Kaikaifilu

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. Ontogenetic analysis carried out on the fossils shows that they come from an adult individual. Shortly after the article was published, Otero reported that he and his colleagues accidentally used a non-royalty-free image in their description, an error that was later changed to another, entirely original image for their work. == Description ==

of Kaikaifilu as a tylosaurine As stored, portions of the holotype skull of Kaikaifilu hervei are around in length. Based on the skull of Taniwhasaurus antarcticus, a Campanian tylosaurine also known from Antarctica, the total length of Kaikaifilu's skull would be approximately between . This estimated length places it the largest known mosasaur in the Southern Hemisphere, as well as one of the largest tylosaurines identified to date. 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 in length. The preserved humerus of Kaikaifilu is incomplete, only known from the proximal half, but is very robust. The articular head has a tall, rectangular and dorso-ventrally broad pre-glenoid process. The pectoral ridge is also prominent and both structures are separated from the glenoid by respective grooves. == Classification ==

As soon as the discovery of the specimen SGO.PV.6509 was officially revealed in 2012, the preliminary descriptions already classified it in the subfamily Tylosaurinae, but could not determine whether the latter was a representative of a new taxon or not. 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. Nevertheless, one of the features present, namely the exclusion of the frontal from the margin of the orbit, is visible in this specimen. The first phylogenetic analysis of this specimen was performed in 2015, when the genus was still unnamed. All strict consensus methods place SGO.PV.6509 within the Tylosaurinae, but not always in the same position, the first analysis placing it in a basal position to Taniwhasaurus spp. and the second as a sister taxon to Tylosaurus. 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. The following cladogram is modified from the phylogenetic analysis conducted by Otero et al. (2017), showing the proposed placement of Kaikaifilu within Tylosaurinae: }} As of 2019, just two years after its official description, the attribution of Kaikaifilu to the Tylosaurinae has been questioned. The authors note that some observed characteristics do not appear to fit, or even contradict the definition of the group. In addition, the very fragmentary nature of the fossils prevents the same authors from carrying out new phylogenetic classifications with Kaikaifilu. == Paleoecology ==

|The López de Bertodano Formation (shown in light green), Seymour Island, Antarctica, where the fists fossils of Kaikaifilu have been found Kaikaifilu is known from Upper Maastrichtian deposits of the López de Bertodano Formation, located on Seymour Island, Antarctic Peninsula. Located within the polar circle at around 65°S, temperatures at medium to deep-shelf water conditions would have been around on average, while sea surface temperatures may have dropped below freezing and sea ice possibly formed at times. The López de Bertodano Formation is already known for the discovery of other genera of mosasaurs, including Moanasaurus, Mosasaurus, Liodon, Plioplatecarpus, and some remains from undetermined tylosaurines. The validity of some of these genera are disputed because they are mainly based on isolated teeth. Prognathodon and Globidens are also expected to be present based on distribution trends in the world of both genera, although conclusive fossils have yet to be found. Plesiosaurs from this formation would have been potential prey for Kaikaifilu, which, due to its large size, would probably have been an apex predator. A large ammonite fauna is known from this site, including the abnormal paperclip-shaped Diplomoceras. == See also ==