''Kaikaifilusaurus'' is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

rhynchocephalia Rhynchocephalia (; ) is an order of lizard-like reptiles that includes only one living species, the tuatara (''Sphenodon punctatus'') of New Zealand. Despite its current lack of diversity, during the Mesozoic rhynchocephalians were a speciose g ...

ns in the family

Sphenodontidae Sphenodontidae is a family within the reptile group Rhynchocephalia, comprising taxa most closely related to the living tuatara (''Sphenodon punctatus''). Historically the taxa included within Sphenodontidae have varied greatly between analyses, ...

from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

. Fossils of the genus were found in

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

sediments of the

Candeleros Formation The Candeleros Formation is a geologic formation that outcrop, crops out in the Rio Negro Province, Río Negro, Neuquen Province, Neuquén, and Mendoza Province, Mendoza provinces of northern Patagonia, Argentina. It is the oldest formation in the ...

and

Turonian The Turonian is, in the International Commission on Stratigraphy, ICS' geologic timescale, the second age (geology), age in the Late Cretaceous epoch (geology), Epoch, or a stage (stratigraphy), stage in the Upper Cretaceous series (stratigraphy), ...

layers of the

Huincul Formation The Huincul Formation is a geologic formation of Late Cretaceous (Cenomanian to Turonian, Early Turonian) age of the Neuquén Basin that outcrops in the Mendoza Province, Mendoza, Rio Negro Province, Río Negro and Neuquén Provinces of northern ...

, both of the

Neuquén Basin Neuquén Basin () is a sedimentary basin covering most of Neuquén Province in Argentina. The basin originated in the Jurassic and developed through alternating continental and marine conditions well into the Tertiary. The basin bounds to the wes ...

and the

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

strata of the

Cerro Barcino Formation The Cerro Barcino Formation (also known as the Gorro Frigio Formation) is a geological Formation (geology), formation in South America whose strata span the Early Cretaceous to the earliest Late Cretaceous. The top age for the formation has been e ...

in the

Cañadón Asfalto Basin The Cañadón Asfalto Basin () is an irregularly shaped sedimentary basin located in north-central Patagonia, Argentina. The basin stretches from and partly covers the North Patagonian Massif in the north, a high forming the boundary of the basin ...

, all in

Patagonia Patagonia () is a geographical region that includes parts of Argentina and Chile at the southern end of South America. The region includes the southern section of the Andes mountain chain with lakes, fjords, temperate rainforests, and glaciers ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. The genus contains two species, ''K. minimus'' and the

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

''K. calvoi''.''Kaikaifilusaurus''
at

Fossilworks Fossilworks was a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cr ...

.org

Etymology

The genus name ''Kaikaifilusaurus'' is derived from the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

''sauros'', meaning "lizard" and ''Kaikaifilu'', coming from

Mapudungun Mapuche ( , ; from 'land' and 'people', meaning 'the people of the land') or Mapudungun (from 'land' and 'speak, speech', meaning 'the speech of the land'; also spelled Mapuzugun and Mapudungu) is either a language isolate or member of the s ...

, the language of the

Mapuche The Mapuche ( , ) also known as Araucanians are a group of Indigenous peoples of the Americas, Indigenous inhabitants of south-central Chile and southwestern Argentina, including parts of Patagonia. The collective term refers to a wide-ranging e ...

. In their cosmology,

Kai-Kai filú Coi Coi-Vilu or Caicai-Vilu/Cai Cai Vilu (from ; ''Kaykay'', a name, and ''filu'', "snake") is the Mapuche god of water (or goddess, in some versions found in Chiloé) and, according to Mapuche myths (later also found in Chiloé), supreme rule ...

is the almighty giant reptile owner of the seas, a rival of Treng-Treng filú, "both creators of the lands through their continuous fight that causes the earthquakes, volcanoes, tsunamis and all the events that molded the earth where we live". The same etymology has been used for the

mosasaur Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Ancient Greek, Greek ' meaning 'lizard') are an extinct group of large aquatic reptiles within the family Mosasauridae that lived during the Late Cretaceous. Their first fossil remains wer ...

genus ''

Kaikaifilu ''Kaikaifilu'' is an extinct genus of large mosasaurs that lived during the Maastrichtian stage of the Late Cretaceous, in what is now northern Antarctica. The only species known, ''K. hervei'', was described in 2017 from an incomplete specimen d ...

'' from the Lopez de Bertodano Formation of

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

.Otero et al., 2017, p.211

Classification

The present type species of ''Kaikaifilusaurus'', ''K. calvoi'', was described by Simón and

Kellner Kellner is a German surname literally meaning "waiter". Notable people with the surname include: * Ádám Kellner (born 1986), Hungarian tennis player * Alex Kellner (1924–1996), baseball pitcher * Alexander Kellner (born 1961), Brazilian paleon ...

in 2003, based on type specimen MPCHv 4, a mandible (left lower jaw) from the Candeleros Formation. In the same year, ''Priosphenodon avelasi'' was described by Apesteguía and

Novas A nova ( novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", Latin for "new") that slowly fades over weeks or months. All observed novae involve white d ...

in 2003, based on type specimen MPCA 300, a partially articulated adult skeleton from the Cenomanian fluvial sandstones of the Candeleros Formation in the Neuquén Basin. Gentil et al. in 2019 reassigned ''P. avelasi'' as a junior synonym of ''Kaikaifilusaurus calvoi''. Gentil et al. placed the second species of ''Priosphenodon'', ''P. minimus'', in 2014 described by Apesteguía and Carballido based on the type specimen MPEF-PV 3166, a skull (almost complete skull with attached jaws, from the Albian Cerro Barcino Formation of the Cañadón Asfalto Basin,Apesteguía & Carballido, 2014, p.304 in the same genus of ''Kaikaifilusaurus'' as ''K. minimus''. Apesteguía and Carballido had considered ''Kaikaifilusaurus'' a

nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium,'' it may be impossible to determine whether a ...

.Gentil et al., 2019, p.74 The 2019 researchers described another specimen of ''Kaikaifilusaurus''; MPCA-PV 808, an incomplete right dentary from the Turonian strata of the Huincul Formation of the Neuquén Basin.Gentil et al., 2019, p.73 Gentil et al. (2019) place the genus ''Kaikaifilusaurus'' in the

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...

Eilenodontinae Eilenodontinae are an extinct clade of reptiles belonging to Sphenodontia. They are either considered a subgroup of Opisthodontia, or Sphenodontidae. They had deep jaws with broad, closely packed teeth with thick enamel and noticeable wear fac ...

of the order Sphenodontia.

Description

The fossil of ''Kaikaifilusaurus'' sp. described by Gentil et al. in 2019 comprises a fragment of long preserving nine teeth, presenting an acrodont implantation and a nearly straight anteroposterior linear arrangement. Adult specimens of ''Kaikaifilusaurus'' are estimated to reach in length, larger than previously known terrestrial sphenodontian.Apesteguía & Novas, 2003, p.609

Paleoecology

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 ...

of ''Kaikaifilusaurus'' ranges from the

to the

, straddling the boundary between the

Early Early may refer to: Places in the United States * Early, Iowa, a city * Early, Texas, a city * Early Branch, a stream in Missouri * Early County, Georgia * Fort Early, Georgia, an early 19th century fort Music * Early B, stage name of Jamaican d ...

and

. The oldest record (the ''K. minimus'' type locality) of the genus comes from the La Paloma Member of the

of the

in north-central

, Argentina.Tres Cerros; ''Priosphenodon minimus'' type locality
at

.org During this time, the paleoclimate of the La Paloma Member of the formation was

arid Aridity is the condition of geographical regions which make up approximately 43% of total global available land area, characterized by low annual precipitation, increased temperatures, and limited water availability.Perez-Aguilar, L. Y., Plata ...

,Rauhut et al., 2003, p.495 and the

depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will b ...

comprised a playa lake with debris flows system, dominated by

pyroclastic Pyroclast, Pyroclastic or Pyroclastics may refer to: Geology * Pyroclast, or airborne volcanic tephra fragments * Pyroclastic rock, rock fragments produced and ejected by explosive volcanic eruptions * Pyroclastic cone, landform of ejecta fro ...

deposits with intercalated dune sediments.Rauhut et al., 2003, p.491 The same member has provided fossils of '' Chubutemys copelloi'' and an indeterminate

theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

.Turtle Town, Cerro Barcino
at

.org The fossil remains of ''Kaikaifilusaurus'' from the

hail from

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

red

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

s and conglomerates.Araceli, on Bustingorry farm, Candeleros Formation
at

.org The formation comprises eolian and

paleosol In Earth science, geoscience, paleosol (''palaeosol'' in Great Britain and Australia) is an ancient soil that formed in the past. The definition of the term in geology and paleontology is slightly different from its use in soil science. In geo ...

deposits, as well as sediments deposits in a

braided river A braided river (also called braided channel or braided stream) consists of a network of river channel (geography), channels separated by small, often temporary, islands called ''braid bars'' or, in British English usage, ''aits'' or ''eyots''. ...

environment. Fossils of one of the largest theropods known, ''

Giganotosaurus carolinii ''Giganotosaurus'' ( ) is a genus of large theropod dinosaur that lived in what is now Argentina, during the early Cenomanian age of the Late Cretaceous period (geology), period, approximately 99.6 to 95 million years ago. The holotype specim ...

'' were found in this succession,Sánchez et al., 2006, p.4 as well as

frog A frog is any member of a diverse and largely semiaquatic group of short-bodied, tailless amphibian vertebrates composing the order (biology), order Anura (coming from the Ancient Greek , literally 'without tail'). Frog species with rough ski ...

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s and

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

.Leanza, 2004, p.68 The youngest record of the genus occurs in the

, overlying the Candeleros Formation in

. The formation represents an arid environment with ephemeral or seasonal streams. The same locality where ''Kaikaifilusaurus'' was found, has provided abundant fossils of lepisosteid fish, chelid turtles, lizards, neosuchian crocodyliforms, ornithopods, titanosaurian sauropods and diverse theropods including

abelisaurid Abelisauridae (meaning "Abel's lizards") is a family (or clade) of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous period, on the ancient southern supercontinent of Gondwana, and today their fossil remains are foun ...

carcharodontosaurid Carcharodontosauridae (carcharodontosaurids; from the Greek καρχαροδοντόσαυρος, ''carcharodontósauros'': "shark-toothed lizards") is a group of carnivorous theropod dinosaurs. In 1931, Ernst Stromer named Carcharodontosauridae ...

s, and

megaraptora Megaraptora is a clade of carnivorous theropod dinosaurs. Its derived members, the Megaraptoridae are noted for their large hand claws and powerfully-built forelimbs, which are usually reduced in size in other large theropods. Although undoubt ...

ns. The

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

s '' Gualicho shinyae'', ''

Argentinosaurus huinculensis ''Argentinosaurus'' (meaning "lizard from Argentina") is a genus of giant sauropod dinosaur that lived during the Late Cretaceous period in what is now Argentina. Although it is only known from fragmentary remains, ''Argentinosaurus'' is one of ...

'', '' Mapusaurus rosae'', ''

Cathartesaura ''Cathartesaura'' is a genus of rebbachisaurid sauropod dinosaur hailing from the Late Cretaceous strata of the Huincul Formation, at the "La Buitrera" locality, in the Neuquén Basin of Río Negro Province, Argentina. The fossil remains, describ ...

'',Gallina & Apesteguía, 2005 p.154 '' Ilokelesia'',Coria & Salgado, 1998, p.91 and '' Skorpiovenator bustingorryi'',Canale et al., 2008, p.410 come from this formation.Apesteguía et al., 2016, p.2

References

Bibliography

;''Kaikaifilusaurus'' * * * * * ;Paleoecology * * * * * * * *