Elasmosaurus () is a genus of plesiosaur that lived in North America during the Campanian stage of the Late Cretaceous period, at about 80.6 to 77million years ago. The first specimen was discovered in 1867 near Fort Wallace, Kansas, US, and was sent to the American paleontologist Edward Drinker Cope, who named it E.platyurus in 1868. The generic name means "thin-plate reptile", and the specific name means "flat-tailed". Cope originally reconstructed the skeleton of Elasmosaurus with the skull at the end of the tail, an error which was made light of by the paleontologist Othniel Charles Marsh, and became part of their "Bone Wars" rivalry. Only one incomplete Elasmosaurus skeleton is definitely known, consisting of a fragmentary skull, the spine, and now lost pectoral and pelvic girdles, and a single species is recognized today; other species are now considered invalid or have been moved to other genera. A fragmentary specimen from Germany may belong to this genus.
Measuring in length, Elasmosaurus would have had a streamlined body with paddle-like limbs, a short tail, a small head, and an extremely long neck. The neck alone was around long. Along with its relative Albertonectes, it was one of the longest-necked animals to have lived, with the second largest number of neck vertebrae known, 72, at least 3 fewer than Albertonectes. The skull would have been slender and triangular, with large, fang-like teeth at the front, and smaller teeth towards the back. It had six teeth in each premaxilla of the upper jaw, and may have had 14 teeth in the maxilla and 19 in the dentary of the lower jaw. Most of the neck vertebrae were compressed sideways, and bore a longitudinal crest or keel along the sides.
The family Elasmosauridae was based on the genus Elasmosaurus, the first recognized member of this group of long-necked plesiosaurs. Elasmosaurids were well adapted for aquatic life, and used their flippers for swimming. Contrary to earlier depictions, their necks were not very flexible, and could not be held high above the water surface. It is unknown what their long necks were used for, but they may have had a function in feeding. Elasmosaurids probably ate small fish and marine invertebrates, seizing them with their long teeth, and may have used gastroliths (stomach stones) to help digest their food. Elasmosaurus is known from the Pierre Shale formation, which represents marine deposits from the Western Interior Seaway.
History of study
In early 1867, the American army surgeon Theophilus Hunt Turner and the army scout William "Medecine Bill" Comstock explored the rocks around Fort Wallace, Kansas, where they were stationed during the construction of the Union Pacific Railroad. Approximately northeast of Fort Wallace, near McAllaster, Turner discovered the bones of a large fossil reptile in a ravine in the Pierre Shale formation, and though he had no paleontological experience, he recognized the remains as belonging to an "extinct monster". In June, Turner gave three fossil vertebrae to the American scientist John LeConte, a member of the railway survey, to take back east to be identified. In December, LeConte delivered some of the vertebrae to the American paleontologist Edward Drinker Cope at the Academy of Natural Sciences of Philadelphia (ANSP, known since 2011 as the Academy of Natural Sciences of Drexel University). Recognizing them as the remains of a plesiosaur, larger than any he had seen in Europe, Cope wrote to Turner asking him to deliver the rest of the specimen, at the ANSP's expense.
In December 1867 Turner and others from Fort Wallace returned to the site and recovered much of the vertebral column, as well as concretions that contained other bones; the material had a combined weight of . The fossils were dug or pried out of the relatively soft shale with picks and shovels, loaded on a horse-drawn wagon, and transported back to Fort Wallace. Cope sent instructions on how to pack the bones, which were thereafter sent in hay-padded crates on a military wagon east to the railroad, which had not yet reached the fort. The specimen arrived in Philadelphia by rail in March 1868, whereafter Cope examined it hurriedly; he reported on it at the March ANSP meeting, during which he named it Elasmosaurus platyurus. The generic name Elasmosaurus is a portmanteau of the Ancient Greek (élăsmă, "metal plate") prefixed onto (saûros, "lizard"), in reference to the "plate" bones of the sternal and pelvic regions. However, this name was translated as "thin-plate reptile" in many later works. The specific name also comes from the Ancient Greek (platýs, "flat") and (ourá, "tail"), all meaning "flat-tailed", in reference to the compressed "tail" (actually the neck) and laminae of the vertebrae there.
Cope requested that Turner search for more parts of the Elasmosaurus specimen, and was sent more fossils during August or September 1868. The ANSP thanked Turner for his "very valuable gift" at their meeting in December 1868, and Turner visited the museum during spring, at a time when Cope was absent. Turner died unexpectedly at Fort Wallace on July27, 1869, without seeing the completion of the work he began, but Cope continued to write him, unaware of his death until 1870. The circumstances around Turner's discovery of the type specimen were not covered in Cope's report, and remained unknown until Turner's letters were published in 1987. Elasmosaurus was the first major fossil discovery in Kansas (and the largest from there at the time), and marked the beginning of a fossil collecting rush that sent thousands of fossils from Kansas to prominent museums on the American east coast. Elasmosaurus was one of few plesiosaurs known from the New World at the time, and the first recognized member of the long-necked family of plesiosaurs, the Elasmosauridae.
In 1869 Cope scientifically described and figured Elasmosaurus, and the preprint version of the manuscript contained a reconstruction of the skeleton which he had earlier presented during his report at an ANSP meeting in September 1868. The reconstruction showed Elasmosaurus with a short neck and a long tail, unlike other plesiosaurs, and Cope was also unsure whether it had hind limbs. At an ANSP meeting a year and a half later, in March 1870, the American paleontologist Joseph Leidy (Cope's mentor) noted that Cope's reconstruction of Elasmosaurus showed the skull at the wrong end of the vertebral column, at the end of the tail instead of the neck. Cope had apparently concluded that the tail vertebrae belonged to the neck, since the jaws had been found at that end of the skeleton, even though the opposite end terminated in the axis and atlas bones that are found in the neck. Leidy also concluded that Elasmosaurus was identical to Discosaurus, a plesiosaur he had named in 1851.
To hide his mistake, Cope attempted to recall all copies of the preprint article, and printed a corrected version with a new skeletal reconstruction that placed the head on the neck (though it reversed the orientation of the individual vertebrae) and different wording in 1870. In a reply to Leidy, Cope claimed that he had been misled by the fact that Leidy had arranged the vertebrae of Cimoliasaurus in the reverse order in his 1851 description of that genus, and pointed out that his reconstruction had been corrected. Cope also rejected the idea that Elasmosaurus and Discosaurus were identical, and noted that the latter and Cimoliasaurus did not have any distinguishing features. Though Cope had tried to destroy the preprints, one copy came to the attention of the American paleontologist Othniel Charles Marsh, who made light of the mistake. This led to antagonism between Cope, who was embarrassed by the mistake, and Marsh, who brought up the mistake repeatedly for decades. Marsh returned to the issue during their controversy in the New York Herald in the 1890s (Marsh claimed he had pointed out the error to Cope immediately), when their dispute gained widespread public attention. The argument was part of the "Bone Wars" rivalry between the two, and is well known in the history of paleontology.
Because of Cope's reputation as a brilliant paleontologist, it has been questioned why he would make such an obvious anatomical error. It has been suggested that, as a unique specimen in 1868, the original Elasmosaurus may have been hard to interpret based on the knowledge available at the time. Also, Cope initially thought it consisted of two specimens of different animalsin an 1868 letter to LeConte, Cope had referred to the supposed "smaller specimen" as Discosaurus carinatus. Cope was only in his late twenties and not formally trained in paleontology, and may have been influenced by Leidy's mistake of reversing the vertebral column of Cimoliasaurus. In 2002 the American art historian Jane P. Davidson noted that the fact that other scientists early on had pointed out Leidy's error argues against this explanation, adding that Cope was not convinced he had made a mistake. Plesiosaur anatomy was sufficiently well known at the time that Cope should not have made the mistake, according to Davidson. Cope did little work on the specimen since his 1870 description, and it was kept in storage for nearly 30 years. It was only redescribed in detail in 2005 by the German paleontologist Sven Sachs.
Known and possible fossil elements
Today, the incomplete holotype specimen, cataloged as ANSP 10081, is the only definite specimen of Elasmosaurus. It was long exhibited, but is now stored in a cabinet with other assigned fragments. The specimen consists of the premaxillae, part of the hind-section of the right maxilla, two maxilla fragments with teeth, the front part of the dentaries, three more jaw fragments, the occipital condyle, two cranial fragments of indeterminable identity, 72 cervical vertebrae of the neck, including the atlas and axis, 3pectoral vertebrae, 6back vertebrae, 4sacral vertebrae, 18 tail vertebrae, as well as rib fragments. In 2013 an incomplete neck vertebra centrum of the holotype that had been mentioned by Cope but thought to have been lost was rediscovered in storage by Sachs, and the neck vertebra count was revised from 71 to 72. The neck vertebrae have been taphonomically distorted (changes occurring during decay and fossilization), with some parts being unnaturally compressed or displaced, and some vertebrae are not well prepared. In 1986 a three-dimensional reconstruction of the holotype skeleton was completed and is now displayed at the ANSP. This cast was later copied by the company Triebold Paleontology Incorporated, and replicas were provided to other museums. The replica at the Fort Wallace Museum measures about in length.