Plesiosaurs

Plesiosaurs (pronounced /ˈpliːziəˌsɔɹ/) (Greek: plesios/πλησιος meaning 'near' or 'close to' and sauros/σαυρος meaning 'lizard') were carnivorous aquatic (mostly marine) reptiles. After their discovery, they were somewhat fancifully said to have resembled "a snake threaded through the shell of a turtle", although they had no shell. The common name 'plesiosaur' is applied both to the 'true' plesiosaurs (Suborder Plesiosauroidea) which includes both long-necked (elasmosaurs) and short-necked (polycotylid) forms and to the larger taxonomic rank of Plesiosauria, which includes the pliosaurs. The pliosaurs were the short-necked, large-headed plesiosaurians that were the apex predators for much of the Mesozoic. There were many species of plesiosaurs, while most of them were not as large as Elasmosaurus.

Plesiosaurs (sensu Plesiosauroidea) appeared at the start of the Jurassic Period and thrived until the K-T extinction, at the end of the Cretaceous Period. While they were Mesozoic reptiles that lived at the same time as dinosaurs, they were not dinosaurs.

History of discovery

The first plesiosaur skeletons were found in England by Mary Anning, in the early 1800s, and were amongst the first fossil vertebrates to be described by science. Many have been found, some of them virtually complete, and new discoveries are made frequently. One of the finest specimens was found in 2002 on the coast of Somerset (England) by someone fishing from the shore. This specimen, called the Collard specimen after its finder, was on display in Taunton museum in 2007. Another, less complete skeleton was also found in 2002, in the cliffs at Filey, Yorkshire, England, by an amateur palaeontologist. The preserved skeleton is displayed at Scarborough Rotunda Museum.

Many museums have plesiosaur specimens. Notable among them is the collection of plesiosaurs in the Natural History Museum, London, which are on display in the marine reptiles gallery. Several historically important specimens can be found there, including the partial skeleton from Nottinghamshire reported by Stukely in 1719 which is the earliest written record of any marine reptile. Others specimens include those purchased from Thomas Hawkins in the early 19th century.

Specimens are on display in museums in the UK, including New Walk Museum, Leicester, The Yorkshire Museum, The Sedgwick Museum in Cambridge, Manchester Museum, Warwick Museum, Bristol Museum and the Dorset Museum. A specimen was put on display in Lincoln Museum in 2005. Peterborough Museum holds an excellent collection of plesiosaur material from the Oxford Clay brick pits in the area. The most complete known specimen of the long-necked plesiosaur Cryptoclidus, excavated in the 1980s can be seen there.

Description

Plesiosaurs had a broad body and a short tail. They retained their ancestral two pairs of limbs, which evolved into large flippers. Plesiosaurs evolved from earlier, similar forms such as pistosaurs or very early, longer-necked pliosaurs. There are a number of families of plesiosaurs, which retain the same general appearance and are distinguished by various specific details. These include the Plesiosauridae, unspecialised types which are limited to the Early Jurassic period; Cryptoclididae, (e.g. Cryptoclidus), with a medium-long neck and somewhat stocky build; Elasmosauridae, with very long, inflexible necks and tiny heads; and the Cimoliasauridae, a poorly known group of small Cretaceous forms. According to traditional classifications, all plesiosaurs have a small head and long neck but, in recent classifications, one short-necked and large-headed Cretaceous group, the Polycotylidae, are included under the Plesiosauroidea, rather than under the traditional Pliosauroidea. Size of different plesiosaurs varied significantly, with an estimated length of Trinacromerum being 3 meters and Mauisaurus growing to 20 meters.

Behaviour

Unlike their pliosaurian cousins, plesiosaurs (with the exception of the Polycotylidae) were probably slow swimmers {Massare, 1988}. It is likely that they cruised slowly below the surface of the water, using their long flexible neck to move their head into position to snap up unwary fish or cephalopods. Their four-flippered swimming adaptation may have given them exceptional maneuverability, so that they could swiftly rotate their bodies as an aid to catching prey.

Contrary to many reconstructions of plesiosaurs, it would have been impossible for them to lift their head and long neck above the surface, in the 'swan-like' pose that is often shown {Everhart, 2005; Henderson, 2006}. Even if they had been able to bend their necks upward to that degree (which they could not), gravity would have tipped their body forward and kept most of the heavy neck in the water.

Taxonomy

The classification of plesiosaurs has varied; the following represents one version (see O'Keefe 2001)

In popular culture

The plesiosaur is popular among children and cryptozoologists, appearing in a number of children's books and several films, including in Jules Verne's novel Journey to the Center of the Earth. However, in Verne's story it is described as being much larger than they were in reality, and shown as having a shell like a turtle. In the bizarre 1899 short story "The Monster of Lake LaMetrie", a man's brain was put into the body of a plesiosaur.

Contrary to reports, the long-necked, sharp-toothed animal in the classic film King Kong (1933), which flips a raft full of rescuers on their way to save Fay Wray, and then devours the swimmers, is not a plesiosaur. Despite striking a profile in the mist very similar to the famous 'Surgeon's Photo' of the Loch Ness Monster, it then chases the routed heroes onto dry land, where it is clearly intended to be a diplodocid sauropod. However, Kong later battles a serpent-like creature in a cave which possesses four flippers, resembles a plesiosaur, but acts more like a giant snake.

Alleged living plesiosaurs

The 1977 discovery of a carcass with flippers and what appeared to be a long neck and head, by the Japanese fishing trawler Zuiyo Maru, off New Zealand, created a plesiosaur craze in Japan. However, the consensus amongst scientists today is that it was a decayed basking shark.

The Loch Ness Monster, and other lake monsters, have been reported to resemble plesiosaurs. The lake plesiosaur theory is considered unlikely for many reasons, including: they are generally too cold for a large cold-blooded animal to survive easily, and that air-breathing animals, like plesiosaurs, would be easily spotted when they surface to breathe. In 2003, the National Museums of Scotland confirmed that vertebrae discovered on the shores of Loch Ness belong to a plesiosaur, but the fossils were deliberately planted (BBC News, July 16, 2003).

Research announced in 2006, by Leslie Noè of the Sedgwick Museum in Cambridge, UK, cast further doubt on the lake plesiosaur theory. While many sightings of the Loch Ness Monster, and similar from around the globe, include reports of it lifting its head out of the water, Noè's study of fossilized vertebrae of Muraenosaurus concluded this articulation would not be possible. Instead, he found that the neck evolved to point downwards allowing the plesiosaur to feed on soft-shelled animals living on the sea floor. ^[1]

Beached carcasses that prove controversial or hard to identify, a phenomenon known as globsters, have fueled the speculation about living plesiosaurs. For example, The Star on April 8, 2006, reported that fishermen discovered bones resembling that of a plesiosaur near Sabah, Malaysia. A team of researchers from Universiti Malaysia Sabah investigated the specimen, but determined the bones were those of a whale^{citation needed}.

Glaciation

The major problem with the hypothesis that plesiosaurs continue to exist in locations such as Loch Ness and Lake Champlain is that these bodies of water were under the most recent continental ice sheets of the last Ice age (USGS Ice Sheets Discription and USGS Glacial References).

Lake Champlain was carved out by the last North American continental glacier, and was not filled with water until 10,000 years ago in subglacial circumstances (Lake Champlain Geology). The same is the case with Loch Ness, as it is a U-shaped valley of glacial origin (Loch Ness Geological History Discussion).

Contents

History of discovery

Description

Behaviour

Taxonomy

In popular culture

Alleged living plesiosaurs

Glaciation

See also

Literature

References

External links

Notes