Elasmosaurus

Elasmosaurus

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Encyclopedia
Elasmosaurus is a genus
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 plesiosaur
Plesiosaur
Plesiosauroidea is an extinct clade of carnivorous plesiosaur marine reptiles. Plesiosauroids, are known from the Jurassic and Cretaceous Periods...

 with an extremely long neck that lived in the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...

 period (Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...

 stage), 80.5 million years ago.

Description



Elasmosaurus was about 14 m (45.9 ft) in length and weighed over 2000 kg (2.2 ST), making it among the largest plesiosaurs. It differs from all other plesiosaurs by having six teeth per premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....

 (the bones at the tip of the snout) and 71 neck
Cervical vertebrae
In vertebrates, cervical vertebrae are those vertebrae immediately inferior to the skull.Thoracic vertebrae in all mammalian species are defined as those vertebrae that also carry a pair of ribs, and lie caudal to the cervical vertebrae. Further caudally follow the lumbar vertebrae, which also...

 (cervical) vertebrae. The skull was relatively flat, with a number of long pointed teeth. The lower jaws were joined at the tip to a point between the fourth and fifth teeth. The neck vertebrae immediately following the skull were long and low, and had longitudinal lateral crests. Like most elasmosaurids, Elasmosaurus had around three pectoral vertebrae. The tail included at least 18 vertebrae.

The pectoral girdle featured a long bar, not present in juveniles. The scapula
Scapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....

 had margins of approximately equal length for the joint with the coracoid and the articular surface for the upper arm. The anterior
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...

 edge of the pelvic girdle was made up of three almost straight edges directed to the front and sides of the animal. The ischia, a pair of bones that formed the posterior part of the pelvis, were joined along their medial surfaces. The limbs of Elasmosaurus, like those of other plesiosaurs, were modified into approximately equally-sized rigid paddles.

Certain aspects of the anatomy of Elasmosaurus were fairly derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...

 among elasmosaurids, and plesiosaurs in general. As noted, Elasmosaurus can be distinguished by its six premaxillary teeth and 71 cervical vertebrae. Primitively, plesiosaurs and most elasmosaurids had five teeth per premaxilla. Some elasmosaurids had more: Terminonatator
Terminonatator
Terminonatator is a genus of elasmosaurid plesiosaur from the Late Cretaceous of Saskatchewan, Canada. It is known from a skull and partial skeleton from a young adult, found in the Campanian-age Bearpaw Formation near Notukeu Creek in Ponteix...

had nine and Aristonectes
Aristonectes
Aristonectes is an extinct genus of plesiosaur from the Late Cretaceous of what is now South America and Antarctica...

had 10 to 13. In addition, most plesiosaurs had fewer than 60 cervical vertebrae. Aside from Elasmosaurus, plesiosaurs that exceeded 60 cervicals include Styxosaurus
Styxosaurus
Styxosaurus is a genus of plesiosaur of the family Elasmosauridae. Styxosaurus lived during the Santonian and Campanian age of the Cretaceous period.-Etymology:...

, Hydralmosaurus
Hydralmosaurus
Hydralmosaurus is a genus of elasmosaurid plesiosaur. It is known from fossils discovered in Late Cretaceous rocks of Nebraska and Wyoming. Hydralmosaurus was coined as a replacement name for "Elasmosaurus" serpentinus in 1943 by Samuel Paul Welles....

, and Thalassomedon
Thalassomedon
Thalassomedon is a genus of plesiosaur, named by Welles in 1943. Greek, thalassa, "sea" and Greek, medon, "lord, ruler": Sea lord.-Introduction:...

. Elasmosaurus is the only known plesiosaur with more than 70 cervicals. However, it had roughly the same neck length as Thalassomedon because the latter has proportionally longer vertebrae. Elasmosaurus had more vertebrae than any known animal. The presence of the pectoral bar is also considered an advanced feature. The long, low axis
Axis (anatomy)
In anatomy, the second cervical vertebra of the spine is named the axis or epistropheus.It forms the pivot upon which the first cervical vertebra , which carries the head, rotates....

 centrum
Body of vertebra
The body is the largest part of a vertebra, and is more or less cylindrical in shape. For vertebrates other than humans, this structure is usually called a centrum....

 differs from the condition seen in most other plesiosaurs, which have centra that are either shorter in length than height, or about equidimensional. Styxosaurus and Hydralmosaurus also have the condition present in Elasmosaurus. Another unusual feature of Elasmosaurus is the relatively equal lengths of the margins of the scapula, as mentioned above. Most plesiosaurs had longer margins for articulation with the coracoid than for articulation with the upper arm.

Classification and species


While numerous species of Elasmosaurus have been named since its discovery, a 1999 review by Ken Carpenter showed that only one, the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...

 Elasmosaurus platyurus, could be considered valid. Various other species assigned to the genus are either dubious
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...

 or have been classified in other genera. For example, E. serpentinus has been reclassified as Hydralmosaurus
Hydralmosaurus
Hydralmosaurus is a genus of elasmosaurid plesiosaur. It is known from fossils discovered in Late Cretaceous rocks of Nebraska and Wyoming. Hydralmosaurus was coined as a replacement name for "Elasmosaurus" serpentinus in 1943 by Samuel Paul Welles....

, E. morgani as Libonectes
Libonectes
Libonectes is an extinct genus of sauropterygian reptile belonging to the plesiosaur order. It is known from a single fossil specimen found in the Britton Formation of Texas, dated to the lower Turonian stage of the late Cretaceous period.The animal was very similar to the related Thalassomedon,...

, and E. snowii as Styxosaurus
Styxosaurus
Styxosaurus is a genus of plesiosaur of the family Elasmosauridae. Styxosaurus lived during the Santonian and Campanian age of the Cretaceous period.-Etymology:...

. By the early part of the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...

, plesiosaurs have evolved (or have been reduced) into two distinct groups. Elasmosaurus is the type genus
Type genus
In biological classification, a type genus is a representative genus, as with regard to a biological family. The term and concept is used much more often and much more formally in zoology than it is in botany, and the definition is dependent on the nomenclatural Code that applies:* In zoological...

 for one of these groups, the elasmosaurids
Elasmosauridae
Elasmosauridae was the family of plesiosaurs. They had the longest necks of the plesiosaurs and survived from the Late Triassic to the end of the Cretaceous. They had a diet of fish and shelless cephalopods.-Size:...

 which had extremely long necks with relatively short heads, in contrast to the polycotylids which had shorter necks and relatively larger heads. Late Cretaceous elasmosaurids from the Western Interior of North America have few features that separate them and are morphologically primitive
Basal (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:...

. However, as noted above, Elasmosaurus and some others have some derived features. It has been suggested that Elasmosaurus was closely related to Hydralmosaurus and Styxosaurus due to these advanced features.

Discovery


Elasmosaurus platyurus was described in March, 1868 by Edward Drinker Cope
Edward Drinker Cope
Edward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of nineteen...

 from a fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 discovered and collected by Dr. Theophilus Turner, a military doctor, in western Kansas
Kansas
Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...

, USA. Although other specimens of elasmosaurs have been found in various locations in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

, Carpenter (1999) determined that Elasmosaurus platyurus was the only representative of the genus.

When E. D. Cope received the specimen in early March, 1868, he had a pre-conceived idea of what it should look like, and mistakenly placed the head on the wrong end (i.e. the tail). In his defense, at the time he was an expert on lizards, which have a short neck and a long tail, and no one had ever seen a plesiosaur the size of Elasmosaurus. Although popular legend notes that it was Othniel Charles Marsh
Othniel Charles Marsh
Othniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...

 who pointed out the error, there is no factual justification for this account (see below). However, this event is often cited as one of the causes of their long-lasting and acrimonious rivalry, known as the Bone Wars
Bone Wars
The Bone Wars, also known as the "Great Dinosaur Rush", refers to a period of intense fossil speculation and discovery during the Gilded Age of American history, marked by a heated rivalry between Edward Drinker Cope and Othniel Charles Marsh...

. In fact, although Marsh personally collected at least one plesiosaur from Kansas, and had several more from Kansas in the Yale Peabody collection, he never published a single paper on them.

Although Cope verbally announced the discovery of Elasmosaurus platyurus in March 1868, he did not publish the "preprint" of his erroneous reconstruction of Elasmosaurus until August 1869. While much smaller, long-necked plesiosaurs from the Jurassic of England were well known at the time, this was the first time anyone had ever seen a Cretaceous elasmosaur. Cope's reconstruction showed it to have a long sinuous tail like a lizard or a mosasaur
Mosasaur
Mosasaurs are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764...

. Note that while O.C. Marsh claimed to have pointed out Cope's error "20 years after the fact" in an 1890 newspaper article, it was actually Joseph Leidy who pointed out the problem in his Remarks on Elasmosaurus platyurus address at the Academy of Natural Sciences of Philadelphia meeting on March 8, 1870.

Paleobiology



Elasmosaurus fossils have been found in the Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...

-age Upper Cretaceous Pierre Shale
Pierre Shale
The Pierre Shale is a geologic formation or series in the Upper Cretaceous which occurs east of the Rocky Mountains in the Great Plains, from North Dakota to New Mexico....

 of western Kansas. The Pierre Shale represents a period of marine deposition from the Western Interior Seaway
Western Interior Seaway
The Western Interior Seaway, also called the Cretaceous Seaway, the Niobraran Sea, and the North American Inland Sea, was a huge inland sea that split the continent of North America into two halves, Laramidia and Appalachia, during most of the mid- and late-Cretaceous Period...

, a shallow continental sea that submerged much of central North America during the Cretaceous.

Like most plesiosaurs, Elasmosaurus was incapable of raising anything more than its head above the water as it is commonly depicted in art and media. The weight of its long neck placed the center of gravity behind the front flippers. Thus Elasmosaurus could only have raised its head and neck above the water if in shallow water, where it could rest its body on the bottom. The weight of the neck, the limited musculature, and the limited movement between the vertebrae would have prevented Elasmosaurus from raising its head and neck very high as well. Nevertheless one study found that the necks of elasmosaurs were capable of 75–177° of ventral movement, 87–155° of dorsal movement, and 94–176° of lateral movement, depending on the amount of tissue between the vertebrae. "Swan-like" S-shape neck postures which required more than 360° degrees of vertical flexion were not possible. The head and shoulders of the Elasmosaurus most likely acted as a rudder. If the animal moved the anterior part of the body in a certain direction, it would cause the rest of the body to move in that direction. Thus, Elasmosaurus could not have swum in one direction while moving its head and neck either horizontally or vertically in a different direction.

Elasmosaurus was a slow swimmer and may have stalked schools of fish. The long neck would allow Elasmosaurus to conceal itself below the school of fish. It then would have moved its head slowly and approached its prey from below. The eyes of the animal could have had stereoscopic vision, which would help it find small prey. Hunting from below would also have helped by silhouetting the prey in the sunlight while concealing Elasmosaurus in the dark waters below. Elasmosaurus probably ate small bony fish, belemnites (similar to squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...

), and ammonite
Ammonite
Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct subclass within the Molluscan class Cephalopoda which are more closely related to living coleoids Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct...

s (molluscs). It swallowed small stones
Gastrolith
A gastrolith, also called a stomach stone or gizzard stones, is a rock held inside a gastrointestinal tract. Gastroliths are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. The grain size depends upon the size of the animal and the gastrolith's...

 to aid its digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....

. Elasmosaurus is believed to have lived mostly in open ocean. The paddles of Elasmosaurus and other plesiosaurs are so rigid and specialized for swimming that they could not have come on land to lay eggs. Thus it most likely gave live birth to its young like modern sea snakes
Sea Snakes
Sea Snakes were a Canadian indie rock band, formed in 2002 and disbanded in 2005. The band consisted of vocalist and guitarist Jimmy McIntyre, guitarist Kristian Galberg, bassist and saxophonist Jeremy Strachan, keyboardist Shaw-Han Liem and drummer Nathan Lawr.Strachan played in the defunct band...

. While direct evidence of reproduction in Elasmosaurus is not yet known, the contemporaneous plesiosaur Polycotylus
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-cupped vertebrae', referring to the shape of the vertebrae...

is known to have given birth to live young.

General

  • Brown, D. S. "A taxonomic reappraisal of the families Elasmosauridae and Cryptoclididae (Reptilia: Plesiosauroidea)". Révue de Paléobiologie, Volume Spécial, 7, 9-16.
  • Carpenter, K. 1999. "Revision of North American elasmosaurs from the Cretaceous of the western interior". Paludicola 2(2): 148-173.
  • Carpenter, K. 2003. "Vertebrate Biostratigraphy of the Smoky Hill Chalk (Niobrara Formation) and the Sharon Springs Member (Pierre Shale)." High-Resolution Approaches in Stratigraphic Paleontology, 21: 421-437.
  • Cope, E. D. 1868. "Remarks on a new enaliosaurian, Elasmosaurus platyurus." Proceedings of the Academy of Natural Sciences of Philadelphia, 20: 92-93. (for meeting of March 24, 1868
  • Cope, E. D. 1869. "Synopsis of the Extinct Batrachia and Reptilia of North America, Part I". Transactions American Philadelphia Society New Series, 14:1-235, 51 figs., 11 pls. (pre-print dated August, 1869)
  • Everhart, M. J. 2005. Oceans of Kansas - A Natural History of the Western Interior Sea. Indiana University Press, 320 pp.
  • Gasparini, Z. Martin, J. E., and Fernández M. 2003. "The elasmosaurid plesiosaur Aristonectes Cabrera from the latest Cretaceous of South America and Antarctica". Journal of Vertebrate Palaeontology, 23, 104-115.
  • Leidy, J. 1870. "Remarks on Elasmosaurus platyurus". Proceedings of the Academy of Natural Sciences of Philadelphia 22: 9-10.
  • O'Keefe, F. R. and Chiappe, L. M. 2011 "Viviparity and K-selected life history in a Mesozoic marine plesiosaur (Reptilia, Sauropterygia)." Science 333(6044):870–873.
  • Sachs, S. 2004. "Redescription of Woolungasaurus glendowerensis (Plesiosauria: Elasmosauridae) from the. Lower Cretaceous of Northeast Queensland". Memoirs of the Quennsland Museum, 49:215-233
  • Sachs, S. 2005. "Redescription of Elasmosaurus platyurus, Cope 1868 (Plesiosauria: Elasmosauridae) from the Upper Cretaceous (lower Campanian) of Kansas, U.S.A". Paludicola 5(3): 92-106.
  • Sato, Tamaki 2003. "Terminonatator ponteixensis, a new elasmosaur (Reptilia:Sauropterygia) from the Upper Cretaceous of Saskatchewan". Journal of Vertebrate Paleontology 23(1): 89–103.
  • Welles, S. P. 1943. "Elasmosaurid plesiosaurs with descriptions of new material from California and Colorado". Memoirs of the University of California, 13:125-254.
  • Zammit M., Daniels, C. B. and Kear, B. P. 2008. "Elasmosaur (Reptilia: Sauropterygia) neck flexibility: Implications for feeding strategies", Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology 150(2):124-130.

External links