Geosaurus Giganteus Holotype

''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 - ("lizard"). The name ''Geosaurus'' was established by the French naturalist Georges Cuvier in 1824.Cuvier G. 1824. Sur les ossements fossiles de crocodiles, 5. In: Dufour & D'Occagne, eds. ''Recherches sur les ossements fossiles, 2nd édition''. Paris: 143-160

Description

''Geosaurus'' was a large marine reptile of the group Crurotarsi, the line leading to modern crocodilians. It was about long and weighed . 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.Fraas E. 1901. Die Meerkrokodile (Thalattosuchia n. g.) eine neue Sauriergruppe der Juraformation. ''Jahreshefte des Vereins für vaterländische Naturkunde, Württemberg'' 57: 409-418. ''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''.Young, Mark T., and Marco Brandalise de Andrade, 2009. "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.

Classification and species

Genera considered junior synonyms of ''Geosaurus'' include ''Brachytaenius'' and ''Halilimnosaurus ''.Steel R. 1973. ''Crocodylia. Handbuch der Paläoherpetologie, Teil 16''. Stuttgart: Gustav Fischer Verlag, 116 pp. 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''.Young MT. 2007. The evolution and interrelationships of Metriorhynchidae (Crocodyliformes, Thalattosuchia). ''Journal of Vertebrate Paleontology'' 27 (3): 170A.Mueller-Töwe IJ. 2005. Phylogenetic relationships of the Thalattosuchia. ''Zitteliana'' A45: 211–213. Although some traditional species, such as ''G. suevicus'' and ''G. araucanensis'' formed a natural group,Gasparini Z, Pol D, Spalletti LA. 2006. An unusual marine crocodyliform from the Jurassic-Cretaceous boundary of Patagonia. ''Science'' 311: 70-73. ''Enaliosuchus'' is also within that group.Wilkinson LE, Young MT, Benton MJ. 2008. A new metriorhynchid crocodilian (Mesoeucrocodylia: Thalattosuchia) from the Kimmeridgian (Upper Jurassic) of Wiltshire, UK. ''Palaeontology'' 51 (6): 1307-1333. 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.

Valid species

* The type species ''Geosaurus giganteus'', meaning "giant Earth lizard", is known from Western Europe (Germany) of the Late Jurassic (Early Tithonian). It was originally named ''Lacerta gigantea'' by von Sömmerring.Sömmerring ST von. 1816. Ueber die ''Lacerta gigantea'' der Vorwelt. ''Denkschriften der Königlichen Akademie der Wisseschaften zu Münch'' 6: 37-59.
* ''Geosaurus grandis'', first described by Wagner in 1858, was formerly considered a species of ''Cricosaurus''. It is known from a complete skull.
* ''Geosaurus lapparenti'' is known from south-east France and dates to the early Cretaceous period ( Valanginian). It was named in honour of French palaeontologist Albert-Félix de Lapparent, and is based upon isolated skull and post-cranial bones (neck and tail vertebrae and a partial pelvic girdle) from the Early Cretaceous (Valanginian) of France.Debelmas J, Strannoloubsky A. 1957. Découverte d’un crocodilien dans le Néocomien de La Martre (Var) ''Dacosaurus lapparenti'' n. sp. ''Travaux Laboratoire de Géologie de l’université de Grenoble'' 33: 89-99. It was originally classified as a species of '' Dakosaurus''.

A large species of ''Geosaurus'' is known only from a single tooth from the Nusplingen Plattenkalk of Germany.

Cladogram after Cau & Fanti (2010).

Reclassified species

In 2009, Young and de Andrade published a re-description of ''Geosaurus'', examining its relationships and the validity of species lumped into the genus. After performing a phylogenetic analysis of metriorhynchids, they found that many species were grouped in a paraphyletic manner or with the wrong genera. Specifically, they found that several species formerly classified as ''Geosaurus'', including ''G. suevicus'', ''G. saltillense'',Buchy, M.-C., Vignaud, P., Frey, E., Stinnesbeck, W. & González, A.H.G. 2006. A new thalattosuchian crocodyliform from the Tithonian (Upper Jurassic) of northeastern Mexico. ''Comptes Rendus Palevol'' 5 (6): 785-794. ''G. vignaudi'',Frey, E., Buchy, M.-C., Stinnesbeck, W. & López-Oliva, J.G. 2002. ''Geosaurus vignaudi'' n. sp. (Crocodylia, Thalattosuchia), first evidence of metriorhynchid crocodilians in the Late Jurassic (Tithonian) of central-east Mexico (State of Puebla). ''Canadian Journal of Earth Sciences'' 39: 1467–1483. and ''G. araucanensis''Gasparini ZB, Dellapé D. 1976. Un nuevo cocodrilo marino (Thalattosuchia, Metriorhynchidae) de la Formación Vaca Muerta (Jurasico, Tithoniano) de la Provincia de Neuquén (República Argentina). ''Congreso Geológico Chileno'' 1: c1-c21. were actually examples of the related ''Cricosaurus''. ''Rhacheosaurus gracilis'', another long-snouted species, was also at one time considered a species of ''Geosaurus'' (as ''G. gracilis'').Meyer H von 1831. Neue fossile Reptilien aus der Ordung der Saurier. ''Nova Acta Academiae Leopoldino-Carolinae Curios'' 15 (2): 173-184.

''Geosaurus carpenteri'', also formerly referred to ''Dakosaurus'', is known from a partial skull. Teeth identical to the known teeth of this species are also known from Yorkshire, UK. It was assigned to its own genus, ''Torvoneustes'' by Andrade ''et al.'', 2010.

An unnamed specimen classified as ''Geosaurus'' was found in the Oxfordian Jagua Formation of Cuba,Gasparini ZB, Iturralde-Vinet M. 2001. Metriorhynchid crocodiles (Crocodyliformes) from the Oxfordian of Western cuba. ''Neues Jahrbuch für Geologie und Paläontologie, Monatshefte'' 9: 534–542. though further study has shown this species to be more closely related to ''Cricosaurus'' as well.

Additionally, ''Geosaurus'' fossils have been reported from the Vaca Muerta of Argentina.''Geosaurus''
at Fossilworks.org

Palaeobiology

Niche partitioning

Several species of metriorhynchids are known from the Mörnsheim Formation ( Solnhofen limestone, early Tithonian) of Bavaria, Germany: ''Geosaurus giganteus'', ''Dakosaurus maximus'', '' Cricosaurus suevicus'' and ''Rhacheosaurus gracilis''. It has been hypothesised that niche partitioning enabled several species of crocodyliforms to co-exist. The top predators of this Formation appear to be ''G. giganteus'' and ''D. maximus'', which were large, short-snouted species with serrated teeth. The long-snouted ''C. suevicus'' and ''R. gracilis'' would have fed mostly on fish, although the more lightly built ''Rhacheosaurus'' may have specialised towards feeding on small prey. In addition to these four species of metriorhynchids, a moderate-sized species of '' Steneosaurus'' was also contemporaneous.Andrade MB, Young MT. 2008
High diversity of thalattosuchian crocodylians and the niche partition in the Solnhofen Sea
. The 56th Symposium of Vertebrate Palaeontology and Comparative Anatomy

See also

* List of marine reptiles

References

{{Taxonbar, from=Q1901163

Prehistoric pseudosuchian genera
Prehistoric marine crocodylomorphs
Late Jurassic crocodylomorphs
Early Cretaceous crocodylomorphs of Europe
Jurassic reptiles of Europe
Jurassic France
Fossils of France
Jurassic Germany
Fossils of Germany
Solnhofen fauna
Jurassic United Kingdom
Fossils of England
Mesozoic reptiles of North America
Jurassic Cuba
Fossils of Cuba
Mesozoic reptiles of South America
Jurassic Argentina
Cretaceous Argentina
Fossils of Argentina
Fossil taxa described in 1824
Taxa named by Georges Cuvier