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 discovered in the López de Bertodano Formation, in Seymour Island, Antarctic Peninsula.

One of the distinguishing characteristics of this taxon is that it has well-marked heterodont dentition, a trait rarely present in mosasaurs and not found in other tylosaurines Fossil records show that Kaikaifilu lived in waters whose temperatures may have dropped below freezing.

The only known specimen of Kaikaifilu hervei, cataloged as SGO.PV.6509, was discovered in January 2011 by the Chilean Paleontological Expedition in the Upper Maastrichtian beds of the López de Bertodano Formation, located on Seymour Island, in the Antarctic Peninsula.

Fossil materials include several fragmentary parts of a skull, jawbone, 30 isolated teeth, and a partial left humerus.

[1] A new anatomical revision published in 2015 confirmed that the remains did indeed belong to a new genus and species,[2] that Otero and his colleagues described and scientifically named in 2017.

The specific epithet hervei is named in honor of Francisco Hervé, a Chilean geologist who made an important contribution to the knowledge of the geology of Chile and the Antarctic Peninsula.

[6][7] Although no estimate of body size was given in the academic description of the taxon in 2017, the accompanying press release noted that the animal would have reached approximately 10 m (390 in) in length.

They are conical in shape, have labial and lingual surfaces with smooth ridges extending from base to apex, lack serrated anterior carinae (cutting edges), and have a triangular-shaped lateral profile with crowns slightly curved backwards.

[1] As the fossils are fragmentary and incomplete, almost all the common features of the group are not present on them, making it impossible to directly assign Kaikaifilu within the Tylosaurinae.

[2] In the study officially describing it, all the analyzes carried out also find it as a tylosaurine, with similar results, only the most parsimonious cladogram classifying it as the most basal of the group.

[6][7] Kaikaifilu is known from Upper Maastrichtian deposits of the López de Bertodano Formation, located on Seymour Island, Antarctic Peninsula.

The depositional environment of López de Bertodano was divided into two main sections; a shallow estuary and a deeper continental shelf, both of which had their own separate invertebrate fauna.

[12][13] The López de Bertodano Formation is already known for the discovery of other genera of mosasaurs, including Moanasaurus, Mosasaurus, Liodon, Plioplatecarpus,[14] and some remains from undetermined tylosaurines.