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Leviathanochelys

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Extinct genus of turtle

Leviathanochelys Temporal range: Campanian PreꞒ Ꞓ O S D C P T J K Pg N

Type material ofLeviathanochelys''
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Testudines
Suborder:	Cryptodira
Superfamily:	Chelonioidea
Genus:	†Leviathanochelys Castillo-Visaet al., 2022
Species:	†L. aenigmatica
Binomial name
†Leviathanochelys aenigmatica Castillo-Visaet al., 2022

Leviathanochelys is an extinct genus of giantsea turtle from theMiddle Campanian of northernSpain. Although only known from the rear end of thecarapace and the connectingpubic bones, these elements clearly show that they belonged to a turtle of great size, comparable in dimensions to the giantArchelon andProtostega from theWestern Interior Seaway of theUSA. This makesLeviathanochelys the first giant sea turtle known from Europe and one of the largest known turtles of all time. This great size was evolved independently from the Americanprotostegid turtles and was likely an adaptation to the conditions of the Cretaceous oceans covering much of Europe. Being classified in the superfamilyChelonioidea,Leviathanochelys is likely more closely related to modern sea turtles (familiesDermochelyidae andCheloniidae) than the protostegids, which are thought to be morebasal and have a more uncertain relationship to modern sea turtles.Leviathanochelys is thought to have been a pelagic animal. The genus contains a single species,Leviathanochelys aenigmatica.

Discovery and naming

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Map of the Cal Torrades Locality and stratigraphy of the Perles formation

The remains ofLeviathanochelys were discovered in 2016 by a hiker^[1] at the Cal Torrades locality in the SpanishPyrenees, which corresponds with the lowerPerles Formation. Within this locality, the fossil material was discovered approximately 20 cm (7.9 in) above the sandstone that forms the base of the locality, within a layer of greymarls. The turtle was named based on theholotype specimen MCD9884, which represents the posterior end of the animal's shell including the 5th to 8thneural andcostal plates, an almost unidentifiable bone thought to be a vertebra and much of thepelvic girdle including bothpubis,ischia andilia.^[2]

The nameLeviathanochelys is an allusion to the biblicalleviathan, a massive marine beast that was chosen due to the turtle's great size. The second part of the genus name is chelys, a Latinized version of the Greek χέλυς (khélūs) for turtle. Thespecies name aenigmatica is likewise Latinized Greek, deriving from αἴνιγμα (aínigma) meaning enigma, due to the anatomy of the fossil material.^[2]

Description

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The carapace ofLeviathanochelys is only known from the 5th neural and costal plates onward but clearly shows a smooth, slightly convex surface. The preserved plates show no marks left byscutes and there appear to be no ridges or depressions on the plates either. The costal plates, which are the large plates of the carapace located on either side of the spine, are wider than they are long and subrectangular in shape. The neural plates which run down the center of the carapace are only poorly preserved, with the first and last of the present bones (corresponding to the 5th and 8th plate in an intact shell) being incomplete. The 6th is the largest of the neural series and shaped like an octagon, while the 7th is reduced towards its end and hexagonal.^[2]

The pelvis is flat and H-shaped, clearly setting it apart from sea turtles likeToxochelys, with both pubes being fused to one another. The front sides of the pelvis bear a unique accessory process that, based on the structures surface, likely connected to musculature. This trait is exclusive toLeviathanochelys and not observed in any other sea turtle, extant or extinct. Generally, several important muscles attach to the pelvis in sea turtles, with its anterior side specifically connecting to theRectus abdominis muscle and the musculus puboischiofemoralis. While the former stabilizes the pubis and aids in breathing while the later is tied to the movement of the hindlimbs. Castillo-Visa and colleagues argue that the position of the accessory process and the lack of muscle scars make it unlikely that it was connected to mobility and instead propose that aided in respiration.^[2]

Leviathanochelys has been noted for its massive size, with the pelvis alone reaching a width of 88.9 cm (35.0 in), which is larger than the same bones in the giantArchelon with a width of 81 cm (32 in). The length of the pelvis is likewise enormous. With a pelvic length of 39.5 cm (15.6 in) it is over 100% longer than that ofProtostega (18 cm (7.1 in)) and only slightly shorter than that ofArchelon (46 cm (18 in)). Although there is no direct way of calculating total body length from the dimensions of the pelvis alone, these measurements indicate thatLeviathanochelys could reach similar proportions as these giantprotostegids, with the authors suggesting a potential body length of 3.74 m (12.3 ft).^[2]

Phylogeny

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The closest relative ofLeviathanochelys wasAllopleuron

Phylogenetic analysis recoveredLeviathanochelys as a basal member of the sea turtle superfamilyChelonioidea, specifically a sister taxon of the MaastrichtianAllopleuron hoffmanni. However Castillo-Visa and colleagues note that this grouping is only supported by a single commonsynapomorphy, the fact that the pelvis is connected to the shell not through a bony suture but through ligaments. This causes further problems, as this is the state for a large number of turtles and subsequently highlyplesiomorphic. The placement of both these taxa within Chelonioidea is however supported by several other traits.^[2]

Chelonioidea

Dermochelydae

	†Eosphargis breineri

	Leatherback sea turtle (Dermochelys coriacea)

†Nichollsemys baieri

	†Leviathanochelys aenigmatica

	†Allopleuron hoffmanni

†Procolpochelys charlestonensis

†Argillochelys cuneiceps

	†Eochelone brabantica

	†Puppigerus camperi

Ctenochelydae

	†Cabindachelys landanensis

	†Ctenochelys sp.

	†Peritresius martini

Cheloniidae

Australian flatback sea turtle (Natator depressus)

Hawksbill sea turtle (Eretmochelys imbricata)

Green sea turtle (Chelonia mydas)

Kemp's ridley sea turtle (Lepidochelys kempii)

	Loggerhead sea turtle (Caretta caretta)

	Olive ridley sea turtle (Lepidochelys olivacea)

Paleobiology

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Aside from the nature of the sedimentsLeviathanochelys has been found in, its marine lifestyle is further confirmed by thehistology of the costal plates. In this point,Leviathanochelys again bears resemblance toArchelon, indicating that both shared a similar lifestyle. In this case, both were likely pelagic open-water animals. The interpretation that this taxon's unique accessory process on the pelvis is connected to respiration would give additional credence to this lifestyle.^[2]

References

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^"Descubiertos en el Pirineo restos de hace 83 millones de años de la mayor tortuga marina de Europa".El Mundo (in Spanish). November 17, 2022. RetrievedNovember 17, 2022.
^^a ^b ^c ^d ^e ^f ^gCastillo-Visa, O.; Luján, À.H.; Galobart, À.; Sellés, A. (2022)."A gigantic bizarre marine turtle (Testudines: Chelonioidea) from the Middle Campanian (Late Cretaceous) of South-western Europe".Sci Rep.12 (1): 18322.Bibcode:2022NatSR..1218322C.doi:10.1038/s41598-022-22619-w.PMC 9671902.PMID 36396968.

Testudines

Kingdom:Animalia
Phylum:Chordata
Class:Reptilia
Clade:Diapsida
Order:Testudines

Genus

Chelonioidea
(Sea turtles)

Cheloniidae	†Allopleuron Caretta †Carolinochelys Chelonia †Eochelone Eretmochelys †Gigantatypus †Glarichelys †Itilochelys Lepidochelys †Mexichelys †Miocaretta Natator †Pacifichelys †Syllomus †Tasbacka
Dermochelyidae	†Arabemys †Corsochelys †Cosmochelys Dermochelys †Eosphargis †Mesodermochelys †Psephophorus
	†Euclastes †Peritresius †Procolpochelys †Protosphargis †Puppigerus

Kinosternoidea

Dermatemydidae	Dermatemys
Kinosternidae	Claudius †Hoplochelys Kinosternon Staurotypus Sternotherus

Testudinoidea

Emydidae	†Acherontemys Chrysemys Clemmys Deirochelys Emys Actinemys Emydoidea Glyptemys Graptemys Malaclemys Pseudemys Terrapene Trachemys †Wilburemys
Geoemydidae	Batagur †Banhxeochelys Cuora Cyclemys Geoclemys Geoemyda Hardella Heosemys Leucocephalon Malayemys Mauremys Melanochelys Morenia Notochelys Orlitia Pangshura Rhinoclemmys Sacalia Siebenrockiella Vijayachelys
Platysternidae	Platysternon
Testudinidae	Aldabrachelys Astrochelys Centrochelys Chelonoidis Chersina Cylindraspis †Cymatholcus †Floridemys Geochelone Gopherus †Hadrianus †Hesperotestudo Homopus Indotestudo Kinixys Malacochersus Manouria †Megalochelys †Oligopherus Psammobates Pyxis †Solitudo Stigmochelys †Stylemys Testudo

Trionychia

Carettochelyidae	†Allaeochelys †Anosteira Carettochelys
Trionychidae	Amyda Apalone †Axestemys Chitra Cyclanorbis Cycloderma †Drazinderetes Dogania †Gilmoremys †Hutchemys †Khunnuchelys Lissemys Nilssonia Palea †Palaeoamyda Pelochelys Pelodiscus Rafetus Trionyx
	†Basilochelys †Sinaspideretes

Chelydridae	Chelydra †Chelydrops †Chelydropsis †Emarginachelys †Macrocephalochelys Macrochelys †Planiplastron †Protochelydra
†Nanhsiungchelyidae	†Anomalochelys †Basilemys †Jiangxichelys
†Protostegidae	†Alienochelys †Archelon †Atlantochelys †Bouliachelys †Calcarichelys †Cratochelone †Desmatochelys †Iserosaurus †Notochelone †Ocepechelon †Pneumatoarthrus †Protostega †Rhinochelys †Santanachelys †Terlinguachelys
	†Adocus †Argillochelys †Bashuchelys †Ctenochelys †Prionochelys †Toxochelys

Pleurodira

†Araripemydidae	†Araripemys
†Bothremydidae	†Araiochelys †Arenila †Azabbaremys †Bothremys †Cearachelys †Chedighaii †Chupacabrachelys †Eotaphrosphys †Foxemys †Galianemys †Ilatardia †Inaechelys †Itapecuruemys †Jainemys †Kinkonychelys †Kurmademys †Labrostochelys †Nigeremys †Phosphatochelys †Polysternon †Puentemys †Rosasia †Rhothonemys †Sankuchemys †Taphrosphys †Ummulisani †Zolhafah
Chelidae	Acanthochelys Chelodina Chelus Elseya Elusor Emydura Hydromedusa †Lomalatachelys Mesoclemmys Myuchelys Phrynops Platemys †Prochelidella Pseudemydura Rheodytes Rhinemys †Yaminuechelys
Pelomedusidae	Pelomedusa Pelusios
Podocnemididae	†Albertwoodemys †Bauruemys †Brontochelys †Caninemys †Carbonemys †Cerrejonemys †Cordichelys Erymnochelys †Lapparentemys †Latentemys Peltocephalus Podocnemis †Stupendemys
†Sahonachelyidae	†Sahonachelys †Sokatra

	†Caribemys †Caririemys †Tacuarembemys

Phylogenetic arrangement of turtles based onTurtles of the World 2017 Update: Annotated Checklist and Atlas of Taxonomy, Synonymy, Distribution, and Conservation Status. † = extinct.

See alsoList of Testudines families

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