''Pelagosaurus'' (meaning "lizard of the open sea") is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

thalattosuchia Thalattosuchia is a clade of marine crocodylomorphs from the Early Jurassic to the Early Cretaceous that had a cosmopolitan distribution. They are colloquially referred to as marine crocodiles or sea crocodiles, though they are not members of Cro ...

n crocodyliform that lived during the

Toarcian The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian. The Toarcian ...

stage of the

Lower Jurassic The Early Jurassic Epoch (in chronostratigraphy corresponding to the Lower Jurassic Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-Jurassic extinction event, 201.3 Ma ...

, around 183 Ma to 176 Ma (million years ago), in shallow

epicontinental sea An inland sea (also known as an epeiric sea or an epicontinental sea) is a continental body of water which is very large and is either completely surrounded by dry land or connected to an ocean by a river, strait, or "arm of the sea". An inland s ...

s that covered much of what is now

Western Europe Western Europe is the western region of Europe. The region's countries and territories vary depending on context. The concept of "the West" appeared in Europe in juxtaposition to "the East" and originally applied to the ancient Mediterranean ...

. The systematic taxonomy of ''Pelagosaurus'' has been fiercely disputed over the years, and was assigned to Thalattosuchia after its systematics within

Teleosauridae Teleosauridae is a family of extinct typically marine crocodylomorphs similar to the modern gharial that lived during the Jurassic period. Teleosaurids were thalattosuchians closely related to the fully aquatic metriorhynchoids, but were less ad ...

were disputed. ''Pelagosaurus'' measured long and weighed .

Discovery

''Pelagosaurus'' was originally described from a specimen from

Normandy Normandy (; french: link=no, Normandie ; nrf, Normaundie, Nouormandie ; from Old French , plural of ''Normant'', originally from the word for "northman" in several Scandinavian languages) is a geographical and cultural region in Northwestern ...

, but the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

for ''P. typus'' was discovered north of the town of

Ilminster Ilminster is a minster town and civil parish in the South Somerset district of Somerset, England, with a population of 5,808. Bypassed in 1988, the town now lies just east of the junction of the A303 (London to Exeter) and the A358 (Taunton to ...

Somerset, England ( en, All The People of Somerset) , locator_map = , coordinates = , region = South West England , established_date = Ancient , established_by = , preceded_by = , origin = , lord_lieutenant_office =Lord Lieutenant of Somerset , lord_ ...

. Most ''Pelagosaurus'' remains have been found in the Ilminster area, but numerous other remains, predominantly

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

s and articulated

skeleton A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

s, have been found around Western Europe in locations such as

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

, and

Switzerland ). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are installed in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel ...

. Specimens from the Somerset region come primarily from the Strawberry Bank quarry north of Ilminster; although the site had yielded other fossil remains before, the site has since been built over. One of the specimens was that of a small juvenile, providing some insight into ''Pelagosaurus''' growth pattern.Pierce SE, Benton MJ. 2006. ''Pelagosaurus typus'' Bronn, 1841 (Mesoeucrocodylia: Thalattosuchia) from the Upper Lias (Toarcian, Lower Jurassic) of Somerset, England. ''Journal of Vertebrate Paleontology'' 26 (3): 621–635.

Evolutionary relationships

The evolutionary relationships of ''Pelagosaurus'' has been confusing as there have been three different interpretations of its placement in

Thalattosuchia Thalattosuchia is a clade of marine crocodylomorphs from the Early Jurassic to the Early Cretaceous that had a cosmopolitan distribution. They are colloquially referred to as marine crocodiles or sea crocodiles, though they are not members of Cro ...

. ''Pelagosaurus'' was initially classified as a

teleosaurid Teleosauridae is a family of extinct typically marine crocodylomorphs similar to the modern gharial that lived during the Jurassic period. Teleosaurids were thalattosuchians closely related to the fully aquatic metriorhynchoids, but were less ad ...

, based upon anatomical similarity, by Eudes-Deslongchamps, Westphal and Duffin.Eudes-Deslongchamps JAE. 1863. "Mémoire sur les Téléosauriens de l’époque Jurassique du Département de Calvados". ''Mémoires de la Société Linnéenne de Normandie'' 13:1–138.Eudes-Deslongchamps EE. 1877. ''Le Jura Normand'', 4. F. Savy (ed). Paris. 60 p.Westphal F. 1961. "Zur Systematik der deutschen und englischen Lias Krokodilier". ''Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen'' 113:207–217.Westphal F. 1962. Die Krokodilen des deutschen und englischen oberen Lias. ''Palaeontographica, Abteilung A'' 118:1–96.Duffin CJ. 1979. "''Pelagosaurus'' (Mesosuchia, Crocodilia) from the English Toarcian (Lower Jurassic)". ''Neues Jahrbuch für Geologie und Paläontologie, Monatshefte'' 1979:475–485. Its position as a basal

metriorhynchid Metriorhynchidae is an extinct family of specialized, aquatic metriorhynchoid crocodyliforms from the Middle Jurassic to the Early Cretaceous period (Bajocian to early Aptian) of Europe, North America and South America. The name Metriorhynchidae ...

was suggested by Eric Buffetaut in 1980.Buffetaut E. 1980. Position systématique et phylogénetique du genre ''Pelagosaurus'' Bronn, 1841 (Crocodylia, Mesosuchia), du Toarcian d’Europe. ''Geobios'' 13:783–786.Buffetaut E. 1982. Radiation évolutive, paléoécologie et biogéographie des crocodiliens mésosuchiens. ''Mémoires de la Sociéte Géologique de France'' 42:1–88. However,

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analyses from the 1980s, 1990s and early 2000s found ''Pelagosaurus'' to be the sister taxon to both Teleosauridae and Metriorhynchidae.Benton MJ, Clark JM. 1988. Archosaur phylogeny and the relationships of the Crocodylia; pp. 295–338 in MJ. Benton (ed.), ''The phylogeny and classification of the tetrapods, Vol. 1. Amphibians, Reptiles, Birds''. Systematic Association Special Volume 35A. Clarendon Press, Oxford.Clark JM. 1994. Patterns of evolution in Mesozoic Crocodyliformes; pp. 84–97 in NC. Fraser and H-D. Sues (eds.), ''In the shadow of the dinosaurs: Early Mesozoic tetrapods''. Cambridge University Press, Cambridge and New York.Buckley GA, Brochu CA, Krause DW, Pol D. 2000. A pugnosed crocodyliform from the Late Cretaceous of Madagascar. ''Nature'' 405:941–944. The most recent

analyses have all found ''Pelagosaurus'' to be a basal teleosaurid,Mueller-Töwe IJ. 2005. Phylogenetic relationships of the Thalattosuchia. ''Zitteliana'' A45: 211–213.Gasparini Z, Pol D, Spalletti LA. 2006. An unusual marine crocodyliform from the Jurassic-Cretaceous boundary of Patagonia. ''Science'' 311: 70-73.Young MT. 2007. The evolution and interrelationships of Metriorhynchidae (Crocodyliformes, Thalattosuchia). ''Journal of Vertebrate Paleontology'' 27 (3): 170A. rather than a basal metriorhynchid or thalattosuchian.

Palaeobiology

''Pelagosaurus'' was well adapted to aquatic life; it had developed a long, streamlined snout, a tail with fin-like attributes and paddle-like limbs for swimming in the warm, shallow waters of its time. ''Pelagosaurus'' had 30 teeth suitable for hunting and grasping fish,

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s and

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...

s whilst swimming; indeed, one fossil specimen was found with a ''

Leptolepis ''Leptolepis'' (from el, λεπτός , 'slight' and el, λεπίς 'scale') is an extinct genus of stem-teleost fish that lived in what is now Europe during the Jurassic period (Toarcian–Callovian ages). Species The genus ''Leptolepis' ...

''— an early

teleost Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tel ...

fish— in its stomach contents. Its forward-facing eyes and streamlined body suggest that ''Pelagosaurus'' was a

pursuit predator Pursuit predation is a form of predation in which predators actively give chase to their prey, either solitarily or as a group. It is an alternate predation strategy to ambush predation — pursuit predators rely on superior speed, endurance an ...

, rather than a scavenger or ambush hunter. ''Pelagosaurus'' was markedly similar to modern

crocodile Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to inclu ...

s, and would have swum in much similar manner, whipping its tail from side to side, although its veterbral structure was slightly more agile, probably allowing for more movement in the water than its modern equivalents. ''Pelagosaurus'' would have only emerged from the water to lay eggs or to rest on the banks, and would have spent the rest of its day in the water for which it was adapted. Comparisons with other crocodilians shows it was a small prey specialist, less suited to tackle large prey than even modern

gharial The gharial (''Gavialis gangeticus''), also known as gavial or fish-eating crocodile, is a crocodilian in the family Gavialidae and among the longest of all living crocodilians. Mature females are long, and males . Adult males have a distinct b ...

References

{{Taxonbar, from=Q138615 Prehistoric life of Europe Prehistoric pseudosuchian genera Prehistoric marine crocodylomorphs Early Jurassic crocodylomorphs Jurassic reptiles of Europe Thalattosuchians

Discovery

Evolutionary relationships

Palaeobiology

See also

References