiana |pages=169–181 |doi=10.4435/BSPI.2021.10 |doi-broken-date=12 July 2025 |issn=0375-7633}}</ref>
== Species classification == 29 species have been described,<ref>{{Cite journal |last1=Kanno |first1=Shiori |last2=Nakajima |first2=Yasuhisa |last3=Hikida |first3=Yoshinori |last4=Sato |first4=Tamaki |date=2017-04-01 |title=Sphenodus (Chondrichthyes, Neoselachii) from the Upper Cretaceous in Nakagawa Town, Hokkaido, Japan |url=https://bioone.org/journals/paleontological-research/volume-21/issue-2/2016PR009/Sphenodus-Chondrichthyes-Neoselachii-from-the-Upper-Cretaceous-in-Nakagawa-Town/10.2517/2016PR009.full |journal=Paleontological Research |volume=21 |issue=2 |pages=122 |doi=10.2517/2016PR009 |s2cid=133054888 |issn=1342-8144|url-access=subscription }}</ref> though some of these are likely synonyms, which span from the Early Jurassic (Sinemurian) to Paleocene (Danian).<ref name="CUSUMANO-2021" /> Most species are only known from isolated teeth,<ref name="CUSUMANO-2021" /> though the species ''Sphenodus macer'' and ''Sphenodus nitidus'' from the Late Jurassic of Germany are known from skeletons. These suggest that it was relatively large, with a body length of {{Convert|2-3|m|ft}}, with a fusiform body with a single dorsal fin placed posteriorly without a fin spine.<ref name="Villalobos-Segura-2023" /> The teeth of ''Sphenodus'' consist of a single long, narrow central cusp, with much smaller lateral cusplets.<ref name="CUSUMANO-2021" /> Species of ''Sphenodus'' are thought to have been actively swimming predators, eating cephalopods.<ref name="Villalobos-Segura-2023" />
A 2025 study considered ''Sphenodus nitidus'' to be a synonym of ''S. macer,'' and suggested that ''Sphenodus'' should be considered a ''nomen dubium.'' This is due to a lack of diagnostic characters associated with original type specimen teeth used to define the genus, with ''S. macer'' assigned to the new genus ''Archaeogracilidens'' which was also placed as a member of Orthacodontidae within the Hexanchiformes.<ref>{{Cite journal |last1=Villalobos-Segura |first1=Eduardo |last2=Amadori |first2=Manuel |last3=Stumpf |first3=Sebastian |last4=Jambura |first4=Patrick L. |last5=Begat |first5=Arnaud |last6=Lopez-Romero |first6=Faviel A. |last7=Schweigert |first7=Günter |last8=Maxwell |first8=Erin E. |last9=Kriwet |first9=Jürgen |date=2025-12-31 |title=Articulated specimens provide new insights into the iconic Mesozoic shark genus Sphenodus |url=https://www.tandfonline.com/doi/full/10.1080/14772019.2025.2507014 |journal=Journal of Systematic Palaeontology |language=en |volume=23 |issue=1 |doi=10.1080/14772019.2025.2507014 |issn=1477-2019}}</ref>
==References== {{Reflist}} {{Taxonbar|from1=Q26996004}}
Category:Prehistoric shark genera Category:Fossil taxa described in 1843 Category:Elasmobranchii