Niue 1 Dollar Silver Coin 2013 Life on Earth - Jurassic Period Life Under Water
During the Early Jurassic, animals and plants living both on land and in the seas recovered from one of the largest mass extinctions in Earth history. Many groups of vertebrate and invertebrate organisms important in the modern world made their first appearance during the Jurassic.
Life was especially diverse in the oceans - thriving reef ecosystems, shallow-water invertebrate communities and large swimming predators, including reptiles and squidlike animals. (source: britannica)
Obverse: Effigy of Her Majesty Queen Elizabeth II designed by Raphael Maklouf. On the background planet Earth, shape of continents as during Jurassic periods, as well as fossilized tree-ferns. Inscriptions: "ELIZABETH II" , "NIUE", "ONE DOLLAR", as well as "Ag 925", "2013"and "26.15g" (weight of pure metal).
Reverse: On the background of the sea with crinoids (Saccocoma) plants few animals living in this period: from the left to the right clockwise: Dakosaurus, Megalneusaurus, Plesiosauria and Shonisaurus. Around the coin inscriptions: "LIFE ON EARTH", "JURA", "DINOSAURIA".
Country: Niue.
Year: 2013.
Denomination: 1 NZD - legal tender in New Zealand.
Metal: Silver.
Fineness: 925/1000.
Weight: 26,15 g.
Size: 35,1 x 45,1 mm.
Mintage: 7000.
Quality: Proof.
Jurassic Period
The Jurassic (from Jura Mountains) is a geologic period and system that spans 56.3 million years from the end of the Triassic Period 201.3 million years ago (Mya) to the beginning of the Cretaceous Period 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles. The start of the period is marked by the major Triassic–Jurassic extinction event. Two other extinction events occurred during the period: the Pliensbachian/Toarcian event in the Early Jurassic, and the Tithonian event at the end; however, neither event ranks among the "Big Five" mass extinctions.
The Jurassic is named after the Jura Mountains within the European Alps, where limestone strata from the period were first identified. By the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses, Laurasia to the north and Gondwana to the south. This created more coastlines and shifted the continental climate from dry to humid, and many of the arid deserts of the Triassic were replaced by lush rainforests. On land, the fauna transitioned from the Triassic fauna, dominated by both dinosauromorph and crocodylomorph archosaurs, to one dominated by dinosaurs alone. The first birds also appeared during the Jurassic, having evolved from a branch of theropod dinosaurs. Other major events include the appearance of the earliest lizards, and the evolution of therian mammals, including primitive placentals. Crocodilians made the transition from a terrestrial to an aquatic mode of life. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, while pterosaurs were the dominant flying vertebrates.
Dakosaurus
Dakosaurus is an extinct genus within the family Metriorhynchidae that lived during the Late Jurassic and Early Cretaceous. It was large, with teeth that were serrated and compressed lateromedially (flattened from side to side). The genus was established by Friedrich August von Quenstedt in 1856 for an isolated tooth named Geosaurus maximus by Plieninger. Dakosaurus was a carnivore that spent much, if not all, its life out at sea. The extent of its adaptation to a marine lifestyle means that it is most likely that it mated at sea, but since no eggs or nests have been discovered that have been referred to Dakosaurus, whether it gave birth to live young at sea like dolphins and ichthyosaurs or came ashore like turtles is not known. The name Dakosaurus means "biter lizard", and is derived from the Greek dakos ("biter") and σαῦρος -sauros ("lizard").
Megalneusaurus
Megalneusaurus is an extinct genus of large pliosaur that lived in the Sundance Sea during the Kimmeridgian, ~156-152 million years ago, in the Late Jurassic.
The genus and type species was based upon ribs, vertebrae, a fore-paddle and fragments of the pectoral girdle discovered in Wyoming, USA in 1895. The species named as Megalneusaurus rex (meaning "great swimming lizard King") in 1898. However some of this material has since been lost, although new material has been discovered from the same site. Based upon the bones very large size, it appears to have grown to a size comparable to Liopleurodon.
Material from southern Alaska have been referred to Megalneusaurus, although this material is from an individual of much smaller size.
Megalneusaurus is said to reach lengths of 7.6–9.7 m (25–32 ft), though there are some estimates that propose a length of 11 meters.
Habitat: Megalneusaurus hunted in the warm waters of the Sundance Sea some 150 million years ago. The large, inland sea hosted a wide array of marine reptiles.
Diet: While no stomach contents of Megalneusaurus have been discovered, it is reasonable to assume that it ate medium sized marine reptiles such as the ichthyosaur Ophthalmosaurus, and the cryptocleid plesiosaur, Pantosaurus.
Plesiosauria
The Plesiosauria (Greek: πλησίος, plesios, meaning "near to" and Sauria) or plesiosaurs are an order or clade of Mesozoic marine reptiles (marine Sauropsida), belonging to the Sauropterygia.
Plesiosaurs first appeared in the latest Triassic Period, possibly in the Rhaetian stage, about 203 million years ago. They became especially common during the Jurassic Period, thriving until their disappearance due to the Cretaceous–Paleogene extinction event at the end of the Cretaceous Period, about 66 million years ago. They had a worldwide oceanic distribution.
Plesiosaurs were among the first fossil reptiles discovered. In the beginning of the nineteenth century, scientists realised how distinctive their build was and they were named as a separate order in 1835. The first plesiosaurian genus, the eponymous Plesiosaurus, was named in 1821. Since then, more than a hundred valid species have been described. In the early twenty-first century, the number of discoveries has increased, leading to an improved understanding of their anatomy, relationships and way of life.
Plesiosaurs had a broad flat body and a short tail. Their limbs had evolved into four long flippers, which were powered by strong muscles attached to wide bony plates formed by the shoulder girdle and the pelvis. The flippers made a flying movement through the water. Plesiosaurs breathed air, and bore live young; there are indications that they were warm-blooded.
Plesiosaurs showed two main morphological types. Some species, with the "plesiosauromorph" build, had (sometimes extremely) long necks and small heads; these were relatively slow and caught small sea animals. Other species, some of them reaching a length of up to seventeen metres, had the "pliosauromorph" build with a short neck and a large head; these were apex predators, fast hunters of large prey. The two types are related to the traditional strict division of the Plesiosauria into two suborders, the long-necked Plesiosauroidea and the short-neck Pliosauroidea. Modern research, however, indicates that several "long-necked" groups might have had some short-necked members or vice versa. Therefore, the purely descriptive terms "plesiosauromorph" and "pliosauromorph" have been introduced, which do not imply a direct relationship. "Plesiosauroidea" and "Pliosauroidea" today have a more limited meaning. The term "plesiosaur" is properly used to refer to the Plesiosauria as a whole, but informally it is sometimes meant to indicate only the long-necked forms, the old Plesiosauroidea.
Shonisaurus
Shonisaurus is a genus of ichthyosaur. At least 37 incomplete fossil specimens of the marine reptile have been found in the Luning Formation of Nevada, USA. This formation dates to the late Carnian age of the late Triassic period, about 215 million years ago.
Shonisaurus lived during the Norian stage of the late Triassic period. Shonisaurus popularis measured around 15 metres (49 ft) long. A second species from British Columbia was named Shonisaurus sikanniensis in 2004. Shonisaurus sikkanniensis was one of the largest marine reptiles of all time, measuring 21 metres (69 ft). However, phylogenetic studies later showed Shonisaurus sikanniensis to be a species of Shastasaurus rather than Shonisaurus. A new study, of the year 2013, reassert the original classification, finding it more closely related to Shonisaurus than to Shastasaurus. Specimens belonging to Shonisaurus sikanniensis have been found in the Pardonet Formation British Columbia, dating to the middle Norian age (about 210 million years ago).
Shonisaurus had a long snout, and its flippers were much longer and narrower than in other ichthyosaurs. While Shonisaurus was initially reported to have had socketed teeth (rather than teeth set in a groove as in more advanced forms), these were present only at the jaw tips, and only in the very smallest, juvenile specimens. All of these features suggest that Shonisaurus may be a relatively specialised offshoot of the main ichthyosaur evolutionary line. It was historically depicted with a rather rotund body, but studies of its body shape since the early 1990s have shown that the body was much more slender than traditionally thought. Shonisaurus popularis had a relatively deep body compared with related marine reptiles.
Shonisaurus was also traditionally depicted with a dorsal fin, a feature found in more advanced ichthyosaurs. However, other shastasaurids likely lacked dorsal fins, and there is no evidence to support the presence of such a fin in Shonisaurus. The upper fluke of the tail was probably also much less developed than flukes found in later species.
History
Fossils of Shonisaurus were first found in a large deposit in Nevada in 1920. Thirty years later, they were excavated, uncovering the remains of 37 very large ichthyosaurs. These were named Shonisaurus, which means "lizard from the Shoshone Mountains", after the formation where the fossils were found.
Shonisaurus popularis, was adopted as the state fossil of Nevada in 1984. Excavations, begun in 1954 under the direction of Charles Camp and Samuel Welles of the University of California, Berkeley, were continued by Camp throughout the 1960s. It was named by Charles Camp in 1976.
The Nevada fossil sites can currently be viewed at the Berlin-Ichthyosaur State Park.
