''Sphenodus'' is an extinct genus of shark. It is placed as a member of the extinct family
Orthacodontidae
Orthacodontidae is an extinct family of shark
Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to t ...
, which is either considered to be a member of the extinct order
Synechodontiformes
Synechodontiformes is an extinct order of prehistoric shark-like cartilaginous fish, known from the Permian to the Paleogene. They are considered to be members of Neoselachii, the group that contains modern sharks and rays.
Their placement ...
,
or the modern shark order
Hexanchiformes
The Hexanchiformes Help:IPA/English, /hɛkˈsæŋkɪfɔːrmiːz/ are a primitive Order (biology), order of sharks, numbering just five extant species in two Family (biology), families, Chlamydoselachidae and Cow shark, Hexanchidae. Chlamydoselach ...
.
29 species have been described, though some of these are likely synonyms, which span from the
Early Jurassic
The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic ...
(
Sinemurian
In the geologic timescale, the Sinemurian is an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic epoch (geology), Epoch or series (stratigraphy), Series. It spans the time between 199.5 ±0.3 annu ...
) to
Paleocene
The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...
(
Danian
The Danian is the oldest age or lowest stage of the Paleocene Epoch or Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian (and the end of the preceding Maastrichtian) is at the Cretac ...
).
Most species are only known from isolated teeth,
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 , with a
fusiform
Fusiform (from Latin ''fusus'' ‘spindle’) means having a spindle (textiles), spindle-like shape that is wide in the middle and tapers at both ends. It is similar to the lemon (geometry), lemon-shape, but often implies a focal broadening of a ...
body with a single dorsal fin placed posteriorly without a fin spine.
The teeth of ''Sphenodus'' consist of a single long, narrow central cusp, with much smaller lateral cusplets.
Species of ''Sphenodus'' are thought to have been actively swimming predators.
A 2025 study considered ''Sphenodus nitidus'' to be a synonym of ''S. macer,'' and suggested that ''Sphenodus'' should be considered a ''
nomen dubium
In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application.
Zoology
In case of a ''nomen dubium,'' it may be impossible to determine whether a ...
'' due to a lack of diagnostic characters associated with original
type specimen
In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...
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.
References
{{taxonbar, from1=Q26996004
Prehistoric shark genera
Fossil taxa described in 1843