Pelagosaurus
Encyclopedia
Pelagosaurus is an extinct genus
of thalattosuchia
n 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 was markedly similar to the modern-day gharial
, which has similar adaptions and carnivorous feeding habits.
, 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 skull
s and articulated skeleton
s, have been found around Western Europe in locations such as France
and Germany
. 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.
it belongs:
The most recent phylogenetic analyses have all found Pelagosaurus to be a basal teleosaurid, rather than a basal metriorhynchid or thalattosuchian.
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
s and insect
s 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 crocodile
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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of thalattosuchia
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 sometimes colloquially referred to as marine crocodiles or sea crocodiles, though they are not actually members of Crocodilia.The term...
n crocodyliform that lived during the Toarcian
Toarcian
The Toarcian is, in the ICS' geologic timescale, an age or stage in the Early or Lower Jurassic. It spans the time between 183.0 Ma and 175.6 Ma...
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
Western Europe
Western Europe is a loose term for the collection of countries in the western most region of the European continents, though this definition is context-dependent and carries cultural and political connotations. One definition describes Western Europe as a geographic entity—the region lying in the...
. The systematic taxonomy of Pelagosaurus has been fiercely disputed over the years, and was assigned to Thalattosuchia after its systematics within Teleosauridae
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 and were the closest relatives to the Metriorhynchidae, the Mesozoic crocodilians that returned to the sea and evolved...
were disputed. Pelagosaurus was markedly similar to the modern-day gharial
Gharial
The gharial , , also called Indian gavial or gavial, is the only surviving member of the once well-represented family Gavialidae, a long-established group of crocodilians with long, slender snouts...
, which has similar adaptions and carnivorous feeding habits.
Discovery
Pelagosaurus was originally described from a specimen from NormandyNormandy
Normandy is a geographical region corresponding to the former Duchy of Normandy. It is in France.The continental territory covers 30,627 km² and forms the preponderant part of Normandy and roughly 5% of the territory of France. It is divided for administrative purposes into two régions:...
, but the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
for P. typus was discovered north of the town of Ilminster
Ilminster
Ilminster is a country town and civil parish in the countryside of south west Somerset, England, with a population of 4,781. Bypassed a few years ago, the town now lies just east of the intersection of the A303 and the A358...
in Somerset, England. Most Pelagosaurus remains have been found in the Ilminster area, but numerous other remains, predominantly skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
s and articulated skeleton
Skeleton
The skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...
s, have been found around Western Europe in locations such as France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
and Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
. 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
Evolutionary relationships
The evolutionary relationships of Pelagosaurus has been confusing as there have been three different interpretations as to where in ThalattosuchiaThalattosuchia
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 sometimes colloquially referred to as marine crocodiles or sea crocodiles, though they are not actually members of Crocodilia.The term...
it belongs:
- Teleosaurid: The teleosaurid classification of Pelagosaurus, based upon anatomical similarity, was maintained by Eudes-DeslongchampsJacques Amand Eudes-DeslongchampsJacques Amand Eudes-Deslongchamps was a French naturalist and palaeontologist.He was born at Caen in Normandy...
, Westphal and Duffin. - Metriorhynchid: Its position as a basalBasal (phylogenetics)In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
metriorhynchid was made by Buffetaut. - Basal thalattosuchian: However, phylogenetic analyses from the 1980s, 1990s and early 2000s found Pelagosaurus to be the sister taxon to both Teleosauridae and Metriorhynchidae.
The most recent phylogenetic analyses have all found Pelagosaurus to be a basal teleosaurid, rather than a basal metriorhynchid or thalattosuchian.
Palaeobiology
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s and insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s whilst swimming; indeed, one fossil specimen was found with a Leptolepis
Leptolepis
Leptolepis is an extinct genus of teleost fish that lived in the Mesozoic era. It was one of the first teleosts.- Appearance :...
— 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 crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...
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.