Geosaurus

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Geosaurus
Temporal range: Late Jurassic-Early Cretaceous, 150–136Ma
Geosaurus fossil.JPG
Fossil specimen
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Crocodylomorpha
Suborder: Thalattosuchia
Family: Metriorhynchidae
Tribe: Geosaurini
Genus: Geosaurus
Cuvier, 1824
Type species
Lacerta gigantea
Sömmerring, 1816
Species
  • G. giganteus
    (Sömmerring, 1816)
  • G. grandis
    (Wagner, 1858)
  • G. lapparenti
    Debelmas & Strannoloubsky, 1957
Synonyms
  • Halilimnosaurus Ritgen, 1826 [1]
  • Brachytaenius von Meyer, 1842 [2]

Geosaurus is an extinct genus of marine crocodyliform within the family Metriorhynchidae that lived during the Late Jurassic to 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 "Earth lizard", and is derived from the Greek Ge- ("Earth") and σαῦρος -sauros ("lizard"). The name Geosaurus was established by the French naturalist Georges Cuvier in 1824.[3]

The modern Chinese term for Geosaurus is Dilong 龍 "earth dragon" (龙 in simplified Chinese).[4] This contrasts to the dinosaur genus Dilong which was named from Chinese dilong 帝龍 "emperor dragon".

Description[edit]

Size of geosaurines

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.[5] 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 re-description of Geosaurus published in 2009 showed that these long-snouted form actually represent individuals of Cricosaurus.[6]

Classification and species[edit]

Genera considered junior synonyms of Geosaurus include Brachytaenius and Halilimnosaurus .[7] 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.[8][9] Although some traditional species, such as G. suevicus and G. araucanensis formed a natural group,[10] Enaliosuchus is also within that group.[8][11] 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.[6]

The species included below follow this revised classification, presented by Young and Andrade in 2009.[6]

Valid species[edit]

  • 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.[12]
  • 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 (eck and tail vertebrae and a partial pelvic girdle) from the Early Cretaceous (Valanginian) of France.[13] It was originally classified as a species of Dakosaurus.

A new, previously unknown large species of Geosaurus known only from a single tooth from the Nusplingen Plattenkalk of Germany.[14]

Cladogram after Cau & Fanti (2010).[15]

Geosaurus 

G. lapparenti




G. grandis



G. giganteus




Reclassified species[edit]

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,[16] G. vignaudi,[17] and G. araucanensis[18] were actually examples of the related Cricosaurus.[6] Rhacheosaurus gracilis, another long-snouted species, was also at one time considered a species of Geosaurus (as G. gracilis).[6][19]

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.[14]

An unnamed specimen classified as Geosaurus was found in Oxfordian age rocks of Cuba,[20] though further study has shown this species to be more closely related to Cricosaurus as well.[6]

Palaeobiology[edit]

Niche partitioning[edit]

Several species of metriorhynchids are known from the Mörnsheim Formation (Solnhofen limestone, early Tithonian) of Bavaria, Germany. Alongside Dakosaurus maximus, three species of Geosaurus are known, including G. giganteus, G. suevicus and G. 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 Dakosaurus and G. giganteus, which were large, short-snouted species with serrated teeth. The long-snouted G. suevicus and G. gracilis would have feed mostly on fish, although the more lightly built G. gracilis may have specialised towards feeding on small prey. In addition to four species of metriorhynchids, a moderate-sized species of Steneosaurus was also contemporaneous.[21]

From the slightly older Nusplingen Plattenkalk (late Kimmeridgian) of southern Germany, both G. suevicus and Dakosaurus maximus are contemporaneous. As with Solnhofen, G. suevicus feed upon fish, while Dakosaurus was the top predator.[22]

See also[edit]

References[edit]

  1. ^ Ritgen CH. 1826. Becken der krokodilartigen Salzumpf-eideche. Nova Acta Academiae Leopoldino-Carolinae Curios 13 (1): 331-358.
  2. ^ Meyer H von 1842. 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.
  3. ^ 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
  4. ^ Carr M. 1990. "Chinese Dragon Names". Linguistics of the Tibeto-Burman Area 13.2:87-189.
  5. ^ Fraas E. 1901. Die Meerkrokodile (Thalattosuchia n. g.) eine neue Sauriergruppe der Juraformation. Jahreshefte des Vereins für vaterländische Naturkunde, Württemberg 57: 409-418.
  6. ^ a b c d e f 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.
  7. ^ Steel R. 1973. Crocodylia. Handbuch der Paläoherpetologie, Teil 16. Stuttgart: Gustav Fischer Verlag, 116 pp.
  8. ^ a b Young MT. 2007. The evolution and interrelationships of Metriorhynchidae (Crocodyliformes, Thalattosuchia). Journal of Vertebrate Paleontology 27 (3): 170A.
  9. ^ Mueller-Töwe IJ. 2005. Phylogenetic relationships of the Thalattosuchia. Zitteliana A45: 211–213.
  10. ^ Gasparini Z, Pol D, Spalletti LA. 2006. An unusual marine crocodyliform from the Jurassic-Cretaceous boundary of Patagonia. Science 311: 70-73.
  11. ^ 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.
  12. ^ Sömmerring ST von. 1816. Ueber die Lacerta gigantea der Vorwelt. Denkschriften der Königlichen Akademie der Wisseschaften zu Münch 6: 37-59.
  13. ^ 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.
  14. ^ a b Andrade, M.B.D.; Young, M.T.; Desojo, J.B.; Brusatte, S.L. (2010). "The evolution of extreme hypercarnivory in Metriorhynchidae (Mesoeucrocodylia: Thalattosuchia) based on evidence from microscopic denticle morphology". Journal of Vertebrate Paleontology 30 (5): 1451–1465. doi:10.1080/02724634.2010.501442. 
  15. ^ Andrea Cau; Federico Fanti (2010). "The oldest known metriorhynchid crocodylian from the Middle Jurassic of North-eastern Italy: Neptunidraco ammoniticus gen. et sp. nov.". Gondwana Research 19. doi:10.1016/j.gr.2010.07.007. 
  16. ^ 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.
  17. ^ 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.
  18. ^ 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.
  19. ^ Meyer H von 1831. Neue fossile Reptilien aus der Ordung der Saurier. Nova Acta Academiae Leopoldino-Carolinae Curios 15 (2): 173-184.
  20. ^ 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.
  21. ^ 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
  22. ^ Dietl G, Dietl O, Schweigert G, Hugger R. 2000. Der Nusplinger Plattenkalk (Weißer Jura zeta) - Grabungskampagne 1999.