Liopleurodon (; meaning 'smooth-sided teeth') is an extinct genus of large, carnivorous marine reptile belonging to the Thalassophonea, a clade of short-necked pliosaurid plesiosaurs. Liopleurodon lived from the Callovian Stage of the Middle Jurassic to the Kimmeridgian stage of the Late Jurassic Period (c. 166 to 155 mya). It was the apex predator of the Middle to Late Jurassic seas that covered Europe. The largest species, L. ferox, is estimated to have grown up to in length based on the largest known skull. The name "Liopleurodon" (meaning "smooth-sided tooth") derives from Ancient Greek words: , "smooth"; , "side" or "rib"; and , "tooth". Discovery and species Even before Liopleurodon was named, material likely belonging to it was described. In 1841, Hermann von Meyer named the species Thaumatosaurus oolithicus based on a fragmentary specimen consisting of partial teeth, skull elements, vertebrae, and ribs from deposits in Württemberg, Germany, possibly dating to the Oxfordian. However, this material is nondiagnostic, lacking distinguishing features. Johann Andreas Wagner published a description of a large plesiosaur tooth from Bavaria, Germany, in 1852, assigning it to a new species that he named Pliosaurus giganteus. However, in 1824, William Conybeare had named a species of Plesiosaurus, Plesiosaurus giganteus, and this species was later viewed as a synonym of either Pliosaurus brachydeirus or P. brachyspondylus by following authors. Since the name Pliosaurus giganteus had been used prior to Wagner's publication, Wagner's name is invalid due to preoccupation. In 1838, Hermann von Meyer applied the name Ischyrodon meriani to a large tooth from Oxfordian-aged rocks in Fricktal, Switzerland. This tooth lacks identifying characteristics, and therefore it is not clear what it belonged to, although Lambert Beverly Tarlo noted the possibility of it pertaining to Liopleurodon in 1960. A 2022 study by Daniel Madzia and colleagues noted that while the tooth likely came from Liopleurodon or something similar, there was too little information available to make a confident assignment, so they treated Ischyrodon as a nomen dubium. In 1860, Hermann Trautschold assigned the name Pliosaurus giganteus to a small tooth now thought to pertain to Liopleurodon. However, as the name Pliosaurus giganteus had already been used twice by this point, Trautschold's name is also invalid. The genus name Liopleurodon was coined by Henri Émile Sauvage in 1873. Sauvage named three species which he assigned to this genus, each based on a single tooth. One tooth, its crown measuring long, was found