Name: Geosaurus ‭(‬Earth lizard‭)‬.
Phonetic: Jee-oh-sore-us.
Named By: Georges Cuvier‭ ‬-‭ ‬1824.
Synonyms: Brachytaenius,‭ ‬Halilimnosaurus.
Classification: Chordata,‭ ‬Reptilia,‭ ‬Archosauromorpha,‭ ‬Crurotarsi,‭ ‬Crocodylomorpha,‭ ‬Mesoeucrocodylia,‭ ‬Thalattosuchia,‭ ‬Metriorhynchidae.
Species: G.‭ ‬giganteus‭ (‬type‭)‬,‭ ‬G.‭ ‬grandis,‭ ‬G.‭ ‬lapparenti.
Diet: Piscivore.
Size: Around‭ ‬3‭ ‬meters long.
Known locations: France and Germany.
Time period: Tithonian of the Jurassic through to Valanginian of the Cretaceous.
Fossil representation: ‬Multiple specimen

       There is some confusion regarding Geosaurus reconstructions as there were once both long and short snouted forms of the genus.‭ ‬One former species of Geosaurus in particular known as G.‭ ‬suevicus was an almost complete specimen which was commonly used as a base for the majority of early Geosaurus reconstructions.‭ ‬Later analysis in‭ ‬2009‭ ‬by Mark T.‭ ‬Young and Marco Brandalise de Andrade however found this fossil to actually be a specimen of another marine crocodile named Cricosaurus.‭ ‬As such modern depictions of Geosaurus,‭ ‬find that it is actually more similar to Dakosaurus in appearance.
       As with Dakosaurus,‭ ‬Geosaurus is today thought to have been a short snouted marine crocodile that had large serrated teeth.‭ ‬With this kind of mouth and dentition,‭ ‬Geosaurus would have been a more effective predator of larger fish and potentially even other marine reptiles.‭ ‬Former species of Geosaurus which are now assigned to Cricosaurus indicate that this would have been a form of niche partitioning which allowed several species of marine crocodile to co-exist in the same ecosystem.‭ ‬This would see marine crocodiles like Geosaurus and Dakosaurus taking large prey,‭ ‬while Cricosaurus fed on prey like small fish which it could more easily catch with its longer jaws that had smaller but more numerous teeth.‭

Further reading
- Brachytaenius perennis aus dem dichten gelben Jurakalk von Aalen in Würtembertg. In: Meyer H von, Althaus GB, Münster G, eds. - Beiträge zur Petrefacten-kunde. Bayreuth: 22-23, & plate 7 - H. von Meyer - 1842.
- Découverte d’un crocodilien dans le Néocomien de La Martre (Var) Dacosaurus lapparenti n. sp. - Travaux du Laboratoire de la Faculté des Sciences de l'Université de Grenoble 33:89-99 - J. Debelmas & A. Strannoloubsky - 1957.
- Geosaurus vignaudi n. sp. (Crocodylia, Thalattosuchia), first evidence of metriorhynchid crocodilians in the Late Jurassic (Tithonian) of central-east Mexico (State of Puebla) - E. Frey, M. -C. Buchy, W. Stinnesbeck & J. G. López-Oliva - 2002.
- A new thalattosuchian crocodyliform from the Tithonian (Upper Jurassic) of northeastern Mexico - Comptes Rendus Palevol 5 (6): 785-794 - M. -C. Buchy, P. Vignaud, E. Frey, W. Stinnesbeck & A. H. G. González - 2006.
- The evolution and interrelationships of Metriorhynchidae (Crocodyliformes, Thalattosuchia). - Journal of Vertebrate Paleontology 27 (3): 170A - M. T. young - 2007.
- What is Geosaurus? Redescription of Geosaurus giganteus (Thalattosuchia: Metriorhynchidae) from the Upper Jurassic of Bayern, Germany. - Zoological Journal of the Linnean Society, 157: 551-585. - Mark T. Young & Marco Brandalise de Andrade - 2009.
- The oldest known metriorhynchid crocodylian from the Middle Jurassic of North-eastern Italy - Neptunidraco ammoniticus gen. et sp. nov.". Gondwana Research 19 - Andrea Cau & Federico Fanti - 2010.


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