Liopleurodon

Liopleurodon (; meaning 'smooth-sided teeth') is an extinct genus of carnivorous pliosaurid plesiosaurs that lived from the Callovian stage of the Middle Jurassic to the Kimmeridgian stage of the Late Jurassic period (approximately 166 to 155 million years ago). The type species is L. ferox, which is probably the only valid species. Some studies also include the second species L. pachydeirus, but this latter is considered as a probable junior synonym of L. ferox due to its lack of viable diagnosis. Fossils attributed to Liopleurodon, including some skeletons, are mainly known from Europe, with one occurrence reported in Mexico. As the holotype specimen of L. ferox consists of a single tooth preserving questionable distinctive features, recent studies therefore recommend the necessary identification of a neotype in order to preserve its validity. Other additional species were even proposed, but these are currently seen as coming from other pliosaurid genera. Like other plesiosaurs, Liopleurodon has four flippers, a short tail, and, like most pliosaurids, a long head and a short neck. In 1999, its size was greatly exaggerated in the BBC documentary series Walking with Dinosaurs, where it was depicted as reaching 25 m (82 ft) in length. However, the different attributed specimens show that the animal could reach a size ranging from 2.46 to 8.09 m (8 ft 1 in to 26 ft 7 in) long. Various studies show that Liopleurodon would have been an ambush predator, feeding on fish, cephalopods and other marine reptiles.

Research history

Even before Liopleurodon was named, material likely belonging to it was described in scientific literature. In 1838, Hermann von Meyer applied the name Ischyrodon meriani to a large tooth from possibly Callovian-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 a similar species, there was too little information available to make a confident assignment, so they treated Ischyrodon as a nomen dubium. In 1841, 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 Pliosaurus 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 1860, Hermann Trautschold assigned the name Pliosaurus giganteus to a small tooth that was discovered in the Moscow Basin of Russia, dating from the Oxfordian. This tooth is now thought to pertain to Liopleurodon, but the name Pliosaurus giganteus having already been used twice by this point, Trautschold's name is also invalid.

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