Geosaurus

Geosaurus is an extinct genus of marine crocodyliform within the family Metriorhynchidae, that lived during the Late Jurassic and the Early Cretaceous. Geosaurus was a carnivore that spent much, if not all, its life out at sea. No Geosaurus eggs or nests have been discovered, so little is known of the reptile's lifecycle, unlike other large marine reptiles of the Mesozoic, such as plesiosaurs or ichthyosaurs which are known to give birth to live young out at sea. Where Geosaurus mated, whether on land or at sea, is currently unknown. The name Geosaurus means 'Mother of Giants lizard', and is derived from the Greek Ge- ('Earth', the mythical mother of the Giants) and σαῦρος -sauros ('lizard'). The name Geosaurus was established by the French naturalist Georges Cuvier in 1824. Geosaurus was a large, marine reptile of the group Crurotarsi, the line leading to modern crocodilians. Specifically, it was a 'marine crocodile', or thalattosuchian. Geosaurus was similar in appearance to the related Dakosaurus with a relatively short skull and curved teeth designed for slashing, which it likely used to attack large prey. Many early depictions of Geosaurus were based on a nearly complete specimen described by Eberhard Fraas, which Fraas classified as a distinct species of Geosaurus, G. suevicus. This specimen was found in Germany and dated to the late Jurassic (Late Kimmeridgian) period. G. suevicus had a distinctively long, narrow snout filled with small, pointed teeth very different from skulls belonging to the type species. Further study and a redescription of Geosaurus published in 2009 showed that these long-snouted forms actually represent individuals of Cricosaurus. Genera considered junior synonyms of Geosaurus include Brachytaenius and Halilimnosaurus . Numerous species had been assigned to this genus since the 19th Century. However, phylogenetic analyses begun in 2005 did not support the monophyly of Geosaurus. Although some traditional species, such as G. suevicus and G. araucanensis formed a natural group, Enaliosuchus is also within that group. This, as well as further study showing that traditional metriorhynchid genera were not grouped based on actual relationships, necessitated almost all traditional species being removed from Geosaurus and reclassified elsewhere, as well as several species previously placed in other genera to be reclassified as species of Geosaurus. The species included below follow this revised classification, presented by Young and Andrade in 2009. A large species of Geosaurus is known only from a single tooth from the Nusplingen Plattenkalk of Germany. Cladogram after Cau & Fanti (2010).