Elasmosaurs
Elasmosauridae
Summary 2
Elasmosaurus (/ɪˌlæzməˈsɔːrəs, -moʊ-/;[1]) is a genus of plesiosaur that lived in North America during the Campanian stage of the Late Cretaceous period, about 80.5 million years ago. The first specimen was discovered in 1867 near Fort Wallace, Kansas, 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 the pectoral and pelvic girdles, and a single species is recognized today; other species are now considered invalid or have been moved to other genera.
Measuring 10.3 meters (34 ft) long, 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 7.1 meters (23 ft) long. Along with its relative Albertonectes, it was one of the longest-necked animals to have lived, with the largest number of neck vertebrae known, 72. 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. Though the only known specimen of Elasmosaurus (specimen ANSP 10081) is fragmentary and missing many elements, related elasmosaurids show it would have had a compact, streamlined body, long, paddle-like limbs, a short tail, a proportionately small head, and an extremely long neck. The neck of Elasmosaurus is estimated at 7.1 meters (23 ft) in length;[2] thus, Elasmosaurus and its relative Albertonectes were some of the longest-necked animals ever to have lived, with the largest number of neck vertebrae of any known vertebrate animals.[3][4] In spite of their many neck vertebrae, the necks of elasmosaurids were less than half as long as those of the longest-necked sauropod dinosaurs.[2] In 1952 the American paleontologist Samuel Welles estimated the body length to have been 10.3 meters (34 ft).[5] In his 1869 description of Elasmosaurus, the American paleontologist Edward Drinker Cope estimated the length of the animal by summing up vertebral lengths and estimations of missing parts, resulting in a total length of 13.1 meters (520 in). The living animal would have been slightly larger due to cartilage present between the vertebral bodies, and was estimated by Cope at roughly 13.7 meters (45 ft).[6] Like other elasmosaurids, Elasmosaurus would have had a slender, triangular skull. The snout was rounded and almost formed a semi-circle when viewed from above, and the premaxillae (which form the front of the upper jaw) bore a low keel at the midline. It is uncertain how many teeth Elasmosaurus had, due to the fragmentary state of the fossils. It probably had six teeth in each premaxilla, and the teeth preserved there were formed like large fangs. The number of premaxillary teeth distinguished Elasmosaurus from primitive plesiosauroids and most other elasmosaurids, which usually had fewer. The two teeth at the front were smaller than the succeeding ones, and were located between the first two teeth in the dentaries of the lower jaws. The known teeth of the front part of the lower jaw were large fangs, and the teeth at the back of the jaws appear to have been smaller. The dentition of elasmosaurids was generally heterodont (irregular throughout the jaws), with the teeth becoming progressively smaller from front to back. The maxillae (largest tooth bearing bone of the upper jaw) of elasmosaurids usually contained 14 teeth, whereas the dentaries (the main part of the lower jaws) usually contained 17 to 19. The teeth interlocked, and their tooth crowns were slender and rounded in cross-section. The mandibular symphysis (where the two halves of the lower jaw connected) was well ossified, with no visible suture.[3][7]
The pectoral and pelvic girdles of the holotype specimen were noted as missing by 1906, but observations about these elements were since made based on the original descriptions and figures from the late 19th century. The shoulder blades (scapulae) were fused and met at the midline, bearing no trace of a median bar. The upper processes of the shoulder blades were very broad, and the "necks" of the shoulder blades were long. The pectoral girdle had a long bar at the middle, a supposedly advanced feature thought to be absent from juvenile plesiosaurs. The ischia (a pair of bones that formed part of the pelvis) were joined at the middle, so that a medial bar was present along the length of the pelvis, a feature usually not found in plesiosaurs.[7] Like other elasmosaurids (and plesiosaurs in general), Elasmosaurus would have had large, paddle-like limbs with very long digits. The paddles at the front (the pectoral paddles) were longer than those at the back (the pelvic paddles).[3]
Fontes e Créditos
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- Adaptado por calgaryzoo de uma obra de (c) Wikipedia, alguns direitos reservados (CC BY-SA), https://en.wikipedia.org/wiki/Elasmosauridae
