Plesiosaur

Plesiosauria, often known as plesiosaurs, is an extinct Mesozoic marine reptile order related to the Sauropterygia. Plesiosaurs originally appeared around 203 million years ago, possibly in the Rhaetian stage of the Triassic Period. They flourished during the Jurassic Period until the Cretaceous–Paleogene extinction catastrophe at the end of the Cretaceous Period, around 66 million years ago when they vanished. They were found all over the world in the water.

The plesiosaurus were among the first fossil reptiles that were discovered. Scientists recognized their different builds around the turn of the nineteenth century, and they were designated as a separate order in 1835. Plesiosaurus, the eponymous plesiosaurus genus, was named in 1821. More than a hundred genuine species have been described since then. The number of discoveries has grown in the early twenty-first century, leading to a better knowledge of their anatomy, connections, and manner of existence.

There were two morphological types of the plesiosaur dinosaur. In a few species with the "plesiosaur morph '' build, they had extremely long necks and small heads. These types were very slow and fed on small sea animals. Other species, some up to seventeen meters long, had a "pliosaur morph" form with a short neck and a big head; they were apex predators and quick hunters of enormous prey. The two kinds are linked to the Plesiosauroidea's long-necked Plesiosauroidea and Pliosauroidea's short-necked Plesiosauroidea.

The term "plesiosaur" has been used to refer to the Plesiosauria as a whole. It is also sometimes referred only to the long-necked forms which are the old Plesiosauroidea. 

In this article, we are going to discuss the plesiosaur dinosaur, its description, various discoveries related to the plesiosaur, and also a few of the most important facts about the same.

Plesiosaurus Discoveries 

• The first fossils of the extinct reptiles which were recognized were of the skeletal elements of the plesiosaurs. Richard Verstegen of Antwerp showed plesiosaur vertebrae (which he likened to fishes) in his A Restitution of Decayed Intelligence in 1605, which he viewed as proof that Great Britain. In his Lithophylacii Brittannici Ichnographia from 1699, Welshman Edward Lhuyd featured drawings of plesiosaur vertebrae, which were again classified as fish vertebrae or Ichthyospondyli. Other naturalists, like John Woodward, contributed plesiosaur bones to their collections during the seventeenth century and they were only much later recognized as plesiosaurian, and are now partly conserved at the Sedgwick Museum.

• In 1719, the partial skeleton of the plesiosaur was described by William Stukeley. The specimen which was described by William Stukeley is now preserved in the Natural History Museum. It is considered to be an early discovery that is considered to be more or less a complete fossil of the reptile skeleton in a museum collection. The specimen is now referred to as Plesiosaurus dolichodeirus.

• The number of English plesiosaur finds grew dramatically during the eighteenth century, however, they were all more or less fragmented. The reverends William Mounsey and Baptist Noel Turner, both active in the Vale of Belvoir, were considered to be important collectors, and John Nicholls detailed their collections in the first section of his The History and Antiquities of the County of Leicestershire in 1795. One of Turner's fragmentary plesiosaur skeletons is still on display at the British Museum of Natural History and it is now known as Thalassiodracon.

• The name Plesiosaurus was given by Henry De la Beche and William Conybeare in 1821. The first-ever complete skeleton of the Plesiosaurus was discovered by an early paleontologist and a fossil hunter by the name of Mary Anning in December 1823. More fossils of the plesiosaurus were found in the rocks of the Lias group Dorset as time progressed. The name Plesiosaurus was given by Henry De la Beche and William Conybeare in 1821.

• The Plesiosaurus is considered to be one of the first-ever of antediluvian reptiles to be ever discovered and eventually had brought the interest of Victorian England. It was named Plesiosaurus, which translates to near lizard by William Conybeare and Henry De la Beche only to indicate the point that the Plesiosaurus was more like a normal reptile than the Ichthyosaurus. Plesiosaurus is the archetypal Plesiosauria genus and the first to be described, thus giving the order its name. In 1821, Conybeare and De la Beche established the term for a collection of discoveries from Bristol, Dorset, and Lyme Regis. On the basis of Anning's original discoveries, Conybeare identified and described the Plesiosaurus type species, P. dolichodeirus, in 1824.

Description

Plesiosaurs had short tails and large flat bodies. Their arms had developed into four long flippers propelled by powerful muscles linked to large bony plates produced by the shoulder girdle and pelvis. The flippers moved through the water in a flying motion. Plesiosaurs were warm-blooded creatures who breathed air and gave birth to live offspring.

Plesiosaur Size

• The plesiosaur dinosaur varied in length and was between 2 meters to about 15 meters or 50 feet long. The ichthyosaurs, mosasaurids, sharks, and toothed whales in this group were nearly equivalent in size to the biggest ichthyosaurs, mosasaurids, sharks, and toothed whales in the fossil record. Some plesiosaurian fossils, like a 3 meters long pair of heavily rebuilt and fragmented lower jaws from Pliosaurus rossicus which were formerly known as Stretosaurus and Liopleurodon are preserved in the Oxford University Museum and this fossil is around 17 meters tall.

• Many paleontologists have argued that the size or the length cannot alone be enough to determine. As of now only, it is been estimated that the plesiosaur was around 42 feet tall and this is due to the specimen which has been found that is referred to as the Kronosaurus queenslandicus and is believed to be from the early Cretaceous period in Australia. This specimen has an estimated skull length of around 3 meters or 10 feet.

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Dentation and the Skull

• The Plesiosaurus had small heads and the skull is believed to be narrower and long-reaching its greatest width behind its eyes. The anterior portion of the skull is bluntly triangular in nature and in its lateral view, the skull reaches its highest point at the rear of the skull table. 

• The exterior nostrils are higher than the interior nostrils. They are located farther back, nearer the eyes than the tip of the skull, rather than at the tip of the snout. They don't appear to be suited for aquatic olfaction like Rhomaleosaurus' nostrils.

• The eye sockets or the orbits are roughly circular in nature and are positioned around halfway along the length of the skull which is they face up and to the sides. The supratemporal fenestrae, which are about the same size as the orbits and likewise fairly circular, are located just posterior to the orbits. The pineal foramen is located between the four apertures, and a thin sagittal ridge is located between the temporal fenestrae. The pterygoids of the palate are united to the basioccipital of the braincase, as they are in other plesiosaurs, albeit the union is not as strong as in the pliosaurs Rhomaleosaurus and Pliosaurus. There is no suborbital fenestra, and the palatal bones are thin.

• A V shape is formed with an angle of about 45 degrees with the help of the two rami of the lower jaws. The symphysis, the specific area where they meet, is strong. The symphysis joins the two rami, forming a pointed, shallow scoop-like shape. The teeth of the plesiosaur could be described as simple needle-like arms which are curved and circular in the transverse section. These teeth are sharply pointed with striations that run from the tip to the base and are pointed forward. It has been estimated that there are around 25 teeth in the upper jaw and around 24 teeth in the lower jaw.

Vertebral Column 

• Plesiosaurus is considered to be modern-sized plesiosaurs that could grow up to the length of around 4 meters or 11 feet. As it is an extinct animal it is believed that it had 40 cervical vertebrae or the neck vertebrae. Cervical vertebrae (neck vertebrae) number about 40, with various specimens maintaining 38 to 42 cervical vertebrae.   There are a few pectoral vertebrae from the neck-torso transition, about 21 dorsal or back vertebrae, three or more sacral vertebrae, and at least 28 caudal vertebrae in the rest of the vertebral column.

• The cervical vertebrae's centra are often elongated, measuring somewhat longer than tall. In most cases, though, the breadth is larger than or equal to the length. The cervical centres have slightly curved and kidney-shaped articular surfaces with rounded, somewhat rugose borders. On the ventral surface of the central area, small pores termed foramina sub Centralia can be observed. Rugose articular margins can be found on some dorsals, such as the cervicals but however, the caudals lack this characteristic.

• The ribs are found from the neck to the tail. The cervical ribs have two articular heads and are hatchet-shaped. The dorsal ribs on the other hand have only one head and are very thick." Tiny, strong, and pointy or knob-like on both ends," describe the sacral ribs. The morphology of caudal ribs varies depending on where they are on the tail, with anterior instances being pointed and more distal ones being "wide and blunt." Gastralia, or "belly ribs," are also found in Plesiosaurus. Between the shoulder and the pelvis, there are nine or more sets of gastralia. Each set is made up of seven components, which are a midline bone bordered on three sides by three lateral elements.

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Food Resources 

• The food resources of the plesiosaurus have been thought to vary and it all depends on whether they belong to the short-necked plesiosaur morph or the long-necked plesiosaur morph.

• The long neck of the pliosaur morph may have been used to intercept fast-moving fish in pursuit. Plesiosaurs may have alternated between resting on the seafloor and sending their heads out to hunt for food, as evidenced by the fact that their eyes were pointed skyward. Plesiosaurs swam on the surface, allowing their necks to sink to lower levels in search of food. The neck was considered to be highly flexible in all of these interpretations. New explanations have been needed by the current realization that the neck is, in fact, relatively stiff, with little vertical mobility.

• It has been theorized that the length of the neck had made it possible for the plesiosaur to catch the fish. The plesiosaurus hunter visually which means that they used their large eyes and might have used the directional sense of olfaction. Cephalopods, both hard and soft-bodied, were most likely part of their diet. Their jaws were most likely powerful enough to pierce the hard shells of this prey. Cephalopod shells have been discovered in the stomachs of fossil species. Bony fish, which diversified more during the Jurassic, were most likely prey as well. According to an alternative theory, plesiosaur morphs were bottom feeders. The benthos would have been plowed into the seabed by the rigid necks. Long furrows seen in ancient seabeds would have supported this theory.

• It is believed that the Plesiosaur Morphs were not very good enough to catch large and fast-moving prey as their necks were very long which of course helped them to catch many fishes but also had caused enormous skin fiction.

• In their separate food webs, the short-necked plesiosaur morphs were top carnivores or apex predators. They were opportunistic eaters and pursuit or ambush predators of varied-sized food and their teeth could penetrate soft-bodied prey, especially fish. Their heads and jaws were enormous, allowing them to seize and dismember huge creatures. Their morphology allowed them to swim quickly. They, too, hunted by sight.

• Plesiosaurs were food for other predators, as evidenced by bite marks left on a fossilized plesiosaur fin by a shark and the fossilized remains of a mosasaur's stomach contents that are considered to represent the remains of a plesiosaur.

Reproduction 

• The plesiosaurus reptiles are generally oviparous in nature. Until the beginning of the 20the century, it has been believed that smaller plesiosaurs may have crawled up on the beach to lay eggs like the common turtles and that is why they have been related to the reptiles. They crawled and played eggs on the beach all because of their strong limbs and flat undersides.

• By the beginning of the nineteenth century, it was believed or formulated that the plesiosaurs had been viviparous in nature as it was very hard to believe that the largest species at that time which was as big as a whale or even bigger could have survived a beaching.

• The discovery of ichthyosaur embryos in the fossil record revealed that at least one group of aquatic reptiles had produced living young. Harry Govier Seeley was the first to declare that comparable embryos had been discovered in plesiosaurs, reporting in 1887 that he had acquired a cluster with four to eight small skeletons. In 1896, he went into further detail about his discoveries. Plesiosaur embryos, like those of ichthyosaurs, would have been incredibly tiny if they were real. Richard Anthony Thulborn demonstrated in 1982 that Seeley had been duped by a "doctored" crayfish nest fossil.

• At last, an actual specimen was found in 1987 that convincingly proved to everyone that plesiosaurs gave birth to young ones. Similar to contemporary whales, these creatures gave birth to a single big young and likely devoted parental care to their offspring, as evidenced by the fossil of a pregnant Polycotylus latippinus. The juvenile was 1.5 meters long, making it enormous in comparison to its mother, who was five meters long, showing a K-strategy in reproduction. Growth rate and sexual dimorphism if present or not has been yet discovered.