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Cretalamna is an extinct genus of otodontid mackerel shark that lived during the Late Cretaceous to possibly the Eocene. Cretalamna was an ecological generalist and was one of the most successful genera of all time, Cretalamna had a cosmopolitan distribution

Research History
Cretalamna was first described by Swiss naturalist Louis Agassiz using five teeth previously identified as the common smooth-hound and collected by English paleontologist Gideon Mantell from the Southerham Grey Pit near Lewes, East Sussex. In his 1835 publication Rapport sur les poissons fossiles découverts en Angleterre, he reidentified them as a new species of porbeagle shark under the taxon Lamna appendiculata. In 1843, Agassiz published Recherches sur les poissons fossiles, which reexamined Mantell's five teeth. Using them, eight additional teeth collected by Mantell, and twenty more teeth collected by various paleontologists in various locations (One tooth found by the 3rd Earl of Enniskillen from the Speeton Clay in Yorkshire; one tooth of the collection of a Strasbourg Museum from an unspecified location; one tooth of the collection of the Hancock Museum from the Marly Chalk near Cambridge; and six teeth of the collection of German paleontologist Heinrich Georg Bronn from chalk around Aachen), he described a species whose teeth had thick bulged roots, lateral cusplets, and extreme variability. Agassiz remarked that some of the examined teeth may be variable enough to belong to a separate species, but ultimately unified them under a new taxon Otodus appendiculatus. The species would later be found in 1958 by Soviet paleontologist Leonid Glickman to belong to a distinct new genus- Cretalamna.

Despite Agassiz's remarks on variability, his ultimatly broad interpretation of O. appendiculatus subsequently led the species to become a wastebasket taxon culminating to an interpretation of C. appendiculata as a variable cosmopolitan species with a 50 million year range. This changed when paleontologist Mikael Siversson found that the twenty-five syntypes actually represented a mix of at least six or more different species including three additional genera Dwardius, Cretoxyrhina, and Cretodus. To remedy the taxonomic issue, he redesignated one of the syntypes as the sole lectotype of C. appendiculata in 1999. In 2015, he led a study which revisited the taxonomic situation and established a renewed description of the species, which led to the erection of six additional Cretalamna species- C. catoxodon, C. deschutteri, C. ewelli, C. gertericorum, C. hattini, and C. sarcoporthea.

Before Siversson, other Cretalamna species have been described. Another species described by Agassiz under the taxon Otodus latus was demoted to a variation of C. appendiculata in 1908, promoted into a subspecies in 1977 by French paleontologist Jaques Herman, and finally elevated to the species level as Cretolamna lata by Herman and paleontologist Van Waes Hilde in 2012. In 1897, French paleontologist Fernand Priem described a single tooth from the Köpinge Sandstone in Scania, Sweden under the taxon Lamna borealis. This would be revised to  'Cretolamna borealis'  by Glickman in a 1980 paper. In 1902, German paleontologist Johannes Wanner described teeth from Egyptian Cretaceous deposits near the Dakhla Oasis and Farafra. He noted that the teeth are almost identical with that of the Otodus appendiculatus teeth, except that the Egyptian teeth also contained two clear pairs of lateral cusplets (a feature not seen in Otodus appendiculatus). Wanner concluded that the teeth were of a closely related new species and placed it under the taxon Otodus biauriculatus. In 1935, French Paleontologist Camille Arambourg described a new subspecies of C. biauriculata from teeth found in Moroccan phosphates under the taxon Lamna biauriculata maroccana, which was elevated into its own species in 1997. In 1972, French ichthyologist Henri Cappetta described teeth from Maastrichtian deposits near the Mentès well in Tahoua, Niger, which he assigned to the subspecies Lamna biauriculata nigeriana. This subspecies would also be elevated to its own species in 1991. In 1975, Cappetta and American paleontologist Gerard Case examined Cretalamna teeth described by Arambourg in 1952 from Danian deposits in Morocco and proposed that it represents a new subspecies of the type species and assigned it the taxon Cretolamna appendiculata arambourgi, which Siversson et al. (2015) elevated into its own species. In 2018, American paleontologists Jun Ebersole and Dana Ehret described a new species of Cretalamna from various teeth from the Eutaw Formation and Mooreville Chalk in Alabama, which they named C. bryanti.

Etymology
The genus Cretalamna is a portmanteau of creta, the Latin word for "chalk", prefixed to the genus Lamna, which is a romanization of the Ancient Greek λάμνα (lámna, meaning "kind of fierce shark"). When put together they mean "chalk-shark", which refers to chalk deposits from which the species' type specimens were found in. The type species name appendiculata is a feminine form of the Latin word appendiculātus (having an appendage), a reference to the thick bulged roots found in C. appendiculata teeth. The species name lata is derived from the feminine form of the Latin lātus (wide); a reference to the notably wide teeth of the species. The species name borealis is derived from the Latin boreālis (northern); this is a reference to its discovery from fossil deposits in Sweden, a boreal locality. The specific epithet of C. maroccana is a feminine form of the Latin word maroccānus (Moroccan), a reference to its type locality in Morocco. C. biauriculata's specific epithet is a portmanteau derived from the Latin prefix bi- (two) prefixed onto the Latin auriculātā (eared), together meaning "having two ears". This is a reference to the species' large lateral cusplets, which somewhat resemble a pair of ears. The species name nigeriana is derived from the country name Niger prefixed to the suffix -iana, a feminine variation of the Latin suffix -ānus (pertaining to), together meaning "pertaining to Niger". This is a reference to the species' type locality in Niger. The species name sarcoportheta is derived from the Ancient Greek σαρκός (sarkos, meaning "flesh") prefixed to the Ancient Greek πορθητής (porthitís, meaning "destroyer"), together meaning "destroyer of flesh". The species name catoxodon is derived from the Ancient Greek κατοξυς (katoxys, meaning "very sharp") prefixed to the Ancient Greek ὀδών (odon, meaning "tooth". Together they mean "very sharp tooth", referring to the unusually sharp cutting edges of some C. catoxodon teeth.

Six of the Cretalamna species have specific epithets that are named in honor of specific people, either for their contributions to the research of their associated species or for notable work they undertook. Of these six, five share a similar word structure that has a person's last name prefixed onto the Latin suffix -i (from). These species are C. arambourgi, which honors paleontologist Camille Arambourg for his discovery of the C. arambourgi type specimens and his contributions to North African paleontology; C. bryanti, which honors the Bryant family who helped enhance the reputation and missions of the University of Alabama, Alabama Museum of Natural History, and McWane Science Center through their commitment to education and support; C. deschutteri, which honors paleontologist Pieter De Scutter for his efforts to make Cretalamna teeth from a Bettrechies quarry available to Siversson et al. (2015) and for his work on Belgian Cenozoic sharks; C. ewelli, which honors paleontologist Keith Ewell who collected most of the C. ewelli type specimens in 2004; and C. hattini, which honors the late geologist Donald E. Hattin "for his work on the stratigraphy of the Niobrara Formation, western Kansas". The specific epithet of C. gertericorum is structured differently; it is derived from the names "Gert", "Eric", and the Latin suffix -orum (a masculine plural declension). The derived names "Gert" and "Eric" refer to fossil collectors Gert De Bie and Eric Collier, both of whom collected the majority of Cretalamna teeth examined in Siversson et al. (2015) that were from the Bettrechies quarry.

Spelling
The valid spelling of Cretalamna, specifically between it and  'Cretolamna', has been subject to controversy. Originally, Glickman described the genus with the intention of naming it as  'Cretolamna' , but during publication of the corresponding 1958 paper a typographical error occurred, with the print misspelling it as  'Cretalamna' . Glickman pointed out the spelling as an error and continued to use his intended spelling  'Cretolamna'  in later works. This spelling was universally adopted until 1999 when Siversson remarked that this violates ICZN Articles 32 and 33, reinstating  'Cretalamna'  as the valid spelling. Since then, the reinstatement of  'Cretalamna'  gained prominence and by the 2010s, was accepted by the majority of paleontologists. However, some paleontologists including Cappetta strongly opposed it. In an attempt to suppress the usage of  'Cretalamna' , Cappetta appealed to a representative of the ICZN, arguing that the original intentions of Glickman and the prevailing usage of  'Cretolamna'  prior to Siversson (1999) secures its priority. The ICZN, who reportedly were impressed by Cappetta's "spirit", subsequently erected Article 33.3.1 of the 2000 Edition of the Code in order to address this situation in the future, which states that "when an unjustified emendation is in prevailing usage and is attributed to the original author and date it is deemed to be a justified emendation". While Cappetta argued in a 2012 handbook that this new provision justifies the priority of  'Cretolamna'  due to the spelling's overwhelmingly prevailing usage prior to its replacement by Siversson in 1999, Siversson himself pointed out in a 2015 paper that the provision cannot be worked retroactively, and that the continued prevailing usage of  'Cretalamna'  since the provision's establishment ironically secures its priority rather than threaten it.  'Cretalamna'  currently remains as the most prevalent spelling and paleontologists have expressed the unlikeliness of a return to the usage of  'Cretolamna' .

Classification
Currently, at least fourteen valid species are attributed to Cretalamna, with additional poorly diagnosed or undescribed species that have yet to be so. However, due to the extreme variability between species,

For Cretalamna species that are of C. appendiculata type, Siversson et al. (2015) organized them into three groups- the C. appendiculata group containing C. appendiculata, C. sarcoportheta, and C. lata; the C. borealis group containing C. borealis, C. gertericorum, C. ewelli, and C. bryanti; and the C. hattini group containing C. hattini and C. deschutteri.

Description
Cretalamna was a medium-sized shark ranging between 2.5-4.2 m in estimated length.

Cretalamna fossils are very commons and have been found in all continents except Antarctica. However, the overwhelming majority of its fossil record consists of teeth, with very few skeletal examples known.

Dentition
As a genus consisting of at least fourteen different species, the teeth of Cretalamna are extremely variable. Unifying diagnostic features include one or two pairs of symmetrical lateral cusplets, bilobied roots, narrow tooth necks, and nonserrated cutting edges. Because of similar morphologies of the crown, diagnosing Cretalamna to the species level is typically based on the morphology of the root; it is remarked that Cretalamna teeth with even moderate abrasions at the root often renders them indeterminable at the species level.

Classification
Topology A: Lamnoidea hypothesis by Greenfield (2022)

Topology B: Non-Lamnoidea hypothesis by Sternes et al. (2022)