Plesiosaur
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? Plesiosaur Conservation status:
Fossil
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Cryptoclididae Elasmosauridae Plesiosauridae Pliosauridae |
Plesiosaurs ( IPA /ˈplisiəˌsɔɹ/) were large, carnivorous aquatic reptiles. They are somewhat fancifully said to look like "a turtle with a snake threaded through its body", though they lacked a shell.
They first appeared in the late Triassic period and thrived until the K-T extinction at the end of the Cretaceous. Despite being large Mesozoic reptiles, they were not a type of dinosaur.
It is occasionally claimed that plesiosaurs are not extinct, although the scientific evidence for this belief is disputed; the modern sightings that are occasionally reported are usually explained as basking shark carcasses or hoaxes.
Description
The typical plesiosaur had a broad body and a short tail. They retained their ancestral two pairs of limbs, which evolved into large flippers. Plesiosaurs evolved from the earlier nothosaurs, who had a more crocodile-like body; major types of plesiosaur are primarily distinguished by head and neck size.
As a group, the plesiosaurs were the largest aquatic animals of their time, and even the smallest were about 2 m (6.5 ft) long. They grew to be considerably larger than the largest giant crocodiles, and were bigger than their successors, the mosasaurs. However, their predecessors as rulers of the sea, the dolphin-like ichthyosaurs, are known to have reached 23 m in length, and the modern whale shark (18 m), sperm whale (20 m), and especially the blue whale (30 m) are known from considerably larger specimens.
The anteriorly placed internal nostrils have palatal grooves to channel water, the flow of which would be maintained by hydrodynamic pressure over the posteriorly placed external nares during locomotion. During its passage through the nasal ducts, the water would have been 'tasted' by olfactory epithelia.
Behavior
Plesiosaurs have been discovered with fossils of belemnites (squid-like animals), and ammonites (giant nautilus-like molluscs) associated with their stomachs. They had powerful jaws, probably strong enough to bite through the hard shells of their prey. The bony fish (Osteichthyes), started to spread in the Jurassic, and were likely prey as well. Recent evidence seems to indicate that some plesiosaurs may have, in fact, been bottom feeders. [1]
It has been theorized that smaller plesiosaurs may have crawled up on a beach to lay their eggs, like the modern leatherback turtle, but it is now clear plesiosaurs gave birth to live young.
Another curiosity is their four-flippered design. No modern animals have this swimming adaptation, so there is considerable speculation about what kind of stroke they used. While the short-necked pliosaurs may have been fast swimmers, the long-necked varieties were built more for maneuverability than for speed. Skeletons have also been discovered with gastroliths in their stomachs, probably to help with buoyancy.
Recent discoveries
In 2002, the "Monster of Aramberri" was announced to the press. Discovered in 1982 at the village of Aramberri, in the Mexican state of Nuevo León, it was originally classified as a dinosaur. The specimen is actually a very large pliosaur, possibly reaching 15 m (50 ft) in length. The media published exaggerated reports claiming it was 25 m (80 ft) long, and weighed up to 150,000 kg, which made it the largest predator of all time. This error was perpetuated in BBC's documentary series Walking with Dinosaurs, which also prematurely classified it as a Liopleurodon ferox.
In 2004, what appears to be a 100 percent intact juvenile plesiosaur was discovered at Bridgwater Bay National Nature Reserve in the United Kingdom, by a local fisherman. The fossil measures 1.5 m (5 ft) in length, and may be related to the Rhomaleosaurus. It is probably the best preserved specimen of a plesiosaur ever discovered.
In fiction
The plesiosaur is popular among children and cryptozoologists, and appears in a number of children's books, and several films. It has appeared in films about lake monsters, including Magic in the Water (1995), and movies about the Loch Ness Monster, such as Loch Ness (1996). In both films, the creature primarily serves as a symbol of a lost, child-like sense of wonder.
Contrary to reports, the long-necked, sharp-toothed creature in the classic film King Kong (1933) — which flips a raft full of rescuers on their way to save Fay Wray, and then munches on 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 sauropod, like the Brontosaurus (now Apatosaurus). However, Kong later battles a serpent-like creature in a cave, which posesses four flippers and resembles a plesiosaur, but acts more like some kind of giant snake. In Steve Alten's novel The Trench, a climatic scene at the end has Angel fighting with several deep sea reptiles similar to Pliosaurs - identified as Kronosaurs.
Contemporary living dinosaurs — myths or truths?
Lake or sea monster sightings are occasionally explained as plesiosaurs. While the survival of a small, unrecorded breeding colony of plesiosaurs for the 65,000,000 years since their apparent extinction is unlikely, the discovery of real and even more ancient living fossils like the Coelacanth, and previously unknown but enormous deep-sea animals like the colossal squid, have fueled imaginations.
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. Members of a blue-ribbon panel of eminent marine scientists in Japan reviewed the discovery. Some of those involved were Professors Ikuo Obata and Hiroshi Ozaki of Japan's National Science Museum and Professor Toshio Kasuya, of Tokyo University's Marine Research Center. These scientists had several things to say about the discovery upon examining the event. Professor Yoshinori Imaizumi of Japan's National Science Museum said, "It's not a fish, whale, or any other mammal." Others have argued that it was actually a decayed basking shark, but Professor Toshio Kasuya said, "If it were a shark, the spine would be smaller… and the neck itself is too long as shown in the picture. I think we can exclude the fish theory." See the external link below for the source article.
The Loch Ness Monster is commonly reported to resemble a plesiosaur, though just as frequently the creature described bears little or no resemblance. In addition, the lake is too cold for a cold-blooded animal to easily survive, air-breathing animals like plesiosaurs would be easily spotted when they surface to breathe, the lake is too small to support a breeding colony, and the loch itself was only formed 10,000 years ago during the last ice age. The sightings can be explained as some combination of waves, floating debris, mist- mirages, swimming animals (like the otter), and hoaxes.
The National Museums of Scotland confirmed that vertebrae discovered on the shores of Loch Ness in 2003 belong to a plesiosaur, though there are some questions about whether the fossils were planted. In any case, the 150,000,000 year-old fossils vastly predate the formation of the loch.