''Protospinax'' is an extinct genus of

cartilaginous fish Chondrichthyes (; ) is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fish'', which have skeleto ...

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� ...

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

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and

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. The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

, ''P. annectans'', was found in the Solnhofen limestones of southern

Bavaria Bavaria, officially the Free State of Bavaria, is a States of Germany, state in the southeast of Germany. With an area of , it is the list of German states by area, largest German state by land area, comprising approximately 1/5 of the total l ...

. Formerly known from only two specimens, further museum specimens of ''P. annectans'' were discovered at the

Museum of Comparative Zoology The Museum of Comparative Zoology (formally the Agassiz Museum of Comparative Zoology and often abbreviated to MCZ) is a zoology museum located on the grounds of Harvard University in Cambridge, Massachusetts. It is one of three natural-history r ...

Harvard University Harvard University is a Private university, private Ivy League research university in Cambridge, Massachusetts, United States. Founded in 1636 and named for its first benefactor, the History of the Puritans in North America, Puritan clergyma ...

in the 1990s, having been misidentified as '' Squatina'' and '' Heterodontus''. Five more species, all known only from isolated teeth, are also assigned to ''Protospinax''. ''Protospinax'' is a difficult taxon to accommodate in taxonomies. A 2023 study found it to be a squalomorph

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 the head. Modern sharks are classified within the ...

; one analysis placed it closest to angelsharks and sawsharks, but the authors concluded that its exact position within Squalomorphi is ultimately tentative due to a lack of unambiguous supporting traits. ''Protospinax'' was a relatively small shark, with the largest uncatalogued specimen of ''P. annectans'' measuring about long.

References

* Elasmobranchii Jurassic sharks Early Jurassic cartilaginous fish Middle Jurassic cartilaginous fish Late Jurassic cartilaginous fish Early Cretaceous cartilaginous fish Cretaceous sharks Solnhofen fauna Taxa named by Arthur Smith Woodward {{paleo-shark-stub