| Cretalamna | |
|---|---|
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| Jaws and teeth of theC. hattiniholotype (LACM 128126) from theNiobrara Formation ofKansas | |
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| Speculative skeletal reconstruction | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Division: | Selachii |
| Order: | Lamniformes |
| Family: | †Otodontidae |
| Genus: | †Cretalamna Glükman, 1958 |
| Type species | |
| †Lamna appendiculata Agassiz, 1835 | |
| Species | |
List of species
| |
| Synonyms[1][6][7][8][9] | |
List of synonyms
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Cretalamna is a genus ofextinctotodontid shark that lived from the latestEarly Cretaceous toEocene 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 asOtodus angustidens,Otodus chubutensis, andOtodus megalodon.
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Cretalamna was first described bySwiss naturalistLouis Agassiz using five teeth previously identified as thecommon smooth-hound and collected by English paleontologistGideon Mantell from theSoutherham Grey Pit nearLewes,East Sussex. In his 1835 publicationRapport sur les poissons fossiles découverts en Angleterre, he reidentified them as a new species ofporbeagle shark under the taxonLamna appendiculata.[9] In 1843, Agassiz publishedRecherches 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 the3rd Earl of Enniskillen from theSpeeton Clay inYorkshire; one tooth of the collection of a Strasbourg Museum from an unspecified location; one tooth of the collection of theHancock Museum from theMarly Chalk nearCambridge; and six teeth of the collection ofGerman paleontologistHeinrich Georg Bronn from chalk aroundAachen), 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 taxonOtodus appendiculatus.[10] The species would later be found in 1958 by Soviet paleontologist Leonid Glickman to belong to a distinct new genus-Cretalamna.[11]
Despite Agassiz's remarks on variability,[10] his ultimately broad interpretation ofO. appendiculatus subsequently led the species to become awastebasket taxon culminating to an interpretation ofC. appendiculata as a variablecosmopolitan 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 generaDwardius,Cretoxyrhina, andCretodus. To remedy the taxonomic issue, he redesignated one of the syntypes as the solelectotype ofC. appendiculata in 1999.[1][12] 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 additionalCretalamna species-C. catoxodon,C. deschutteri,C. ewelli,C. gertericorum,C. hattini, andC. sarcoporthea.[1]
Before Siversson, otherCretalamna species have been described. Another species described by Agassiz under the taxonOtodus latus was demoted to a variation ofC. appendiculata in 1908,[13] promoted into a subspecies in 1977 by Belgian paleontologist Jaques Herman,[14] and finally elevated to the species level asCretolamna lata by Herman and paleontologist Van Waes Hilde in 2012.[15] In 1897, French paleontologist Fernand Priem described a single tooth from the Köpinge Sandstone inScania,Sweden under the taxonLamna borealis. This would be revised to 'Cretolamna borealis' by Glickman in a 1980 paper.[1] In 1902, German paleontologist Johannes Wanner described teeth fromEgyptian Cretaceous deposits near theDakhla Oasis andFarafra. He noted that the teeth are almost identical with that of theOtodus appendiculatus teeth, except that the Egyptian teeth also contained two clear pairs of lateral cusplets (a feature not seen inOtodus appendiculatus). Wanner concluded that the teeth were of a closely related new species and placed it under the taxonOtodus biauriculatus.[16] In 1935, French Paleontologist Camille Arambourg described a new subspecies ofC. biauriculata from teeth found in Moroccan phosphates under the taxonLamna biauriculata maroccana,[17] which was elevated into its own species in 1997.[18] In 1972,FrenchichthyologistHenri Cappetta described teeth from Maastrichtian deposits near the Mentès well inTahoua,Niger, which he assigned to the subspeciesLamna biauriculata nigeriana.[19] This subspecies would also be elevated to its own species in 1991.[20] In 1975, Cappetta and American paleontologist Gerard Case examinedCretalamna 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 taxonCretolamna appendiculata arambourgi,[21] which Siverssonet al. (2015) elevated into its own species.[1] In 2018, American paleontologists Jun Ebersole and Dana Ehret described a new species ofCretalamna from various teeth from theEutaw Formation andMooreville Chalk inAlabama, which they namedC. bryanti.[22]
The genusCretalamna is a portmanteau ofcreta, the Latin word for "chalk", prefixed to the genusLamna, which is aromanization 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.[11] The type species nameappendiculata is a feminine form of the Latin wordappendiculātus (having an appendage), a reference to the thick bulged roots found inC. appendiculata teeth.[10] The species namelata is derived from the feminine form of the Latinlātus (wide); a reference to the notably wide teeth of the species.[10] The species nameborealis is derived from the Latin boreālis (northern); this is a reference to its discovery from fossil deposits in Sweden, a boreal locality.[1] The specific epithet ofC. maroccana is a feminine form of the Latin wordmaroccānus (Moroccan), a reference to its type locality in Morocco.[23]C. biauriculata's specific epithet is a portmanteau derived from the Latin prefixbi- (two) prefixed onto the Latinauriculātā (eared), together meaning "having two ears". This is a reference to the species' large lateral cusplets, which somewhat resemble a pair of ears.[16] The species namenigeriana 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.[19] The species namesarcoportheta is derived from the Ancient Greekσαρκός (sarkos, meaning "flesh") prefixed to the Ancient Greekπορθητής (porthitís, meaning "destroyer"), together meaning "destroyer of flesh". The species namecatoxodon is derived from the Ancient Greekκατοξυς (katoxys, meaning "very sharp") prefixed to the Ancient Greekὀδών (odon, meaning "tooth". Together they mean "very sharp tooth", referring to the unusually sharp cutting edges of someC. catoxodon teeth.[1]
Six of theCretalamna 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 areC. arambourgi, which honors paleontologist Camille Arambourg for his discovery of theC. arambourgi type specimens and his contributions to North African paleontology;[21]C. bryanti, which honors theBryant family who helped enhance the reputation and missions of theUniversity of Alabama,Alabama Museum of Natural History, andMcWane Science Center through their commitment to education and support;[22]C. deschutteri, which honors paleontologist Pieter De Scutter for his efforts to makeCretalamna teeth from aBettrechies quarry available to Siverssonet al. (2015) and for his work on Belgian Cenozoic sharks;C. ewelli, which honors paleontologist Keith Ewell who collected most of theC. ewelli type specimens in 2004; andC. hattini, which honors the late geologist Donald E. Hattin "for his work on the stratigraphy of the Niobrara Formation, western Kansas". The specific epithet ofC. 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 ofCretalamna teeth examined in Siverssonet al. (2015) that were from the Bettrechies quarry.[1]
The valid spelling ofCretalamna, 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 atypographical 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.[17] This spelling was universally adopted until 1999 when Siversson remarked that this violates ICZN Articles 32 and 33, reinstating 'Cretalamna' as the valid spelling.[12] Since then, the reinstatement of 'Cretalamna' gained prominence and by the 2010s, was accepted by the majority of paleontologists.[1] However, some paleontologists including Cappetta strongly opposed it.[1][17] 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,[17] 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.[1] 'Cretalamna' currently remains as the most prevalent spelling and paleontologists have expressed the unlikeliness of a return to the usage of 'Cretolamna'.[17]
Cretalamna was a medium to large-sized shark. Based on vertebral comparisons with various extantlamniforms andCretoxyrhina, a 2007 study by Kenshu Shimada estimated a total length of 2.3–3.0 metres (8–10 ft) for the most complete skeleton of a large individual (LACM 128126;C. hattini holotype[1]).[24] 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 forCretalamna based on teeth alone.[25][26] Subsequently, in 2019, the teeth ofC. appendiculata from Himedo Park, Kugushima and Wadanohana which are larger than those in LACM 128126 yielded maximum length estimates of up to 3.4 metres (11 ft), 4.5 metres (15 ft) and 5 meters (16 ft), respectively.[26] In 2020, Shimada and colleagues estimated the maximum possible length ofC. borealis up to 3.5 meters (11 ft) based on an upper jaw tooth specimen (LO 11350t) from Åsen locality.[27][1]
The body plan ofCretalamna is almost completely known, informed by near-complete fossil impressions with soft tissue preserving the shark's outline from theHjoulalagerstätte inLebanon as documented by Pfiel (2021) and Greenfield (2022).[28] It was most similar to theporbeagle andsalmon 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.[28] The tail fin was semi-lunate,[28] similar to thewhale shark.[29] Such a body plan is indicative of an active fast-swimming pelagic shark likely partially warm-blooded throughregional endothermy.[28][30] 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).[31]
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.[24]
The exactdentition ofCretalamna is uncertain due to poor fossil representation. Traditionally, most reconstructions of its dentition were constructed from individual shed teeth.[1] Based on a specimen ofC. 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 formulaS2?.A2.I1.L10(+?)s?.a2.i1.l4, constructed in a 2007 study of LACM 128126 by paleontologist Kenshu Shimada. It is possible thatCretalamna contained more than two symphysial tooth rows, as the relatedCretoxyrhina mantelli possessed four upper symphysial tooth rows.[24]
InC. hattini, the upper and lower jaws are similar to that ofCretoxyrhina mantelli. The jaws also resemble those of modernalopiids (thresher sharks) andlamnids. Limited fossil evidence suggests that the upper jaws extended over the lower jaws, givingCretalamna a subterminal mouth.[24]
Cretalamna was a widespread genus found in North Africa (Morocco), the Near East (Jordan),[32] West Africa (Mali),[33] North America both on the East Coast and in theMidwest and Central America (Tonosí,Panama).[34] 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;[35] and deposits in Mali are of Cretaceous (Maastrichtian) age.[33]C. maroccana is more prevalent in Morocco and Jordan, whileC. appendiculata is more prevalent in the United States. Both species overlapped at one point in time.
Fossil evidence ofCretalamna 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.[24] The fusiform body ofCretalamna suggests it was apelagic shark.[36]
The Cretaceous waters inhabited byCretalamna were also home to a diverse range of cartilaginous fishes, bony fishes, turtles, squamates, plesiosaurs, pterosaurs, birds, and even some non-avian dinosaurs.[24]
The tooth morphology ofCretalamna implies that it was a generalist.[24] It was apredator and preyed upon large bony fish,turtles,mosasaurs, squids, and other sharks.[37] For example, multiple teeth ofC. appendiculata have been found aroundelasmosauridFutabasaurus, suggesting it predated or scavenged that elasmosaur.[25] Some tooth specimens ofCretalamna exhibit heavy wear—likely the result of drastic diet changes.[1]
A possible factor to the extinction ofCretalamna is increased competition with newer generalist sharks during the Cenozoic.[24] It is widely believed thatOtodus (and thusCarcharocles) is derived fromCretalamna due to its strong similarity to certain species within the genus.[22]