''Kaikaifilusaurus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of rhynchocephalians in the family

Sphenodontidae Sphenodontidae is a family within the reptile group Rhynchocephalia, comprising taxa most closely related to the living tuatara of the genus ''Sphenodon''. Historically the taxa included within Sphenodontidae have varied greatly between analyse ...

from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger 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 ''creta'', ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...

. Fossils of the genus were found in Cenomanian sediments of the Candeleros Formation and

Turonian The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous Epoch, or a stage in the Upper Cretaceous Series. It spans the time between 93.9 ± 0.8 Ma and 89.8 ± 1 Ma (million years ago). The Turonian is preceded b ...

layers of the

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

, both of the

Neuquén Basin Neuquén Basin ( es, Cuenca Neuquina) 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 bas ...

and the

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/ Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0 ...

strata of the

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

in the

Cañadón Asfalto Basin The Cañadón Asfalto Basin ( es, Cuenca de Cañadón Asfalto) 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 for ...

, all in

Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

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

type species In 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 species that contains the biological type specime ...

''K. calvoi''.''Kaikaifilusaurus''
at Fossilworks.org

Etymology

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

Greek Greek may refer to: Greece 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 ...

''sauros'', meaning "lizard" and ''Kaikaifilu'', coming from Mapudungun, the language of the

Mapuche The Mapuche ( (Mapuche & Spanish: )) are a group of indigenous inhabitants of south-central Chile and southwestern Argentina, including parts of Patagonia. The collective term refers to a wide-ranging ethnicity composed of various groups who s ...

. In their cosmology, Kai-Kai filú 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 Greek ' meaning 'lizard') comprise a group of extinct, large marine reptiles from the Late Cretaceous. Their first fossil remains were discovered in a limestone quarry at Maastricht on ...

genus ''

Kaikaifilu ''Kaikaifilu'' is a genus of mosasaur from the Late Cretaceous part of the Lopez de Bertodano Formation of Antarctica, just before the Cretaceous–Paleogene extinction event. It is thought to be among the largest members of the tylosaurines, a ...

'' 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, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

.Otero et al., 2017, p.211

Classification

The present type species of ''Kaikaifilusaurus'', ''K. calvoi'', was described by Simón and Kellner 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 (plural novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", which is Latin for "new") that slowly fades over weeks or months. Causes of the dramat ...

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.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

Eilenodontinae Opisthodontia is a proposed clade of sphenodontian reptiles, uniting ''Opisthias'' from the Late Jurassic-earliest Cretaceous of Europe and North America with the Elienodontinae, a group of herbivorous sphenodontians known from the Late Triassic ...

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

arid A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ...

,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 be ...

comprised a playa lake with debris flows system, dominated by pyroclastic 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 (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

.Turtle Town, Cerro Barcino
at Fossilworks.org The fossil remains of ''Kaikaifilusaurus'' from the Candeleros Formation hail from Cenomanian fluvial red

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s and conglomerates.Araceli, on Bustingorry farm, Candeleros Formation
at Fossilworks.org The formation comprises eolian and

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

deposits, as well as sediments deposits in a braided river environment. Fossils of one of the largest theropods known, ''

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

'' 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 carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-frog" ''Triadobatrachus'' is ...

s, mammals and

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...

.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 Tetanurae, tetanuran theropod dinosaurs with controversial relations to other theropods. Its Derived (phylogenetics), derived members, the Megaraptoridae are noted for their elongated hand claws and proporti ...

ns. The

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

s ''

Gualicho shinyae ''Gualicho'' (named in reference to the gualichu) is a genus of theropod dinosaur. The type species is ''Gualicho shinyae''. It lived in what is now northern Patagonia, on what was then a South American island continent split off from the superco ...

'', ''

Argentinosaurus huinculensis ''Argentinosaurus'' 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 the largest known land animals o ...

'', '' Mapusaurus rosae'', '' Cathartesaura'',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 * * * * * * * *