| Sphenodus Temporal range: | |
|---|---|
 | |
| Skeleton of Sphenodus nitidus (SMNS 96844-7) from the Late Jurassic of Germany | |
 | |
| Tooth of Sphenodus nitidus | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Family: | † Orthacodontidae |
| Genus: | † Sphenodus Agassiz, 1843 |
| Type species | |
| Lamna (Sphenodus) longidens Agassiz, 1843 | |
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, [1] or the modern shark order Hexanchiformes. [2] 29 species have been described, [3] though some of these are likely synonyms, which span from the Early Jurassic (Sinemurian) to Paleocene (Danian). [2] Most species are only known from isolated teeth, [2] 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 2–3 metres (6.6–9.8 ft), with a fusiform body with a single dorsal fin placed posteriorly without a fin spine. [1] The teeth of Sphenodus consist of a single long, narrow central cusp, with much smaller lateral cusplets. [2] Species of Sphenodus are thought to have been actively swimming predators. [1]
A 2025 study considered Sphenodus nitidus to be a synonym of S. macer, and suggested that Sphenodus should be considered a nomen dubium 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. [4]