''Cretodus'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus of large

mackerel sharks The Lamniformes (, from Greek ''lamna'' "fish of prey") are an order of sharks commonly known as mackerel sharks (which may also refer specifically to the family Lamnidae). It includes some of the most familiar species of sharks, such as the gre ...

belonging to the proposed family

Pseudoscapanorhynchidae Pseudoscapanorhynchidae is a family of extinct mackerel sharks that lived during the Cretaceous and potentially the Paleogene. It currently includes '' Cretodus'', ''Eoptolamna'', '' Leptostyrax'', ''Protolamna'', ''Pseudoscapanorhynchus'', and p ...

. ''Cretodus'' lived during the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

, ranging from the

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...

Cicimurri, D. J. (2001). "Fossil selachians from the Belle Fourche Shale (Cretaceous, Cenomanian), Black Hills region of South Dakota and Wyoming." ''Mountain Geologist,'' 38:181-192. to the

Coniacian The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series and spans the time between 89.8 ± 1 Ma and 86.3 ± 0.7 Ma (million years ago). The Coniacian is preceded by t ...

Hamm S.A. & Cicimurri D. J. (2011). "Early Coniacian (Late Cretaceous) selachian fauna from the basal Atco Formation, lower Austin Group, north central Texas." ''Paludicola'', 8(3): 107-127. (approximately 100 to 89 million years ago). The genus is well-known from

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

deposited in the

Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea that split the continent of North America into two landmasses. The ancient sea, ...

(

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

), and from the Late Cretaceous of

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

, and possibly

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...

. ''Cretodus'' is primarily represented in the

fossil record A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

by isolated

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

and

vertebral The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordates ...

centra, though a couple of associated dentitions and vertebral columns have been found.

Description

Prior to 2017, ''Cretodus'' was mainly known from isolated teeth.Amalfitano, J., F. M. Dalla Vecchia, L. Giusberti, E. Fornaciari, V. Luciani, and G. Roghi (2017). "Direct evidence of trophic interaction between a large lamniform shark, ''Cretodus'' sp., and a marine turtle from the Cretaceous of northeastern Italy." Palaeogeography, Palaeoclimatology, Palaeoecology 469:104–121. doi: 10.1016/j.palaeo.2016.12.044 The discovery of a virtually complete

skeleton A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

suggests the genus possessed a body similar in form to the modern

tiger shark The tiger shark (''Galeocerdo cuvier'') is a species of requiem shark and the last extant member of the family Galeocerdonidae. It is a large macropredator, capable of attaining a length over . Populations are found in many tropical and tempera ...

, with a wide head that was equipped with powerful jaws, and a stout body. The

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

of ''Cretodus''' placoid scales and vertebral centra suggest a moderate swimming speed, less than that of the fast-cruising contemporaneous macropredatory shark, ''

Cretoxyrhina ''Cretoxyrhina'' (; meaning 'Cretaceous sharp-nose') is an extinct genus of large mackerel shark that lived about 107 to 73 million years ago during the late Albian to late Campanian of the Late Cretaceous. The type species, ''C. mantelli'', is m ...

''. Size estimation is only reasonable for the few associated partial skeletons known. Shimada & Everhart (2019) reported an approximate total length of for the associated specimen of ''C. houghtonorum'' from

Kansas Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the ...

which probably died at 22 years of age; they also suggested that the maximum total length of ''C. houghtonorum'' would have been . Amalfitano ''et al.'' (2022) reported an estimated total length of for a nearly complete specimen of ''C. crassidens'' from

Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...

which probably died at 23 years of age; they also used a growth model to estimate the maximum total length for ''C. crassidens'' at .

Dentition

''Cretodus'' teeth have lateral cusplets that are much smaller than the main cusp and well-separated from it, but connected by enamel on the labial face. The enamel surface is smooth, except near the base of the crown, where it forms vertical striae or costulae (grooves and ridges), a feature more prominent on the lingual face. The root is bilobate and has a massive shelf-like lingual root protuberance which diminishes in size in posterior positions.Welton, B. J., and R. F. Farish (1993). "The Collector’s Guide to Fossil Sharks and Rays from the Cretaceous of Texas." Before Time, Lewisville, Texas, 204 pp.

Growth

It is estimated that ''C. houghtonorum'' was about long at birth, became sexually mature at 10 to 15 years of age, and reached its maximum lifespan at 51 to 55 years of age. ''C. crassidens'' was about long at birth, became sexually mature at 12 to 17 years of age, and reached its maximum life span at 64 years of age.

Paleoecology

''Cretodus'' predated on large prey, and is suggested to have specialized in marine turtles, based on inferred stomach contents (a chelonioid turtle) of a specimen of ''C''. ''crassidens'' found in Italy''.'' A predator-prey relationship has also been inferred between ''C. houghtonorum'' and

hybodont Hybodontiformes, commonly called hybodonts, are an extinct group of shark-like chondrichthyans, which existed from the late Devonian to the Late Cretaceous. They form the group of Elasmobranchii closest to neoselachians, the clade of modern shark ...

sharks based on stomach contents. The distribution of fossils of ''C. crassidens'' suggests a largely cosmopolitan distribution and a preference for offshore areas in contrast with other species in the genus (e.g. ''C. houghtonorum''), which preferred shallow water. Within the Western Interior Seaway, ''Cretodus'' lived among a number of other genera of shark including ''Cretoxyrhina,

Squalicorax ''Squalicorax'', commonly known as the crow shark, is a genus of extinct lamniform shark known to have lived during the Cretaceous period. The genus had a global distribution in the Late Cretaceous epoch. Multiple species within this genus are c ...

'', '' Ptychodus,

Cretalamna ''Cretalamna'' is a genus of extinct otodontid shark that lived from the latest Early Cretaceous to Eocene epoch (about 103 to 46 million years ago). It is considered by many to be the ancestor of the largest sharks to have ever lived, ''Otodus ...

Scapanorhynchus ''Scapanorhynchus'' (from el, σκάφιου , 'shovel' and el, ῥύγχος 'snout') is an extinct genus of shark that lived from the early Cretaceous until possibly the Miocene if ''S. subulatus'' is a mitsukurinid and not a sand shark.Capet ...

,'' and hybodont sharks. In order to coexist, these sharks likely practiced

resource partitioning In ecology, niche differentiation (also known as niche segregation, niche separation and niche partitioning) refers to the process by which competing species use the environment differently in a way that helps them to coexist. The competitive excl ...

, by occupying different regions (e.g. nearshore v.s. offshore) or specializing in different prey items.

Species

Shimada & Everhart (2019) attributed the following species to the genus, asserting they were

chronospecies A chronospecies is a species derived from a anagenesis, sequential development pattern that involves continual and uniform changes from an extinct ancestral form on an evolutionary scale. The sequence of alterations eventually produces a populatio ...

belonging to three grades of crown broadness. * ''Cretodus longiplicatus'' * ''Cretodus semiplicatus'' * ''Cretodus gigantea'' * ''Cretodus houghtonorum'' * ''Cretodus crassidens''

References

{{Taxonbar, from=Q104848348 Late Cretaceous fish of North America Lamniformes Prehistoric shark genera Turonian life Cretaceous sharks Fossils of Uzbekistan Bissekty Formation