Kronosaurus

Kronosaurus; Temporal range: Aptian-Late Albian; ~
	QM F18827, the skull of one of the proposed neotype specimens of K. queenslandicus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	†Sauropterygia
Order:	†Plesiosauria
Family:	†Pliosauridae
Subfamily:	†Brachaucheninae
Genus:	†Kronosaurus; Longman, 1924
Type species
	†Kronosaurus queenslandicus; Longman, 1924
Synonyms
	Eiectus longmani ? Noè & Gómez-Pérez, 2022;

Kronosaurus (/ˌkrɒnoʊˈsɔːrəs/ KRON-oh-SOR-əs) is an extinct genus of large short-necked pliosaur that lived during the Aptian to Albian stages of the Early Cretaceous in what is now Australia. The first known specimen was received in 1899 and consists of a partially preserved mandibular symphysis, which was first thought to come from an ichthyosaur according to Charles De Vis. However, it was 1924 that Albert Heber Longman formally described this specimen as the holotype of an imposing pliosaurid, to which he gave the scientific name K. queenslandicus, which is still the only recognized species nowadays. The genus name, meaning "lizard of Kronos", refers to its large size and possible ferocity reminiscent of the Titan of the Greek mythology, while the species name alludes to Queensland, the Australian state of its discovery. In the early 1930s, the Harvard Museum of Comparative Zoology sent an organized expedition to Australia that recovered two specimens historically attributed to the taxon, including a well known skeleton that is now massively restored in plaster. Several attributed fossils were subsequently discovered, including two large, more or less preserved skeletons. As the holotype specimen does not present diagnostics to concretely distinguish Kronosaurus from other pliosaurids, these same two skeletons are proposed as potential neotypes for future redescriptions. Two additional species were proposed, but these are now seen as unlikely or belonging to another genus.

Kronosaurus is one of the largest known pliosaurs identified to date. Initial estimates set its maximum size at around 13 m (43 ft) long based on the Harvard skeleton. However, the latter having been reconstructed with an exaggerated number of vertebrae, estimates published from the early 2000s reduce the size of the animal from 9 m (30 ft) to more than 10 m (33 ft) long. Like all plesiosaurs, Kronosaurus has four paddle-like limbs, a short tail and, like most pliosaurids, a long head and a short neck. The largest identified skulls of Kronosaurus dwarf those of largest known theropod dinosaurs in size. The front of the skull is elongated into a narrow rostrum (snout). The mandibular symphysis, where the front ends of each side of the mandible (lower jaw) fuse, is elongated in Kronosaurus, and contains up to six pairs of teeth. The large cone-shaped teeth of Kronosaurus would have been used for a diet consisting of large prey. The front teeth are larger than the back teeth. The limbs of Kronosaurus were modified into flippers, with the back pair larger than the front. The flippers would have given a wingspan of more than 5 m (16 ft) for the largest representatives.

Phylogenetic classifications published since 2013 recover Kronosaurus within the subfamily Brachaucheninae, a lineage which includes numerous pliosaurids that lived during different stages of the Cretaceous. Based on its stratigraphic distribution in the fossil record, Kronosaurus inhabited the Eromanga Sea, an ancient inland sea that covered a large part of Australia during the Early Cretaceous. This inner sea reached cold temperatures close to freezing. Kronosaurus would likely have been an apex predator in this sea, with fossil evidence showing that it preyed on sea turtles and other plesiosaurs. Estimates of its bite force suggest that the animal would have reached between 15,000 to 27,000 newtons (3,370 to 6,070 lbf), surpassing the placoderm Dunkleosteus and rivaling Tyrannosaurus, but being largely outnumbered by the megalodon. The skull of a juvenile specimen shows that it would have been attacked by an adult, indicating intraspecific aggression or even potential evidence of cannibalism within the genus. Kronosaurus would have faced interspecific competition with other large predators within this sea, with one specimen attributed showing bite marks from a Cretoxyrhina-like shark.