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, such as '' Otodus angustidens'', '' Otodus chubutensis'', and ''Otodus megalodon''.

Taxonomy

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 ultimately 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 Belgian 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. biauriculatas 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 (, meaning "flesh") prefixed to the Ancient Greek (, meaning "destroyer"), together meaning "destroyer of flesh". The species name ''catoxodon'' is derived from the Ancient Greek (, meaning "very sharp") prefixed to the Ancient Greek (, 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' ''.

Description

''Cretalamna'' was a medium to large-sized shark. Based on vertebral comparisons with various extant lamniforms and ''Cretoxyrhina'', a 2007 study by Kenshu Shimada estimated a total length of for the most complete skeleton of a large individual (LACM 128126; ''C. hattini'' holotype). Shimada previously discovered that the total length of lamniform sharks is positively correlated with the size of their teeth in a reasonably linear relationship; thus, Shimada (2007)'s estimates enabled size estimations for ''Cretalamna'' based on teeth alone. Subsequently, in 2019, the teeth of ''C. appendiculata'' from Himedo Park, Kugushima and Wadanohana which are larger than those in LACM 128126 yielded maximum length estimates of up to , and , respectively. In 2020, Shimada and colleagues estimated the maximum possible length of ''C. borealis'' up to based on an upper jaw tooth specimen (LO 11350t) from Åsen locality.

Body

The body plan of ''Cretalamna'' is almost completely known, informed by near-complete fossil impressions with soft tissue preserving the shark's outline from the Hjoula lagerstätte in Lebanon as documented by Pfiel (2021) and Greenfield (2022). It was most similar to the porbeagle and salmon sharks in build, with a compact fusiform body, large pectoral and first dorsal fins and tail, and small second dorsal, pelvic, and anal fins. The first dorsal fin was positioned directly above the pectoral fins unlike its analog species, where the first dorsal fin is usually positioned behind it. The tail fin was semi-lunate, similar to the whale shark. Such a body plan is indicative of an active fast-swimming pelagic shark likely partially warm-blooded through regional endothermy. In their 2024 study's appendix, Sternes and colleagues questioned this particular specimen's authenticity and anatomical parts which can only be speculated by photographs and its uncertain catalog status did not allow the reproducibility of the proportions suggested by Greenfield (2022).

Dentition

''Cretalamna'' teeth are distinguished by a broad triangular cusp and two lateral cusplets. The cutting edges of the teeth are razor-like, while the sides have a smooth surface. Teeth symmetry is variable; some have exact bilateral symmetry whereas others have high asymmetry. Adjacent teeth do not overlap.

The exact dentition of ''Cretalamna'' is uncertain due to poor fossil representation. Traditionally, most reconstructions of its dentition were constructed from individual shed teeth. Based on a specimen of ''C. hattini'' (LACM 128126), the dentition of the shark follows a lamnoid pattern with at least fifteen upper tooth rows and eight lower tooth rows on each side of the jaw. The upper tooth rows contain, from front to back: two symphysial, two anterior, one intermediate, and ten lateral tooth rows. The lower tooth rows contain: two anterior, one intermediate, and five lateral tooth rows. This is given in the dental formula , constructed in a 2007 study of LACM 128126 by paleontologist Kenshu Shimada. It is possible that ''Cretalamna'' contained more than two symphysial tooth rows, as the related ''Cretoxyrhina mantelli'' possessed four upper symphysial tooth rows.

Jaw

In ''C. hattini'', the upper and lower jaws are similar to that of ''Cretoxyrhina mantelli''. The jaws also resemble those of modern alopiids (thresher sharks) and lamnids. Limited fossil evidence suggests that the upper jaws extended over the lower jaws, giving ''Cretalamna'' a subterminal mouth.

Paleoecology

Distribution

''Cretalamna'' was a widespread genus found in North Africa (Morocco), the Near East (Jordan), West Africa (Mali), North America both on the East Coast and in the Midwest and Central America (Tonosí, Panama). Deposits in Morocco are usually Eocene in age; deposits in Jordan are of Cretaceous and Eocene in age; most deposits in the U.S. are of Cretaceous and Paleocene age; and deposits in Mali are of Cretaceous (Maastrichtian) age. ''C. maroccana'' is more prevalent in Morocco and Jordan, while ''C. appendiculata'' is more prevalent in the United States. Both species overlapped at one point in time.

Habitat

Fossil evidence of ''Cretalamna'' is found in deposits representing a diverse set of marine environments, indicating that it was able to adapt to a wide range of habitats. This may have attributed to its ability to exist through a long temporal range. The fusiform body of ''Cretalamna'' suggests it was a pelagic shark.

The Cretaceous waters inhabited by ''Cretalamna'' were also home to a diverse range of cartilaginous fishes, bony fishes, turtles, squamates, plesiosaurs, pterosaurs, birds, and even some non-avian dinosaurs.

Diet

The tooth morphology of ''Cretalamna'' implies that it was a generalist. It was a predator and preyed upon large bony fish, turtles, mosasaurs, squids, and other sharks. For example, multiple teeth of ''C. appendiculata'' have been found around elasmosaurid '' Futabasaurus'', suggesting it predated or scavenged that elasmosaur. Some tooth specimens of ''Cretalamna'' exhibit heavy wear—likely the result of drastic diet changes.

Extinction

A possible factor to the extinction of ''Cretalamna'' is increased competition with newer generalist sharks during the Cenozoic. It is widely believed that ''Otodus'' (and thus ''Carcharocles'') is derived from ''Cretalamna'' due to its strong similarity to certain species within the genus.

See also

* Cretaceous sharks
* Prehistoric fish
* ''Squalicorax''

Notes

References

{{Taxonbar, from=Q5184739

Otodontidae
Cretaceous sharks
Paleocene sharks
Eocene sharks
Eocene genus extinctions
Camarillas Formation
Prehistoric fish of North America
Demopolis Chalk
Mooreville Chalk
Enigmatic fish taxa
Prehistoric shark genera
Fossil taxa described in 1958
Fossils of Mali
Albian genus first appearances