Plesiosaur

• 1. Introduction

  ›

  In 1832, Professor William Buckland described the plesiosaur as a sea serpent run through a turtle. The phrase stuck because nothing else fit. Here was a Mesozoic marine reptile with a broad flat body, a short tail, and four long flippers that beat through the water like wings. Some had necks so absurdly long, packed with as many as 76 vertebrae, that Icelandic speakers still call them Svaneolur, swan lizards. Others were short-necked giants whose jaws could grab and rip apart large animals. They were among the very first fossil reptiles humans ever recognised as such. Yet for centuries their bones were mistaken for fish, for crocodiles, for drowned sinners from the Great Flood. How did naturalists finally understand a creature that breathed air, bore live young, and may have been warm-blooded? Why did one of these skeletons spark a feud between two American scientists that lasted the rest of their lives? And why, more than 66 million years after the last one vanished, do people still scan the surface of a Scottish lake hoping to glimpse its long neck?

• 2. Bones Mistaken For Fish

  ›

  In 1605, Richard Verstegen of Antwerp printed illustrations of plesiosaur vertebrae in his A Restitution of Decayed Intelligence. He thought they were fish bones, and proof that Britain had once been joined to the European continent. The Welshman Edward Lhuyd repeated the error in his Lithophylacii Brittannici Ichnographia of 1699, again labelling the vertebrae as fish.

  In 1719, William Stukeley described a partial skeleton brought to him by Robert Darwin of Elston, great-grandfather of Charles Darwin. The stone plate came from a quarry at Fulbeck in Lincolnshire. It had been used, fossil-side down, to reinforce the slope of a watering hole at Elston in Nottinghamshire. Once the strange bones were found, the local vicarage displayed them as the remains of a sinner drowned in the Great Flood. Stukeley accepted this diluvial story but guessed it was some sea creature, perhaps a crocodile or a dolphin.

  That specimen now sits in the Natural History Museum under the number NHMUK PV R.1330. It is the earliest more or less complete fossil reptile skeleton held in a museum collection. During the eighteenth century, English finds multiplied, though they stayed fragmentary. The reverends William Mounsey and Baptist Noel Turner collected in the Vale of Belvoir, and John Nicholls described their finds in 1795. One of Turner's partial skeletons survives as specimen NHMUK PV R.45, now referred to Thalassiodracon.

• 3. Naming The Near Reptile

  ›

  In 1821, William Conybeare and Henry Thomas De la Beche examined a partial skeleton in the collection of Colonel Thomas James Birch. They recognised a distinctive group and named a new genus, Plesiosaurus. The name draws on the Ancient Greek plesios, closer to, and a Latinised saurus. It marked the animal as nearer to the Sauria, the crocodile in particular, than the more fish-like Ichthyosaurus. It reads as approaching the Sauria, or near reptile, rather than near lizard.

  In 1823, the commercial fossil collector Mary Anning and her family uncovered an almost complete skeleton at Lyme Regis in Dorset, on what is now called the Jurassic Coast. The Duke of Buckingham acquired it and passed it to the geologist William Buckland. Conybeare described it on the 20th of February 1824, in a paper read at the Geological Society of London. At that same meeting, the first dinosaur was named, Megalosaurus. Conybeare gave the species the name dolichodeirus, meaning longneck.

  The collector Thomas Hawkins brought these animals to the wider public through two lavish books, his Memoirs of Ichthyosauri and Plesiosauri of 1834 and The Book of the Great Sea-Dragons of 1840. Hawkins held a strange view of them, seeing the creatures as monstrous works of the devil from a pre-Adamitic age. He later sold his restored specimens to the British Museum of Natural History.

  Sir Richard Owen alone named nearly a hundred new species, most from isolated bones with too little detail to tell them apart. Many were later invalidated, and Plesiosaurus swelled into a wastebasket taxon. In 1841 Owen named Pliosaurus brachydeirus, the short-necked counterpart to the longneck. The order Plesiosauria itself was named in 1835 by Henri Marie Ducrotay de Blainville.

• 4. The Reversed Spine

  ›

  In 1867, the physician Theophilus Turner found a plesiosaur skeleton near Fort Wallace in Kansas and donated it to Edward Drinker Cope. Cope reconstructed it assuming the longer stretch of vertebral column was the tail. He grew excited, deciding he had found a wholly new group, the Streptosauria or Turned Saurians, marked by reversed vertebrae and a tail that did the swimming.

  When Cope showed off his new Elasmosaurus platyurus, Othniel Charles Marsh suggested a simpler answer. Cope had put the spine on backwards. Cope reacted with indignation. Joseph Leidy quietly took the skull and set it against what Cope called the last tail vertebra. It fitted perfectly, because it was in fact the first neck vertebra, still carrying a piece of the rear skull. Mortified, Cope tried to destroy the entire print run of his textbook, then rushed out a corrected edition bearing the same publication date.

  Marsh later said the affair began their feud, recalling that since then Cope has been my bitter enemy. This single mistake helped open the Bone Wars, the long rivalry in which both men named dozens of plesiosaur genera, most now judged invalid. Around the turn of the century, a former student of Marsh, Samuel Wendell Williston, took over much of the research, publishing his Water reptiles of the past and present in 1914.

• 5. Flying Through The Sea

  ›

  The four-flippered body has driven debate for two centuries over how these animals moved. Sea turtles, the only living animals with four flippers, use just the front pair to swim. Conybeare and Buckland early on compared plesiosaur flippers to bird wings, though flight itself was poorly understood then.

  By the mid nineteenth century, most assumed a rowing stroke, flippers held flat going forward, then turned vertical and pulled back. Such a motion is inefficient. The recovery stroke makes no thrust and the back stroke creates huge turbulence. After bird flight was better understood, Eberhard Fraas in 1905 and Othenio Abel in 1908 proposed a flying motion instead, the flipper tracing an oval and generating thrust on both the down and up strokes.

  In 1924, the first systematic study of plesiosaur muscles, by David Meredith Seares Watson, still concluded they rowed. Watson's rowing model held through the middle of the twentieth century. In 1975, Jane Ann Robinson revived the flying idea, arguing the main muscles were placed for vertical movement and that the joints could not rotate for rowing. She later proposed the ribcage stored energy elastically for an efficient stroke.

  In 1982, Samuel Tarsitano, Eberhard Frey and Jurgen Riess countered that the muscles to lift the limbs were missing or unusable. They offered a flying model with a powerful downstroke and a largely unpowered recovery. In 2010, Frank Sanders and Kenneth Carpenter concluded Robinson had been right, pointing to back muscles like the latissimus dorsi. A 2017 robot study by Luke Muscutt found the rear flippers were actively used, raising propulsive force by 60% and efficiency by 40%.

• 6. Long Necks And Apex Jaws

  ›

  Plesiosaurs split into two body plans that decided how they ate. The long-necked plesiosauromorphs, including the Cryptoclididae, Elasmosauridae and Plesiosauridae, carried small heads on long necks and were relatively slow. The short-necked pliosauromorphs, including the Pliosauridae and Rhomaleosauridae, carried large elongated heads and hunted as apex predators of large prey.

  The long neck has puzzled naturalists from the start. Conybeare offered three uses, to chase fast fish, to send the head out while resting on the bottom, or to plunge the neck down from the surface. Each assumed a flexible neck. Modern work shows the long plate-like spines, the processus spinosi, sharply limited vertical movement, so the neck was rather stiff and could not coil like a serpent. One idea holds the long neck let the head reach a school of fish before the trunk's pressure wave could scatter them. Cephalopod shells have been found in plesiosaur stomachs. Aristonectes carried hundreds of teeth, letting it sieve small crustaceans from the water.

  The short-necked forms were pursuit or ambush hunters with very large heads and teeth built to seize and tear. Their shape allowed high swimming speed. Plesiosaurs were also prey themselves. Shark bite marks survive on a fossil plesiosaur fin, and remains thought to be plesiosaur have turned up in the stomach contents of a mosasaur.

  Many plesiosaurs swallowed gastroliths, stones held in the stomach. A 1949 fossil of Alzadasaurus, later renamed Styxosaurus, held 253 of them. In 1991 an elasmosaurid specimen, KUVP 129744, yielded 47 gastroliths weighing 13 kilograms in total, one of them 17 centimetres across and 1,300 grams. Whether the stones ground food, adjusted buoyancy, or both has never been settled.

• 7. Live Birth And Deep Dives

  ›

  A pregnant fossil found in 1987 finally proved plesiosaurs bore live young. The specimen of Polycotylus latippinus contained a single large juvenile about 1.5 metres long, carried by a mother about five metres long. That ratio points to a K-strategy, few offspring with heavy investment, and probably parental care much like modern whales. Earlier claims had failed. In 1887 Harry Govier Seeley reported a nodule holding tiny skeletons, but in 1982 Richard Anthony Thulborn showed it was a doctored fossil nest of crayfish.

  Decompression sickness left its mark on plesiosaur bones, proving they dived to real depth. The heads of the humeri and femora often show necrosis from too rapid an ascent. The vertebrae escaped this damage, likely protected by a strong blood supply through the foramina subcentralia, paired openings on their undersides. Young plesiosaurs show pachyostosis, very dense bone that may have added weight for descending, while adults have more spongy bone.

  Whether plesiosaurs were warm-blooded is hard to settle. A study in 2010 found fibrolamellar bone, a sign of fast growth, was originally present in sauropterygians. A 2013 paper found basal Pistosauria had it, suggesting the more derived plesiosaurs did too. Isotope work on tooth enamel points to endothermy at lower resting rates, with inferred body temperatures around 26 degrees Celsius. In 2012, a Pliosaurus jaw was described with a joint clearly afflicted by arthritis, a sign of old age.

• 8. The Loch Ness Misunderstanding

  ›

  The belief that plesiosaurs are dinosaurs is a common misconception, yet they sit outside the clade Dinosauria entirely, alongside the ichthyosaurs and mosasaurs. That confusion runs through popular culture. So does the idea that these reptiles might have survived to become lake and sea monsters, a cryptozoological claim the scientific community rejects as fantasy and pseudoscience. Some supposed plesiosaur carcasses have turned out to be partly decomposed basking sharks.

  The Loch Ness monster is often pictured as a plesiosaur, though it is just as often described as something else. The osteology of the neck makes it certain a plesiosaur could not lift its head like a swan above the water, the very pose the monster is said to strike. Air-breathing animals would surface to breathe and be easy to spot. The loch is too small and too poor in food to feed a breeding colony of large animals. And the lake itself formed only about 10,000 years ago at the end of the last ice age, while the youngest plesiosaur fossils are more than 66 million years old.

  The pace of real discovery has only quickened. Through the nineteenth and most of the twentieth century, three or four new genera appeared each decade. The 1990s brought seventeen, and the early twenty-first century named about three or four a year, from new sites in New Zealand, Argentina, Chile, Norway, Japan, China and Morocco. In December 2017, the oldest creature yet found on Antarctica, a large plesiosaur, was recovered from that continent, the first of its kind known there.