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Plesiosauroidea (;
Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...
: 'near, close to' and 'lizard') is an
extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
of
carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose nutrition and energy requirements are met by consumption of animal tissues (mainly mu ...
marine
reptiles Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...
. They have the
snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...
-like longest neck to body ratio of any reptile. Plesiosauroids are known from the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...
and
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
periods. After their discovery, some plesiosauroids were said to have resembled "a snake threaded through the shell of a turtle", although they had no shell. Plesiosauroidea appeared at the
Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassicâ ...
Period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...
(late
Sinemurian In the geologic timescale, the Sinemurian is an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic epoch (geology), Epoch or series (stratigraphy), Series. It spans the time between 199.5 ±0.3 annu ...
stage) and thrived until the K-Pg extinction, at the end of the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
Period. The oldest confirmed plesiosauroid is ''
Plesiosaurus ''Plesiosaurus'' (Greek: ' ('), near to + ' ('), lizard) is a genus of extinct, large marine sauropterygian reptile that lived during the Early Jurassic. It is known by nearly complete skeletons from the Lias of England. It is distinguishable by ...
'' itself, as all younger taxa were recently found to be pliosauroids. While they were
Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...
diapsid Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The earliest traditionally identified diapsids, the araeosc ...
reptiles that lived at the same time as dinosaurs, they did not belong to the latter.
Gastrolith A gastrolith, also called a stomach stone or gizzard stone, is a rock held inside a gastrointestinal tract. Gastroliths in some species are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. In ...
s are frequently found associated with plesiosaurs.


History of discovery

The first complete plesiosauroid skeletons were found in England by
Mary Anning Mary Anning (21 May 1799 â€“ 9 March 1847) was an English fossil collector, fossil trade, dealer, and palaeontologist. She became known internationally for her discoveries in Jurassic marine fossil beds in the cliffs along the English Cha ...
, in the early 19th century, and were amongst the first fossil vertebrates to be described by science. Plesiosauroid remains were found by the Scottish geologist
Hugh Miller Hugh Miller (10 October 1802 – 23/24 December 1856) was a Scottish geologist, writer and folklorist. Life and work Miller was born in Cromarty, the first of three children of Harriet Wright (''bap''. 1780, ''d''. 1863) and Hugh Miller ...
in 1844 in the rocks of the Great Estuarine Group (then known as 'Series') of western Scotland. Many others have been found, some of them virtually complete, and new discoveries are made frequently. One of the finest specimens was found in 2002 on the coast of
Somerset Somerset ( , ), Archaism, archaically Somersetshire ( , , ) is a Ceremonial counties of England, ceremonial county in South West England. It is bordered by the Bristol Channel, Gloucestershire, and Bristol to the north, Wiltshire to the east ...
(England) by someone fishing from the shore. This specimen, called the Collard specimen after its finder, was on display in Taunton Museum in 2007. Another, less complete, skeleton was also found in 2002, in the cliffs at
Filey Filey () is a seaside town and civil parishes in England, civil parish in North Yorkshire, England. It is located between Scarborough, North Yorkshire, Scarborough and Bridlington on Filey Bay. Although it was a fishing village, it has a large ...
, Yorkshire, England, by an amateur palaeontologist. The preserved skeleton is displayed at
Rotunda Museum The Rotunda Museum is one of the oldest purpose-built museums still in use in the United Kingdom. The curved grade II* listed building was constructed in 1829 as one of the country's first purpose-built museums. Situated in the English coasta ...
in Scarborough.


Description

Plesiosauroids had a broad body and a short
tail The tail is the elongated section at the rear end of a bilaterian animal's body; in general, the term refers to a distinct, flexible appendage extending backwards from the midline of the torso. In vertebrate animals that evolution, evolved to los ...
. They retained their ancestral two pairs of limbs, which evolved into large flippers. It has been determined by teeth records that several sea-dwelling reptiles, including plesiosauroids, had a warm-blooded metabolism similar to that of mammals. They could generate
endothermic An endothermic process is a chemical or physical process that absorbs heat from its surroundings. In terms of thermodynamics, it is a thermodynamic process with an increase in the enthalpy (or internal energy ) of the system.Oxtoby, D. W; Gillis, ...
heat to survive in colder habitats.


Evolution

Plesiosauroids evolved from earlier, similar forms such as
pistosaurs Pistosauroidea is a group of marine reptiles within the superorder Sauropterygia that first appeared in the latter part of the Early Triassic and were the ancestors of plesiosaurs. Pistosauroids are rare in Triassic marine assemblages, and are re ...
. There are a number of
families Family (from ) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictability, structure, and safety as ...
of plesiosauroids, which retain the same general appearance and are distinguished by various specific details. These include the
Plesiosauridae The Plesiosauridae are a monophyletic family (biology), family of plesiosaurs named by John Edward Gray in 1825.Ketchum, H. F., and Benson, R. B. J., 2010. "Global interrelationships of Plesiosauria (Reptilia, Sauropterygia) and the pivotal role ...
, unspecialized types which are limited to the
Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassicâ ...
period;
Cryptoclididae Cryptoclididae is a family of medium-sized plesiosaurs that existed from the Middle Jurassic to the Early Cretaceous. They had long necks, broad and short skulls and densely packed teeth. They fed on small soft-bodied preys such as small fish and ...
, (e.g. ''
Cryptoclidus ''Cryptoclidus'' ( ) is a genus of plesiosaur reptile from the Middle Jurassic Period (geology), period of England, France, and Cuba. Discovery ''Cryptoclidus'' was a plesiosaur whose specimens include adult and juvenile skeletons, and rema ...
''), with a medium-long neck and somewhat stocky build;
Elasmosauridae Elasmosauridae, often called elasmosaurs or elasmosaurids, is an extinct family of plesiosaurs that lived from the Hauterivian stage of the Early Cretaceous to the Maastrichtian stage of the Late Cretaceous period (c. 130 to 66 mya). The taxo ...
, with very long, flexible necks and tiny heads; and the
Cimoliasauridae Elasmosauridae, often called elasmosaurs or elasmosaurids, is an extinct family of plesiosaurs that lived from the Hauterivian stage of the Early Cretaceous to the Maastrichtian stage of the Late Cretaceous period (c. 130 to 66 mya). The taxon ...
, a poorly known group of small Cretaceous forms. According to traditional classifications, all plesiosauroids have a small head and long neck but, in recent classifications, one short-necked and large-headed Cretaceous group, the
Polycotylidae Polycotylidae is a family of plesiosaurs from the Cretaceous, a sister group to Leptocleididae. They are known as false pliosaurs. Polycotylids first appeared during the Albian stage of the Early Cretaceous, before becoming abundant and widesprea ...
, are included under the Plesiosauroidea, rather than under the traditional Pliosauroidea. Size of different plesiosaurs varied significantly, with an estimated length of ''
Trinacromerum ''Trinacromerum'' is an extinct genus of sauropterygian reptile, a member of the polycotylid plesiosaurs. It contains two species, ''T. bentonianum'' and ''T. kirki''. Specimens have been discovered in the Late Cretaceous fossil deposits of what ...
'' being three meters and ''
Mauisaurus ''Mauisaurus'' ("Māui lizard") is a dubious genus of plesiosaur that lived during the Late Cretaceous period in what is now New Zealand. Numerous specimens have been attributed to this genus in the past, but a 2017 paper restricts ''Mauisaurus' ...
'' growing to twenty meters.


Relationships

Within Plesiosauroidea, there is a more exclusive group, Cryptoclidia. Cryptoclidia was named and defined as a node clade in 2010 by
Hilary Ketchum Hilary or Hillary may refer to: * Hilary (name), or Hilarie or Hillary, a given name and surname ** Hillary Clinton, American politician ** Edmund Hillary, one of the first to summit Mount Everest * Hillary Coast, Antarctica * Hilary term, the spr ...
and Roger Benson: the group consisting of the
last common ancestor A most recent common ancestor (MRCA), also known as a last common ancestor (LCA), is the most recent individual from which all organisms of a set are inferred to have descended. The most recent common ancestor of a higher taxon is generally assu ...
of ''
Cryptoclidus ''Cryptoclidus'' ( ) is a genus of plesiosaur reptile from the Middle Jurassic Period (geology), period of England, France, and Cuba. Discovery ''Cryptoclidus'' was a plesiosaur whose specimens include adult and juvenile skeletons, and rema ...
eurymerus'' and ''
Polycotylus ''Polycotylus'' is a genus of plesiosaur within the family Polycotylidae. The type species is ''P. latippinis'' and was named by American paleontologist Edward Drinker Cope in 1869. Eleven other species have been identified. The name means 'much- ...
latipinnis''; and all its descendants. The smaller group within Cryptoclidia was erected prior, in 2007 under the name "Leptocleidoidea". Although established as a clade, the name Leptocleidoidea implies that it is a
superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...
. Leptocleidoidea is placed within the superfamily Plesiosauroidea, so it was renamed Leptocleidia by Hilary F. Ketchum and Roger B. J. Benson (2010) to avoid confusion with ranks. Leptocleidia is a
node-based taxon Phylogenetic nomenclature is a method of nomenclature for taxon, taxa in biology that uses phylogenetics, phylogenetic definitions for taxon names as explained below. This contrasts with Biological classification, the traditional method, by which ...
which was defined by Ketchum and Benson as "''
Leptocleidus superstes ''Leptocleidus'' is an extinct genus of plesiosaur, belonging to the family Leptocleididae.Smith AS, Dyke GJ. 2008. The skull of the giant predatory pliosaur ''Rhomaleosaurus cramptoni'': implications for plesiosaur phylogenetics. ''Naturwissensc ...
'', ''
Polycotylus latipinnis ''Polycotylus'' is a genus of plesiosaur within the family Polycotylidae. The type species is ''P. latippinis'' and was named by American paleontologist Edward Drinker Cope in 1869. Eleven other species have been identified. The name means 'much- ...
'', their most recent common ancestor and all of its descendants". The following
cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
follows an analysis by Benson & Druckenmiller (2014).


Behavior

Unlike their pliosauroid cousins, plesiosauroids (with the exception of the Polycotylidae) were probably slow swimmers. It is likely that they cruised slowly below the surface of the water, using their long flexible neck to move their head into position to snap up unwary fish or
cephalopods A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...
. Their four-flippered swimming adaptation may have given them exceptional maneuverability, so that they could swiftly rotate their bodies as an aid to catching prey. Contrary to many reconstructions of plesiosauroids, it would have been impossible for them to lift their head and long neck above the surface, in the "
swan Swans are birds of the genus ''Cygnus'' within the family Anatidae. The swans' closest relatives include the goose, geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe (biology) ...
-like" pose that is often shown. Even if they had been able to bend their necks upward to that degree (which they could not), gravity would have tipped their body forward and kept most of the heavy neck in the water. On 12 August 2011, researchers from the U.S. described a fossil of a pregnant plesiosaur found on a Kansas ranch in 1987. The plesiosauroid, ''Polycotylus latippinus'', has confirmed that these predatory marine reptiles gave birth to single, large, live offspring—contrary to other marine reptile reproduction which typically involves a large number of small babies. Before this study, plesiosauroids had sometimes been portrayed crawling out of water to lay eggs in the manner of sea turtles, but experts had long suspected that their anatomy was not compatible with movement on land. The adult plesiosaur measures long and the juvenile is long.


References


Sources

* *Carpenter, K. 1997. "Comparative cranial anatomy of two North American Cretaceous plesiosaurs". Pp. 91–216, in Calloway J. M. and E. L. Nicholls, (eds.), ''Ancient Marine Reptiles'', Academic Press, San Diego. * * * *Ellis, R. 2003. ''Sea Dragons ( Kansas University Press) * * * * *Everhart, M. J. 2005. "Where the Elasmosaurs roamed", Chapter 7 in ''Oceans of Kansas: A Natural History of the Western Interior Sea'',
Indiana University Press Indiana University Press, also known as IU Press, is an academic publisher founded in 1950 at Indiana University that specializes in the humanities and social sciences. Its headquarters are located in Bloomington, Indiana. IU Press publishes ...
, Bloomington, 322 p. *Everhart, M. J. 2005. "Gastroliths associated with plesiosaur remains in the Sharon Springs Member (Late Cretaceous) of the Pierre Shale, Western Kansas"
on-line, updated from article in ''Kansas Acad. Sci. Trans.'' 103(1-2):58-69
* * * * *Everhart, M. J. 2007. Sea Monsters: Prehistoric Creatures of the Deep. National Geographic, 192 p. . *Everhart, M. J

and scans o

*Hampe, O., 1992: ''Courier Forsch.-Inst. Senckenberg'' 145: 1-32. * * * *Massare, J. A. 1994. Swimming capabilities of Mesozoic marine reptiles: a review. pp. 133–149 In Maddock, L., Bone, Q., and Rayner, J. M. V. (eds.), Mechanics and Physiology of Animal Swimming, Cambridge University Press. *Smith, A. S. 2008. Fossils explained 54: plesiosaurs. Geology Today. 24, (2), 71-7
PDF document on ''the Plesiosaur Directory''
*Storrs, G. W., 1999. An examination of Plesiosauria (Diapsida: Sauropterygia) from the Niobrara Chalk (Upper Cretaceous) of central North America, University of Kansas Paleontological Contributions, (N.S.), No. 11, 15 pp. *Welles, S. P. 1943. Elasmosaurid plesiosaurs with a description of the new material from California and Colorado. University of California Memoirs 13:125-254. figs. 1-37., pls. 12–29. *Welles, S. P. 1952. A review of the North American Cretaceous elasmosaurs. University of California Publications in Geological Science 29:46-144, figs. 1-25. *Welles, S. P. 1962. A new species of elasmosaur from the Aptian of Columbia and a review of the Cretaceous plesiosaurs. University of California Publications in Geological Science 46, 96 pp. * *, 2 fig. *Williston, S. W. 1902. Restoration of ''Dolichorhynchops osborni'', a new Cretaceous plesiosaur. Kansas University Science Bulletin, 1(9):241-244, 1 plate. *Williston, S. W. 1903. North American plesiosaurs. Field Columbian Museum, Publication 73, Geology Series 2(1): 1-79, 29 pl. *, 4 pl. * * ( ), 1997: in ''Reports of the National Center for Science Education'', 17.3 (May/June 1997) pp 16–28.


External links


Fox News: Possibly Complete Plesiosaur Skeleton Found in Arctic
*
The Plesiosaur Site
'. Richard Forrest. *
The Plesiosaur Directory
'. Dr Adam Stuart Smith. *
The name game: plesiosaur-ia, -oidea, -idae, or -us?
'. *

'. Mike Everhart. *

'. Mike Everhart. *
Triassic reptiles had live young
'
The Filey (Yorkshire) Plesiosaur 2002 (part 1)The Filey (Yorkshire) Plesiosaur 2002 (part 2)

Antarctic Researchers to Discuss Difficult Recovery of Unique Juvenile Plesiosaur Fossil
from the National Science Foundation, December 6, 2006. *

. Allan Hall and Mark Henderson. ''Times Online'', December 30, 2002. (Monster of Aramberri) {{Taxonbar, from=Q1619550 Plesiosaurs Taxa named by John Edward Gray Pliensbachian first appearances Maastrichtian extinctions