Kaikaifilusaurus

Kaikaifilusaurus is an extinct genus of rhynchocephalians in the family Sphenodontidae from the Late Cretaceous of South America. Fossils of the genus were found in Cenomanian sediments of the Candeleros Formation and Turonian layers of the Huincul Formation, both of the Neuquén Basin and the Albian strata of the Cerro Barcino Formation in the Cañadón Asfalto Basin, all in Patagonia, Argentina. The genus contains two species, "K. minimus" and the type species "K. calvoi".
Etymology.
The genus name "Kaikaifilusaurus" is derived from the Greek "sauros", meaning "lizard" and "Kaikaifilu", coming from Mapudungun, the language of the Mapuche. 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 genus "Kaikaifilu" from the Lopez de Bertodano Formation of Antarctica.
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 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, in the same genus of "Kaikaifilusaurus" as "K. minimus". Apesteguía and Carballido had considered "Kaikaifilusaurus" a nomen dubium.
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) place the genus "Kaikaifilusaurus" in the subfamily Eilenodontinae 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.
Paleoecology.
The fossil record of "Kaikaifilusaurus" ranges from the Albian to the Turonian, straddling the boundary between the Early and Late Cretaceous. The oldest record (the "K. minimus" type locality) of the genus comes from the La Paloma Member of the Cerro Barcino Formation of the Cañadón Asfalto Basin in north-central Patagonia, Argentina. During this time, the paleoclimate of the La Paloma Member of the formation was arid, and the depositional environment comprised a playa lake with debris flows system, dominated by pyroclastic deposits with intercalated dune sediments. The same member has provided fossils of "Chubutemys copelloi" and an indeterminate theropod.
The fossil remains of "Kaikaifilusaurus" from the Candeleros Formation hail from Cenomanian fluvial red sandstones and conglomerates. The formation comprises eolian and paleosol deposits, as well as sediments deposits in a braided river environment. Fossils of one of the largest theropods known, "Giganotosaurus carolinii" were found in this succession, as well as frogs, mammals and fish.
The youngest record of the genus occurs in the Huincul Formation, overlying the Candeleros Formation in Neuquén Basin. 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 abelisaurids, carcharodontosaurids, and megaraptorans. The dinosaurs "Gualicho shinyae", "Argentinosaurus huinculensis", "Mapusaurus rosae", "Cathartesaura", "Ilokelesia", and "Skorpiovenator bustingorryi", come from this formation.