Pelagosaurus

Pelagosaurus (meaning "lizard of the open sea") is an extinct genus of thalattosuchian crocodyliform that lived during the Toarcian stage of the Lower Jurassic, around 183 Ma to 175 Ma (million years ago), in shallow epicontinental seas that covered much of what is now Western Europe. The systematic taxonomy of Pelagosaurus has been fiercely disputed over the years, and was assigned to Thalattosuchia after its systematics within Teleosauridae were disputed. Pelagosaurus measured 3 m (10 ft) in length with a weight of 450 kg (1000 lbs), and was markedly similar to the modern-day gharial, which has similar adaptions and carnivorous feeding habits.[2]

Pelagosaurus
Temporal range: 183–176 Ma
Toarcian
Pelagosaurus
Cast of Pelagosaurus typus (skeleton and scutes) at Muséum national d'histoire naturelle, Paris
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Suborder: Thalattosuchia
Genus: Pelagosaurus
Bronn, 1841[1]
Species:
P. typus
Binomial name
Pelagosaurus typus
Bronn, 1841[1]
Synonyms
  • Mosellaesaurus Monard, 1846

Discovery

Pelagosaurus typus
Fossil of Pelagosaurus typus.

Pelagosaurus was originally described from a specimen from Normandy, but the holotype for P. typus was discovered north of the town of Ilminster in Somerset, England. Most Pelagosaurus remains have been found in the Ilminster area, but numerous other remains, predominantly skulls and articulated skeletons, have been found around Western Europe in locations such as France, Germany, and Switzerland. 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.[3]

Evolutionary relationships

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

Pelagosaurus was initially classified as a teleosaurid, based upon anatomical similarity, by Eudes-Deslongchamps, Westphal and Duffin.[4][5][6][7][8]

Its position as a basal metriorhynchid was suggested by Eric Buffetaut in 1980.[9][10]

However, phylogenetic analyses from the 1980s, 1990s and early 2000s found Pelagosaurus to be the sister taxon to both Teleosauridae and Metriorhynchidae.[11][12][13]

The most recent phylogenetic analyses have all found Pelagosaurus to be a basal teleosaurid,[14][15][16] rather than a basal metriorhynchid or thalattosuchian.

Palaeobiology

Pelagosaurus BW
Restoration

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, crustaceans and insects whilst swimming; indeed, one fossil specimen was found with a Leptolepis— an early teleost fish— in its stomach contents. Its forward-facing eyes and streamlined body suggest that Pelagosaurus was a pursuit predator, rather than a scavenger or ambush hunter. Pelagosaurus was markedly similar to modern crocodiles, 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.[3]

See also

References

  1. ^ a b Bronn HG. 1841. Über die fossilen Gaviale der Lias-Formation und der Oolithe. Archiv für Naturgeschichte, Berlin 8:77–82.
  2. ^ https://sites.google.com/site/paleofilescom/pelagosaurus
  3. ^ a b 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.
  4. ^ 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.
  5. ^ Eudes-Deslongchamps EE. 1877. Le Jura Normand, 4. F. Savy (ed). Paris. 60 p.
  6. ^ Westphal F. 1961. "Zur Systematik der deutschen und englischen Lias Krokodilier". Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 113:207–217.
  7. ^ Westphal F. 1962. Die Krokodilen des deutschen und englischen oberen Lias. Palaeontographica, Abteilung A 118:1–96.
  8. ^ Duffin CJ. 1979. "Pelagosaurus (Mesosuchia, Crocodilia) from the English Toarcian (Lower Jurassic)". Neues Jahrbuch für Geologie und Paläontologie, Monatshefte 1979:475–485.
  9. ^ Buffetaut E. 1980. Position systématique et phylogénetique du genre Pelagosaurus Bronn, 1841 (Crocodylia, Mesosuchia), du Toarcian d’Europe. Geobios 13:783–786.
  10. ^ Buffetaut E. 1982. Radiation évolutive, paléoécologie et biogéographie des crocodiliens mésosuchiens. Mémoires de la Sociéte Géologique de France 42:1–88.
  11. ^ 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.
  12. ^ 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.
  13. ^ Buckley GA, Brochu CA, Krause DW, Pol D. 2000. A pugnosed crocodyliform from the Late Cretaceous of Madagascar. Nature 405:941–944.
  14. ^ Mueller-Töwe IJ. 2005. Phylogenetic relationships of the Thalattosuchia. Zitteliana A45: 211–213.
  15. ^ Gasparini Z, Pol D, Spalletti LA. 2006. An unusual marine crocodyliform from the Jurassic-Cretaceous boundary of Patagonia. Science 311: 70-73.
  16. ^ Young MT. 2007. The evolution and interrelationships of Metriorhynchidae (Crocodyliformes, Thalattosuchia). Journal of Vertebrate Paleontology 27 (3): 170A.
Aegyptosuchidae

Aegyptosuchidae is an extinct family of eusuchian crocodyliforms from the Cretaceous period of Africa. They are characterized by their large size and flat heads. The family includes two genera, Aegyptosuchus and Aegisuchus.

Anthracosuchus

Anthracosuchus (meaning "coal crocodile" in Greek) is an extinct genus of dyrosaurid crocodyliform from the Paleocene of Colombia. Remains of Anthracosuchus balrogus, the only known species, come from the Cerrejón Formation in the Cerrejón mine, and include four fossil specimens with partial skulls. Anthracosuchus differs from other dyrosaurids in having an extremely short (brevirostrine) snout, widely spaced eye sockets with bony protuberances around them, and osteoderms that are smooth and thick. It is one of the most basal dyrosaurids along with Chenanisuchus and Cerrejonisuchus. The species name is a reference to the Balrog, a creature in J. R. R. Tolkien's fantasy novel The Lord of the Rings that could, like the remains of Anthracosuchus, be found in a mine.

Atoposauridae

Atoposauridae is a family of crocodile-line archosaurs belonging to Neosuchia. The majority of the family are known from Late Jurassic to Early Cretaceous marine deposits in France, Portugal, and Bavaria in southern Germany. The discovery of the genus Aprosuchus, however, extends the duration of the lineage to the end of the Cretaceous in Romania.

Brillanceausuchus

Brillanceausuchus is an extinct genus of atoposaurid crocodylomorph. Fossils have been found in Early Cretaceous–age rocks of Cameroon. The genus is notable for the position of the secondary choana within its palate. Parts of the pterygoid bones make up the rostral margin of the choana and thus separate it from the palatines, a feature also seen in the more advanced neosuchian suborder Eusuchia. This characteristic was once thought to be characteristic of Eusuchia, but its presence in Brillanceausuchus suggests that the trait is homoplasic, thus making the evolution of the position of the choana within crocodilians more complex than previously thought.

Coelosuchus

Coelosuchus is an extinct genus of goniopholidid mesoeucrocodylian. Fossils have been found from the Graneros Shale of the Benton Group in Wyoming, and are of Cenomanian age. It was slightly over 1 meter in length.

Eusuchia

The Eusuchia ("true crocodiles") are a clade of crocodylomorphs that first appears in the Early Cretaceous with Hylaeochampsa. Along with Dyrosauridae and Sebecosuchia, they were the only crocodyliformes who survived the K-T extinction. Since the other two clades died out 35 and 11 million years ago, all living crocodilian species are eusuchians, as are many extinct forms.

Karatausuchus

Karatausuchus is an extinct genus of atoposaurid crocodylomorph. It is known from a single specimen discovered in the Late Jurassic (Oxfordian - Kimmeridgian) Karabastau Svita from the vicinity of Mikhailovka in the Karatau Mountains of southern Kazakhstan. The type specimen is PIN 25858/1, a complete but poorly preserved juvenile skeleton with some possible soft tissue preservation. It is notable for having over 90 teeth, but its other anatomical details are difficult to discern. The length of this individual is estimated at 160 millimetres (6.3 in). Karatausuchus was described in 1976 by Mikhail Efimov, and the type species is K. sharovi.

Laganosuchus

Laganosuchus is an extinct genus of stomatosuchid crocodyliform. Fossils have been found from Niger and Morocco and date back to the Upper Cretaceous.

Leptolepis

Leptolepis ("delicate scale") is an extinct genus of teleost fish that lived in freshwater and marine environments from the Middle Triassic period until the Early Cretaceous. The genus is one of the earliest recognized teleost genera.

Nannosuchus

Nannosuchus (meaning "dwarf crocodile") is an extinct genus of goniopholidid mesoeucrocodylian from the Berriasian of England.

Neosuchia

Neosuchia is a clade within Mesoeucrocodylia that includes all modern extant crocodilians and their closest fossil relatives. It is defined as the most inclusive clade containing all crocodylomorphs more closely related to Crocodylus niloticus (the Nile Crocodile) than to Notosuchus terrestris. Neosuchia is very diverse and may be polyphyletic, as the clade has undergone many revisions since it was first named in 1988. Neosuchians first appear in the Early Jurassic with the earliest known goniopholid Calsoyasuchus, which lived during the Sinemurian and Pliensbachian stages.

Pholidosaurus

Pholidosaurus is an extinct genus of neosuchian crocodylomorph. It is the type genus of the family Pholidosauridae. Fossils have been found in northwestern Germany. The genus is known to have existed during the Berriasian stage of the Early Cretaceous. Fossil material found from the Annero and Jydegård Formations in Skåne, Sweden and on the island of Bornholm, Denmark, have been referred to as a mesoeucrocodylian, and possibly represent the genus Pholidosaurus.

Shamosuchus

Shamosuchus is an extinct genus of neosuchian crocodile that lived during the Late Cretaceous (Santonian-Campanian) period in what is now the Gobi desert of Mongolia, approximately 85 to 74 million years ago.

Symptosuchus

Symptosuchus is an extinct genus of goniopholidid mesoeucrocodylian. It is known from the Late Cretaceous of Argentina. Argentine paleontologist Florentino Ameghino named the genus in 1899, along with the type species S. contortidens. It was formally described by Carlos Rusconi in 1934.

Teleosauridae

The teleosaurids were marine crocodyliforms similar to the modern gharial that lived from the Early Jurassic to the Early Cretaceous. They had long snouts, indicative of piscivory (fish eating) and were the closest relatives to the Metriorhynchidae, the Mesozoic crocodilians that returned to the sea and evolved paddle-like forelimbs and a shark-like tail.

Thalattosuchia

Thalattosuchia is the name given to 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 Crocodilia.

The term Thalattosuchia was coined by Fraas in 1901. Various authors considered Thalattosuchia an infraorder or a suborder within "Mesosuchia". However, the term "Mesosuchia" is a paraphyletic group, and as such is no longer used. For consistency, the Thalattosuchia are here placed at suborder rank, although the order that contains it is unnamed.

Since Buffetaut (1982) demonstrated the shared characteristics of the early forms of Metriorhynchidae and Teleosauridae, Thalattosuchia has consisted of these two families.Some of the early members of Teleosauridae have been discovered in non-marine deposits. The systematics of the genus Pelagosaurus are confused, with differencing topologies placing it as either a teleosaurid, or as the sister taxon to a Teleosauridae + Metriorhynchidae clade. Others considered Pelagosaurus to be a basal metriorhynchid.

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 age began with the Toarcian turnover, the extinction event that sets its fossil faunas apart from the previous Pliensbachian age.

Wahasuchus

Wahasuchus is a genus of extinct mesoeucrocodylian of the Middle Campanian age found in the Quseir Formation, Egypt. The generic name derives from the Arabic word واحة (waha), which means "oasis", and souchos from the Greek in honor of crocodile-headed god of ancient Egypt. The specific egyptensis (Lat.) means from Egypt.Fossils of skull and jaw fragments, dorsal vertebrae, and fragmentary appendicular remains have been recovered.

Teleosauridae
Metriorhynchoidea
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