Dinosauria Caspakensis: Plesiosaurus olsoni

The Burroughs master illustrator J. Allen St. John's illustration of P. olsoni

Close by us something rose to the surface of the river and dashed at the periscope. I had a vision of wide, distended jaws, and then all was blotted out...
  - Chapter 4, "The Land That Time Forgot," Edgar Rice Burroughs, 1918

The first native of Caspak the reader encounters is, alas, not technically a dinosaur, though it is one of another ruling dynasty of the Mesozoic - a Plesiosaurus ("near lizard"). "The Land That Time Forgot" is not the first story to feature a Plesiosaurus, but as far as I can tell, it is the first to do battle with a German submarine, which earns it a special place in the annals of Man vs. Dinosaur.

Discovery of the Plesiosaurus

Henry de la Beche's "Duria Antiquior, A More Ancient Dorset" is one of the earliest examples of paleoart. The reconstructions of the Ichthyosaurus and Plesiosaurus came only ten years after their first scientific descriptions.

Then again something charged the periscope and blotted out the mirror. I will confess that I was almost gasping for breath as I gave the commands to emerge. Into what sort of strange land had fate guided us?
 - Chapter 4, "The Land That Time Forgot," Edgar Rice Burroughs, 1918

Although the science of palaeontology is comparatively modern, humans have happened upon ancient bones, skulls, teeth, claws, and eggs for as long as humans have existed. Adrienne Mayor's The First Fossil Hunters details many proto-palaeontologists who find the bones of "dragons," "cyclopes," and "griffins." Another book by the same author, Fossil Legends of the First Americans, correlates legends of "water monsters" among the Cheyenne People with the plentiful Jurassic marine fossils of midwestern North America.

Mayor's argument that these fossils may have been the inspiration for creatures and monsters of mythology has historical precedent:

The curious connection between the superstitions of races, the traditionary tales of remote tribes, and the developments of the truths of science, are often of a very marked character, and they cannot but be regarded as instructive. In the wonders of “olden time” fiction has ever delighted; and a thousand pictures have been produced of a period when beings lived and breathed upon the earth which have no existence now. 

Hydras, harpies, and sea-monsters, figure in the myths of antiquity. In the mythology of the northern races of Europe we have fiery flying dragons, and Poetry has placed these as the guardians of the “hoarded spirit” and protectors of the enchanted gold. 

Through the whole of the romance period of European literature, nothing figures but serpents, “white and red,” toiling and fighting underground,—thus producing earthquakes, as in the story of Merlin and the building of Stonehenge. Flying monsters, griffins and others, which now live only in the meaningless embellishments of heraldry, appear to have been conceived by the earlier races of men as the representatives of power. Curious is it, too, to find the same class of ideas prevailing in the East. The monster dragons of the Chinese, blazoned on their standards and ornamenting their temples; - the Buddaical superstition that the world is supported on a vast elephant, which stands on the back of a tortoise, which again rests on a serpent, whose movements produce earthquakes and violent convulsions; - the rude decorations also of the temples of the Aztecs, which have been so recently restored to our knowledge by the adventurous travellers of Central America, - all give expression to the same mythological idea. 

Do not these indicate a faint and shadowy knowledge of a previous state of organic existence? The process of communion between man of the present, and the creations of a former world, we know not; it is mysterious, and for ever lost to us. But even the most ignorant and uncultivated races of mankind have figured for themselves the images of creatures which, whilst they do really bear some resemblance to things which have for ever passed away, do not, in the remotest degree, partake of any of the peculiarities of existing creations. 

The ichthyosaurus, and the plesiosaurus, and the pterodactylus, are preserved in the rude images of harpies, of dragons, and of griffins; and, although the idea of an elephant standing on the back of a tortoise was often laughed at as an absurdity, Captain Cautley and Dr. Falconer at length discovered in the hills of Asia the remains of a tortoise in a fossil state of such a size that an elephant could easily have performed the feat.

Of the ammonites, we have more exact evidence; they were observed by our forefathers, and called by them snake-stones. According to the legends of Catholic saints they were considered as possessing a sacred character:

“Of these and snakes, each one
Was changed into a coil of stone
When holy Hilda prayed.” 

And in addition to this petrifying process, one of decapitation is said to have been effected; hence the reason why these snake-stones have no heads. 

We also find, in the northern districts of our island, that the name of “St. Cuthbert’s beads” is applied to the fossil remains of encrinites. 

Thus we learn that, to a great extent, fiction is dependent upon truth for its creations; and we see that when we come to investigate any wide-spread popular superstition, although much distorted by the medium of error through which it has passed, it is frequently founded upon some fragmentary truth. There are floating in the minds of men certain ideas which are not the result of any associations drawn from things around; we reckon them amongst the mysteries of our being. May they not be the truths of a former world, of which we receive the dim outshadowing in the present, like the faint lights of a distant Pharos, seen through the mists of the wide ocean? 

Man treads upon the wreck of antiquity. In times which are so long past, that the years between them cannot be numbered by the aids of our science, geology teaches us that forms of life existed perfectly fitted for the conditions of the period. These performed their offices in the great work; they passed away, and others succeeded to carry on the process of building a world for man. The past preaches to the present, and from its marvellous discourses we venture to infer something of the yet unveiled future. The forces which have worked still labour: the phenomena which they have produced will be repeated.
 - The Poetry of Science, or, Studies of the Physical Phenomena of Nature,  Robert Hunt, 1854

Likewise, just as dinosaur remains were discovered centuries before Buckley named Megalosaurus and Owens coined the Dinosauria, bones which belonged to what we would now call Plesiosaurs were found and recorded long ago. In 1719, William Stukeley described a "crocodile or porpoise" which was discovered in a quarry in Fulbeck: it is now believed to be a Plesiosaur.

The first remains of Plesiosaurus to be scientifically described were first named by Henry De la Beche and William Conybeare, based upon discoveries made by one of the greatest fossil hunters, Mary Anning.

Orbis Publishing's Dinosaurs! magazine was a treasure trove of comics depicting the history of palaeontology.

Mary's life is practically an adventure novel in itself: she was one of only two children out of ten in her family to survive adulthood - no mean feat considering the shocking child mortality rate of the time, not to mention the time she was struck by lightning as a baby. Anning did not allow wee things like that to hinder her, nor did she let a lack of formal education to get in the way of her enthusiasm for prehistoric life. She taught herself geology, palaeontology, anatomy, and illustration in order to pursue her dreams, and battled the systemic inequality which prevented women from admittance - or even attendance - to the forefront of palaeontological research.

Nonetheless, Anning's friends who were of a gender and class permitted into the scientific circles of the time acknowledged her contributions, and today, she is considered one of the most important figures in palaeontology, with none other than Charles Dickens eulogising her. One thing that seems to unite early palaeontologists is a similar flair for the dramatic:

Of all the inhabitants of the ancient world, this animal is, perhaps, the most anomalous, and the most deserving the name of monster, if we could, indeed, dare to characterize any of the specific productions of Nature by such an appellation.
 -  The Animal Kingdom Arranged in Conformity with its Organization, Baron Cuvier, 1830

That it was marine is evident from its paddles; that it may have occasionally visited the shore, the resemblance of its extremities to those of the turtle may lead us to conjecture; its motion must have been, however, very awkward on land; its neck must have impeded its progress through the water. May it not therefore be concluded—since, in addition to these circumstances, its respiration must have required frequent access to the air—that it swam upon or near the surface, arching back its neck like the swan, and occasionally darting it down at the fish which happened to float within its reach? It may, perhaps, have lurked in shoal water along the coast, concealed among the sea weed, and, raising its nostrils to the surface from a considerable depth, may have found a sure retreat from the assaults of dangerous enemies, while the flexibility of its neck may have compensated for the want of strength in its jaws and its incapacity for swift motion through the water, by the suddenness and agility of the attack which it enabled it to make on every animal fitted for its prey which came within its reach.
 - On the Discovery of an almost perfect Skeleton of the Plesiosaurus, William Conybeare, 1824

It is of the Plesiosaurus that Cuvier asserts the structure to have been the most heteroclite, and its characters altogether the most monstrous that have been yet found amid the ruins of a former world. To the head of a lizard it united the teeth of a crocodile; a neck of enormous length, resembling the body of a serpent; a trunk and tail having the proportions of an ordinary quadruped; the ribs of a chameleon, and the paddles of a whale! Such are the strange combinations of form and structure in the Plesiosaurus - a genus, the remains of which, after interment for thousands of years amidst the wreck of millions of extinct inhabitants of the ancient earth, are at length recalled to light by the researches of the geologist, and submitted to our examination in nearly as perfect a state as the bones of species that are now existing upon the earth.
 - The Bridgewater Treatises on the Power, Wisdom and Goodness of God, as Manifested in the Creation. Treatise VI.: Geology and mineralogy considerd with refernce to natural theology, William Buckland, 1836

This bombastic literary style of scientific discovery was echoed in early palaeoart, where John Martin segued from Biblical Apocalyptic illustration to prehistoric landscapes without skipping a beat:

The earliest three-dimensional reconstructed Plesiosaurs can be found at the Crystal Palace, standing monuments to that early stage of palaeontological discovery, little different from their debut in 1854 save a century and a half's worth of erosion & the occasional refurbishment:

Later palaeoartists like the legendary Charles R. Knight also depicted the Plesiosaurus with an extremely flexible, serpentine neck, which has since been questioned:

The often torrid relationship between science and religion was also punctuated by attempts at reconciliation. The great marine reptiles were viewed by some figures not as contradictions to the Bible, but as reflections of the holy book:

Further it is only in strata formed subsequently to the chalk that we find the remains of those monsters that made the earth to tremble beneath their tread and lashed to foam the billows of the primeval ocean. To those who are unaccustomed to view fossil remains the dimensions of some of these seem almost incredible. Just think of monsters 120 feet in length with teeth eleven inches in diameter and eyes whose sockets were more than eighteen inches across; and we can easily perceive that the statement of Moses is verified, "And God created great whales" (literally sea monsters). Of this epoch, Le Conte says, "It was preeminently an age of reptiles." There are now on the whole face of the earth only six large reptiles over fifteen feet long - two in India, one in Africa, three in America - and none over twenty-five feet long. Yet in the strata that correspond to this period in Great Britain alone are found the skeletons of at least {197} five great Dinosaurs from twenty to sixty feet long, and in the United States the fullness of reptilian life was even greater; for, one hundred and forty-seven species of reptiles have been found, most of them of gigantic size. Among these are fifty species of Mosasaurs, seventy or eighty feet long, also species of crocodiles fifty feet long, besides great numbers of gigantic turtles." These are some of the remains that are still preserved. But the fossil animals of any period are only a remnant of the animals of that period. That the climate of the earth was then warm and uniform is sufficiently attested. All great reptiles are now found only in tropical or subtropical regions; but the remains of these monsters are scattered in all latitudes from New Zealand to Spitzbergen. In all this we see a wonderful agreement between the account given by Moses and the records of geology.
 - Gospel Philosophy, Showing the Absurdities of Infidelity, and the Harmony of the Gospel with Science and History, Elder J.H. Ward, 1884

Of course, nowadays the Plesiosaurus is intertwined with cryptozoology, following early hypothesis from Philip Henry Gosse's The Romance of Natural History (1860) and Henry Lee's Sea Monsters Unmasked (1883) linking modern tales of sea-serpents to Plesiosaurs, to more modern allegations of a certain beastie in a certain Scottish loch first encountered by St. Columba. Even the little Scottish town of Gourock has its own sea monster: science would have you believe it was most likely a basking shark like the Stronsay Monster or Zuiyo-maru creature, rather than a beast from beyond the ken of man, but that's no fun. Regardless of the actuality of the Beast of Cardwell Bay, we know from discoveries at Eigg, Elgin, Raasay, and Skye that plesiosaurs (like Colymbosaurus, "diving lizard," and Plesiosaurus itself) did swim in the waters which once covered Scotland.

Plesiosaurs also, surprisingly, feature in Theosophy: Madame Blavatsky's The Secret Doctrine ponders: "Now we would ask who among the Scientists is ready to prove that there was no man in existence in the early Tertiary period? What is it that prevented his presence? Hardly thirty years ago his existence any farther back than 6, or 7,000 years was indignantly denied. Now he is refused admission into the Eocene age. Next century it may become a question whether man was not contemporary with the "flying Dragons;" the pterodactyl, the plesiosaurus and iguanodon, etc., etc." Similarly, W. Scott-Elliot's The Lost Lemuria (1905) posits that Lemurian Man may have coexisted with such creatures.

This tantalising hypothesis combining stories of terrible beasts lurking in the unexplored realms of the earth with new scientific discoveries of ancient creatures which dwelled in prehistoric seas was a natural inspiration for adventurous writers.

The Plesiosaurus in Literature

Sudden upon the shore 'mid dark, dark slime,
Lengthened a mass most frightful to behold:
Slowly it came, out of the foaming waves.
A breath inflated wide its livid flanks,
And its huge viscid back, with seaweeds sown,
Rose, like a mountain drifted, high in air.
It rose! It rose! It covered all the coast;
Under its wrinkled belly rang the shells;
Its monstrous feet, its big toes hard and scaled,
Were spread out heavy on the shingles wet.
To sounds of far-off winds sometimes the shape
Turned its thin muzzle and its head deformed;
Bristled with hair, dilated like dark caves,
Its nostrils seemed to suck the whole world up
And to despise th' immensities of space;
While its eyes round, rimmed with metallic plates,
Senseless and glassy, swam like two dead moons.
Hideous, it stopped upon the salt sand's edge,
While in long folds its tail still dragged the sea.
Then grinding fierce its large unmeasured teeth,
And wrinkling on its back its serried scales, 
With power, it vented out an outcry long,
Which spread afar beneath the firmament.
By mountains, and by woods of outlines sad,
The clamour solemn, like a billow rolled
To depths of horrid solitudes tenantless.
And the vast universe as in terror heard
The cry immense of life spread in the sky.

 - "The Plesiosaurus," Louis Bouilhet

The discovery of Plesiosaurus and its marine Mesozoic cohorts sparked the public's imagination long before the dinosaurs, in part due to the discovery and popularisation of complete skeletons. The first complete & articulated dinosaur skeleton - John Estaugh Hopkins's Hadrosaurus ("large lizard") - was only formally described in 1858, over three decades after Ichthyosaurus ("fish lizard," 1821), Mosasaurus ("Meuse lizard," 1822), and Plesiosaurus (1824). It took a while for dinosaurs to catch up to their maritime compatriots in popular consciousness.

Where nowadays dinosaur was the go-to prehistoric creature a writer would refer to when they wanted to evoke the ancient and monstrous, Plesiosaurus enjoyed a small cult status instead. Edward Bulwer-Lytton's The Caxtons (1849) wrote "you might as soon have found a Plesiosaurus in the fat lands of Romney Marsh" as a bone in a particularly corpulent individual, and the poor Plesiosaurus was used as an unlovely comparison ever since. Following that, the earliest depictions of Plesiosaurus in fiction could be found in educational works like John Mill's The Fossil Spirit - A Boy's Dream of Geology (1854), which also belonged to the curious "Prehistoric POV" genre.

Such a weird, amazing creature would not have to wait long to feature in science-fiction. The great battle between Ichthyosaurus and Plesiosaurus was immortalised in adventure fiction by Jules Verne's A Journey to the Centre of the Earth (1864), and the great long-necked marine creature proved a mainstay of palaeofiction ever since:

At last have mortal eyes gazed upon two reptiles of the great primitive ocean! I see the flaming red eyes of the Ichthyosaurus, each as big, or bigger than a man's head. Nature in its infinite wisdom had gifted this wondrous marine animal with an optical apparatus of extreme power, capable of resisting the pressure of the heavy layers of water which rolled over him in the depths of the ocean where he usually fed. It has by some authors truly been called the whale of the saurian race, for it is as big and quick in its motions as our king of the seas. This one measures not less than a hundred feet in length, and I can form some idea of his girth when I see him lift his prodigious tail out of the waters. His jaw is of awful size and strength, and according to the best-informed naturalists, it does not contain less than a hundred and eighty-two teeth. 

The other was the mighty Plesiosaurus, a serpent with a cylindrical trunk, with a short stumpy tail, with fins like a bank of oars in a Roman galley. 

Its whole body covered by a carapace or shell, and its neck, as flexible as that of a swan, rose more than thirty feet above the waves, a tower of animated flesh!
 - A Journey to the Centre of the Earth, Jules Verne (Griffith and Farran translation), 1871

Inner Earth Plesiosaurs also turned up in James de Mille's A Strange Manuscript in a Copper Cylinder (1888), while J.J. Astor's A Journey in Other Worlds: A Romance of the Future (1894) posits Jovian lifeforms which are "almost the exact reproduction" of Plesiosaurus. A more unsettling science-fiction depiction of Plesiosaurus can be found in Wardon Allen Curtis's The Monster of Lake Lametrie (1889), which merges cryptofiction with Frankenstein-esque body horror. Plesiosaurus was a celebrity: H.G. Wells himself even mentioned Plesiosaurus in the time-travel adventure:

One cannot choose but wonder. Will he ever return? It may be that he swept back into the past, and fell among the blood-drinking, hairy savages of the Age of Unpolished Stone; into the abysses of the Cretaceous Sea; or among the grotesque saurians, the huge reptilian brutes of the Jurassic times. He may even now - if I may use the phrase - be wandering on some Plesiosaurus-haunted Oolitic coral reef, or beside the lonely saline seas of the Triassic Age.
 - The Time Machine (1895), H.G. Wells

By the end of the 19th Century, Plesiosaurus was so well known that it wouldn't even need to be named for folk to recognise it. One of the most important pieces of palaeofiction is The Lost Continent by C.J. Cutcliffe Hyne, one of the first "lost world" stories to explicitly link ancient mythology - in this case, Atlantis - with contemporaneous scientific knowledge about the prehistoric world. One memorable set piece in the book features the hero as part of a voyaging fleet which is besieged by three familiar "great reptiles":

The vessel was travelling forward faster than a man on dry land could walk. But for the power escape she might as well have been standing still when the beasts sighted her. There were three of them, as I have said, and we saw them come up over the curve of the horizon, beating the sea into foam with their flappers, and waving their great necks like masts as they swam.
 - The Lost Continent: The Story of Atlantis, C.J. Cutcliffe Hyne, 1900

Plesiosaurus continued to haunt the waters of 20th Century fiction in Eden Phillpott's The Archdeacon and the Deinosaurus (1901), Albert Bigelow Paine's The Great White Way (1901), Edwin J. Webster's "The Slaying of the Plesiosaurus" (1903), Vladimir Obruchev's Plutonia (1915), and Richard Dehan's "The Great Beast of Kafue" (1917). While not in a feature role, the Plesiosaurus is also mentioned in Robert W. Chambers' "A Matter of Interest" (1897) and E. Nesbit's 5 Children and it (1905), among many others. And, of course, the Plesiosaurus is one of the denizens of that most archetypal of lost worlds, Maple White Land:

Here and there high serpent heads projected out of the water, cutting swiftly through it with a little collar of foam in front, and a long swirling wake behind, rising and falling in graceful, swan-like undulations as they went. It was not until one of these creatures wriggled on to a sand-bank within a few hundred yards of us, and exposed a barrel-shaped body and huge flippers behind the long serpent neck, that Challenger, and Summerlee, who had joined us, broke out into their duet of wonder and admiration. 

"Plesiosaurus! A fresh-water Plesiosaurus!" cried Summerlee. "That I should have lived to see such a sight! We are blessed, my dear Challenger, above all zoologists since the world began!" 
 - Chapter XIV - "Those Were The Real Conquests," The Lost World, Arthur Conan Doyle, 1912

Burroughs himself introduced the Plesiosaurus in another of his series. The inner earth of Pellucidar boasted seas swarming with them - the larger Tandoraz & smaller Ta-ho-az:

 After passing over the first chain of mountains we skirted a salt sea, upon whose bosom swam countless horrid things. Seal-like creatures there were with long necks stretching ten and more feet above their enormous bodies and whose snake heads were split with gaping mouths bristling with countless fangs. There were huge tortoises too, paddling about among these other reptiles, which Perry said were Plesiosaurs of the Lias. I didn't question his veracity—they might have been most anything. 

Dian told me they were tandorazes, or tandors of the sea, and that the other, and more fearsome reptiles, which occasionally rose from the deep to do battle with them, were azdyryths, or sea-dyryths—Perry called them Ichthyosaurs. They resembled a whale with the head of an alligator. 
 - Chapter IV - "Dian the Beautiful," At The Earth's Core, Edgar Rice Burroughs, 1914

The Lias is the name given to the rock strata of the Early Jurassic which bore the fossils of marine reptiles from the Age of Dinosaurs. The Blue Lias is the subgroup which Mary Anning explored, and the source of those same fossils from which our knowledge of these creatures ultimately began.

Plesiosaurus olsoni 

The incomparable Joe Jusko's take on Plesiosaurus olsoni

... "Look!" cried Olson. "Would you look at the giraffe comin' up out o' the bottom of the say?" We looked in the direction he pointed and saw a long, glossy neck surmounted by a small head rising above the surface of the river. Presently the back of the creature was exposed, brown and glossy as the water dripped from it. It turned its eyes upon us, opened its lizard-like mouth, emitted a shrill hiss and came for us. The thing must have been sixteen or eighteen feet in length and closely resembled pictures I had seen of restored plesiosaurs of the lower Jurassic. It charged us as savagely as a mad bull, and one would have thought it intended to destroy and devour the mighty U-boat, as I verily believe it did intend.
 - Chapter 4, "The Land That Time Forgot," Edgar Rice Burroughs, 1918

Most contemporaneous depictions of Plesiosaurs have a graceful, swan-like neck. Palaeontologists in the early 20th Century argued that Plesiosaurs could coil their necks in a manner similar to Pleurodiran turtles, as depicted above by Charles Knight. Current palaeontological research considers this unlikely, as Plesiosaur necks are not thought to be as flexible as previously argued. This does not necessarily preclude any possibility of rearing necks into a vertical position like cetacean spyhopping (or some of the wilder theories like electrogenic organs and the T-Handled Socket Wrench of Death) - just that it wouldn't have been from a horizontal position.

It’s well known these days that plesiosaurs were almost certainly not capable of the erect-necked or swan-necked poses shown in older artwork: the anatomy is against it, it doesn’t work when we consider their buoyancy and pose in the water, and it’s not consistent with what we understand of their ecology and behaviour anyway. While they should therefore be reconstructed with more horizontal neck poses, it doesn’t follow, however, that they were wholly incapable of maintaining a vertical neck posture for a brief period...

Q: Would Cryptoclidus have engaged in spyhopping behaviour? 
A: I wonder how interested plesiosaurs would have been in seeing things in air. But, then, you can say the same thing about cetaceans (note also that the apparently flattened eyeballs of plesiosaurs mean that their eyesight in air was perhaps not great). As is now reasonably well known, raising the whole neck upwards from the horizontal may not have been possible at all, but, yes, vertical spyhopping remains plausible. Maybe plesiosaurs occasionally wanted to check for flocks of foraging pterosaurs, the vicinity of land and so on.
 - Plesiosaur Peril - the lifestyles and behaviours of ancient marine reptiles

In the early days of paleontology, Plesiosaurus was used as a "wastebasket taxon" - an arrangement into which a number of discoveries were grouped due to lack of any more suitable placement. Therefore, a number of different genera were classed as species of Plesiosaurus in Burrough's time, ranging from smaller creatures like Archaeonectrus ("ancient swimmer"), Microcleidus ("small clavicle"), & Thalassiodracon ("sea dragon"), to mid-sized animals like Attenborosaurus ("Attenborough lizard") & Rhomaleosaurus ("robust lizard"), to huge beasts like Pliosaurus ("more lizard"). At only 16-18 feet (4.9-5.4m) in length, Plesiosaurus olsoni - sadly, the only Caspakian denizen to be granted an unofficial specific name - is quite a bit larger than the type specimen Plesiosaurus dolichodeirus' size (11.5ft/3.5m) though not as large again as the 34ft/10.3m Elasmosaurus platyrurus ("flat-tailed plate lizard"), which remains the largest known long-necked Plesiosaur. Nonetheless, P. olsoni is clearly well within the established fossil record's size range for Plesiosaurids at the time Burroughs was writing.

The "glossy" texture of P. olsoni's back suggests a smooth skin, perhaps like extant sea turtles. This is also supported by contemporary evidence. Remains of "Plesiosaurus" conybeari (now considered a distinct genus, Attenborosaurus conybeari) included skin impressions - unfortunately, those fossils were among a number of precious discoveries that were destroyed during the Second World War blitz.

The brown colouring of P. olsoni is a nice touch on Burrough's part, as it clearly indicates the river-dwelling nature of the creature. Many species of river reptiles are brown in hue, from the brown caiman and dark-spotted anaconda, to multiple species of turtle like the Batagur, Fitzroy, Murray, Pig-Nosed, and Softshell  - Chelonians being the Plesiosaur's closest living relatives. P. olsoni is observed to be positively infesting the great river of Caspak, Tyler suggesting that they'd seen "thousands" of the things - such proliferation in such a comparatively small area as Caprona is one of the many mysteries of the place.

We were moving slowly up the river as the creature bore down upon us with distended jaws. The long neck was far outstretched, and the four flippers with which it swam were working with powerful strokes, carrying it forward at a rapid pace. When it reached the craft's side, the jaws closed upon one of the stanchions of the deck rail and tore it from its socket as though it had been a toothpick stuck in putty. At this exhibition of titanic strength I think we all simultaneously stepped backward, and Bradley drew his revolver and fired.
 - Chapter 4, "The Land That Time Forgot," Edgar Rice Burroughs, 1918

Reptiles have a reputation for being weak, slow and sluggish - largely due to the squamata's energy conservation habits - but the reality is very different. Crocodiles are immensely powerful creatures with enormous stamina compared to mammals:

Estuarine crocodiles appear to be extremely powerful animals. They increase their exercise endurance and tolerances to high lactate and acidosis as they get larger [41], particularly after they reach adulthood, when they engage in territorial and courtship fighting [49]. The crocodiles weighing 100–200 kg violently resisted capture for up to 48 min in our earlier study, and larger animals can struggle for 1–2 hours (GJW Webb, pers. comm.). They produce the highest level of blood lactate known for any animal as a result of activity to fatigue [41]. Although the anaerobic capacity (the total anaerobic energy produced) of crocodiles is high, the anaerobic scope (the rate of anaerobic energy production) is not particularly high. According to this analysis, a 1 kg crocodile has about the same anaerobic scope as a 1 kg mammal, but the scope decreases with increasing body size (Figure 5). Thus, total energy production in a 1 kg crocodile is 57% of that of a mammal, decreasing to 14% at 200 kg (Figure 5). These estimates align with the earlier conclusion that total aerobic and anaerobic performance in reptiles and rodents were similar, because those animals were small, weighing less than 262 g [21]. If the trend continues in crocodiles larger than 200 kg, then the disparity may increase further.
 - Maximal Aerobic and Anaerobic Power Generation in Large Crocodiles versus Mammals: Implications for Dinosaur Gigantothermy, Roger S. Seymour

Still, that's crocodiles: as already stated, Plesiosaurs' closest living relatives are turtles. Surely if there's a creature that epitomises slow, lethargic, and unaggressive, it's the humble turtle, right?

Obviously there are significant morphological differences between the Plesiosaurs and the Testudinata, even before we get to the Caspak Evolutionary Phenomenon. Nonetheless, Burroughs was writing well before the period where popular consensus of prehistoric life shifted towards the "stupid and doomed" model, and the creatures of Caspak were as deadly as they were awesome.

The bullet struck the thing in the neck, just above its body; but instead of disabling it, merely increased its rage. Its hissing rose to a shrill scream as it raised half its body out of water onto the sloping sides of the hull of the U-33 and endeavored to scramble upon the deck to devour us. A dozen shots rang out as we who were armed drew our pistols and fired at the thing; but though struck several times, it showed no signs of succumbing and only floundered farther aboard the submarine. 
 - Chapter 4, "The Land That Time Forgot," Edgar Rice Burroughs, 1918

Similarly, reptiles are known to survive grievous injuries that would be fatal to mammals or birds, so a large Plesiosaur surviving "several" gunshots from turn-of-the-century era pistols is not outside the realms of possibility.

I saw the thing raise one flipper over the rail, dart its head forward and with the quickness of lightning seize upon one of the boches. I ran forward, discharging my pistol into the creature's body in an effort to force it to relinquish its prey; but I might as profitably have shot at the sun. 

Shrieking and screaming, the German was dragged from the deck, and the moment the reptile was clear of the boat, it dived beneath the surface of the water with its terrified prey.
 - Chapter 4, "The Land That Time Forgot," Edgar Rice Burroughs, 1918

Plesiosaurus is currently believed to be a piscivore - understandable given the size of its head and neck - and occasionally may have dined on belemnites and ammonites. Of course, we cannot know for sure if it would dine on humans, but if it did, it wouldn't be a pleasant demise. A sufficiently large Mosasaur could swallow you whole; an Ichthyosaur would shred you in seconds. A Plesiosaur would have to take its time with you, tearing off and swallowing chunks of flesh. And with those teeth, good luck getting out of its grasp!

Of course, that wouldn't be the last siege of the U-33 at the flippers of a Plesiosaur:

At sight of me a huge thing charged and climbed to the deck. I retreated to the top of the conning-tower, and when it had raised its mighty bulk to the level of the little deck on which I stood, I let it have a bullet right between the eyes.  

The thing stopped then and looked at me a moment as much as to say: "Why this thing has a stinger! I must be careful." And then it reached out its long neck and opened its mighty jaws and grabbed for me; but I wasn't there. I had tumbled backward into the tower, and I mighty near killed myself doing it. When I glanced up, that little head on the end of its long neck was coming straight down on top of me, and once more I tumbled into greater safety, sprawling upon the floor of the centrale.  

Olson was looking up, and seeing what was poking about in the tower, ran for an ax; nor did he hesitate a moment when he returned with one, but sprang up the ladder and commenced chopping away at that hideous face. The thing didn't have sufficient brainpan to entertain more than a single idea at once. Though chopped and hacked, and with a bullethole between its eyes, it still persisted madly in its attempt to get inside the tower and devour Olson, though its body was many times the diameter of the hatch; nor did it cease its efforts until after Olson had succeeded in decapitating it. Then the two men went on deck through the main hatch, and while one kept watch, the other cut a hind quarter off Plesiosaurus Olsoni, as Bradley dubbed the thing. Meantime Olson cut off the long neck, saying that it would make fine soup. By the time we had cleared away the blood and refuse in the tower, the cook had juicy steaks and a steaming broth upon the electric stove, and the aroma arising from P. Olsoni filled us all with a hitherto unfelt admiration for him and all his kind.
 - Chapter 4, "The Land That Time Forgot," Edgar Rice Burroughs, 1918

Here, the extreme reptilian aspect of P. olsoni (I have chosen to decapitalise the specific name to bring it further in line with The International Commission on Zoological Nomenclature) is depicted, as Olson goes Barbarian on the creature to little avail. Like a zombie, only removal of the head stops its massive onslaught - and given other reptiles reaction to decapitation (WARNING EXTREMELY GRAPHIC AND HORRIFIC CONTENT) even that might not have been enough to stop it biting for hours!

We had a pleasant meal, with only one unfortunate occurrence—when Olson suggested that possibly the creature we were eating was the same one that ate the German. It was some time before we could persuade the girl to continue her meal, but at last Bradley prevailed upon her, pointing out that we had come upstream nearly forty miles since the boche had been seized, and that during that time we had seen literally thousands of these denizens of the river, indicating that the chances were very remote that this was the same Plesiosaur.
 - Chapter 5, "The Land That Time Forgot," Edgar Rice Burroughs, 1918

The idea a river could have "literally thousands" of Plesiosaurs along a 40-mile stretch is an early hint to Caspak's mystery. As for what P. olsoni would taste like? Well, given their closest living relatives, it could taste like anything from shrimp, fish, chicken, goat, pork, beef, or veal - or, given Caspakian biology, it could taste like nothing else on earth.

Depictions & Successors

Plesiosaurus continued to be a popular icon after "The Land That Time Forgot's" publication. Authors as diverse as Clark Ashton Smith, H.P. Lovecraft, and Ray Bradbury all mentioned or featured the creature:

Nearing the nightward side of Venus which is never exposed to daylight, in a latitude where the sun slanted far behind them as over arctic realms, they beheld through thinning vapors an immense tract of land, the sole continent amid the planetary sea. This continent was covered by rich jungles, containing a flora and fauna similar to those of pre-glacial eras on the earth. Calamites and cycads and fern-plants of unbelievable luxuriance revealed themselves to the earth-men; and they saw everywhere the great, brainless reptiles, the megalosaurs, plesiosaurs, labyrinthodons and pterodactyls of Jurassic times.
 - "Seedlings of Mars," Clark Ashton Smith, 1931

Of the animals I saw, I could write volumes. All were wild; for the Great Race's mechanised culture had long since done away with domestic beasts, while food was wholly vegetable or synthetic. Clumsy reptiles of great bulk floundered in steaming morasses, fluttered in the heavy air, or spouted in the seas and lakes; and among these I fancied I could vaguely recognise lesser, archaic prototypes of many forms - dinosaurs, pterodactyls, ichthyosaurs, labyrinthodonts, plesiosaurs, and the like - made familiar through palaeontology.
 - "The Shadow Out of Time," H.P. Lovecraft, 1936

And then, from the surface of the cold sea came a head, a large head, dark-coloured, with immense eyes, and then a neck. And then - not a body - but more neck and more! The head rose a full forty feet above the water on a slender and beautiful neck.  Only then did the body, like a little island of black coral and shells and crayfish, drip up from the subterranean.  There was a flicker of tail.  In all, from head to tip of tail, I estimated the monster at ninety or a hundred feet.
 - "The Fog Horn," Ray Bradbury, 1951

Bradbury's "The Fog Horn" was the inspiration for The Beast from 20,000 Fathoms, which was itself an influence on Godzilla.

The first cinematic depiction of the Plesiosaurus was in 1926's now-lost The Savage, less than a decade after "The Land That Time Forgot" was published: all that remains of this film is a collection of stills and lobby posters, including this one. Plesiosaurs of some form or another went on to appear in King Kong, Son of Kong, The Land Unknown, and When Dinosaurs Ruled The Earth.

It wasn't until 1975 that P. olsoni was depicted on film, in Amicus Productions' cult classic The Land That Time Forgot.

There are two distinct "Plesiosaurs" which attack the crew in Kevin Connor's film adaptation. The first has a very crocodilian mouth (which prompts Olson to call it a "crocodile" rather than the novel's giraffe, which is only marginally less bizarre a comparison) and a dorsal fin running down the neck, which is more akin to popular depictions of Mosasaurus than Plesiosaurus: this is the creature which makes off with the hapless German crewman, Plesser.

The second creature is noticeably different, and much closer to the popular depiction of Plesiosaurus & the book - it's brown, at least, which is something not all adaptations manage to remember, as we'll see soon. This is the creature which made steak for the crew of U-33, although in the adaptation Olson's axework was substituted for the speedier and far less messy Bergmann MP18. Since the two creatures are quite evidently different species, let alone individuals, the remark about eating the same creature which ate the man in the book doesn't make much sense, so it's omitted entirely.

If you watch carefully, you can see several of the poor Plesiosaur's teeth flying out of their sockets as the head crashes to the deck of the ship - loosened by the barrage of bullets, no doubt.

Rather than utilise the stop-motion techniques of O'Brien & Harryhausen fame, Amicus decided on much more time- and cost-effective puppetry to bring the dinosaurs to life. Most of the puppets were designed by Roger Dickin, who had previous form in palaeopictures by building the Chasmosaurus and Plesiosaurus which Jim Danforth animated magnificently in When Dinosaurs Ruled The Earth. However, the larger "in-frame" puppets - such as the Plesiosaurus - were built by the hugely prolific John Richardson, whose work spans from James Bond to Starship Troopers. It's a bit unfortunate that the two models seem to be two different creatures again:

The smaller Dickin puppet, which menaced Doug McClure via projection...

... and the larger Richardson puppet, which Doug McClure had to fend off physically.

The Dickin puppet is more convincing due to the dexterity which the effects team could work the armature, compared to the unwieldy Richardson one which was limited to the technology of the time. Nonetheless, the Richardson puppet is more accurate to what we know of the creature, particularly in the distinctive, interlocking, procumbent teeth - a hallmark of Plesiosaur physiognomy.

At least one more P. olsoni is seen in the film, as part of the very sad "extinction" at the film's climax:

I've heard there was a 2009 adaptation of "The Land That Time Forgot" produced by some film company somewhere, but I'm certain it's a myth. Nonetheless, for completeness' sake, if such a film existed, then I'm pretty sure they won't even have bothered with P. olsoni any more than they would've bothered retaining any of the characters or plot of the story.

But then, I'm only guessing, because it does not exist.

However, there are a few comic adaptations of "The Land That Time Forgot" which do exist.

Marvel produced one based on Michael Moorcock (yes, that Michael Moorcock) & James Cawthorn's screenplay for the 1975 film, with the talents of the legendary Sonny Trinidad & Marv Wolfman. Trinidad's P. olsoni is not dissimilar to the film adaptation's effects, in particular the smaller puppet.

Scott Alexander Young & K.L. Jones' 2010 adaptation from Campfire Graphic Novels is fairly faithful, and depicts P. olsoni largely in line with the original story - though unfortunately this adaptation depicts P. olsoni as green, rather than the glossy brown of the book. Still, the bloody showdown with Olson is surprisingly accurate for a book aimed at younger readers.

Martin Powell, Pablo Marcos, & Oscar H. Gonzalez's adaptation can be found on edgarriceburroughs.com, which indicates an official seal of approval from the estate - though, again, for some reason the P. olsoni isn't brown, this time a sort of sea-green.

More recently, Mike Wolfer & Giancarlo Caracuzzo's 2016 adaptation from American Mythology Productions is actually more of a sequel (I do wish more people would indicate something's a sequel by not using the same title of the thing it's meant to be a sequel to), which includes Bowen's granddaughter making her way to Caspak in modern times. The cover features P. olsoni in all its toothy glory, although as with the 2010 & 2013 comics, they still give it a different colour, with this adaptation going for a marine blue. (Seriously, it isn't as if Burroughs provides a ton of detail: its colour is one of the only things he actually states!). The sequel was successful enough that a spinoff featuring original character See-Ta the Savage followed soon after.

Plesiosaurus olsoni is one of the most memorable of the Caspakian living fossils despite its comparatively brief appearance: the idea of an aggressive hunting Plesiosaur snatching unlucky humans from aboard a ship presented a threat unlike any other sea creature save perhaps a belligerent cephalopod. It's little wonder that future palaeofiction went straight to the Plesiosaur when it needed a marine reptile to menace the protagonist. Even if the Plesiosaur's neck flexibility and androphagous tendencies had been exaggerated, it remains one of the most iconic denizens of the ancient Mesozoic ocean.