STUPENDEMYS, the world's largest TURTLE

 PLESIOTURTLE by Thomas Finley

   Imagine yourself a passenger on a time machine that suddenly deposits you in a foliage covered jungle swamp on the edge of a lake. A quick glance around and you are taken aback by the sheer number and variety of crocodilian residents floating about the reeds edge, eyes above water, lurking silently. Suddenly, an explosion of foam and water by the shoreline and a 40 foot monster called Purussaurus leaps onto land and takes down a 1000 pound herbivore. Elsewhere out on the lake, huge domed objects, the size of a mini-van, break the water's surface and cruise along, looking much like the famous Nessy hump shaped back you've heard about so many times. Up on shore, 15 foot tall creatures, standing bipedally are stripping the leaves off the trees.

If this sounds like a typical Jurassic day, you may be surprised to know that the scene described took place just 8 million years ago in Urumaco, South America, some 55 million years after the demise of the Dinosaurs.  

   Every so often, Paleontologists will hit the jackpot and make totally unexpected, monumental discoveries. Such was the case in the summer of 1972, when a Harvard paleontological expedition working in post Tertiary deposits of northern Venezuela dug up the remains of several huge fossil turtles. One of these turtles was bigger than any still living Chelonian and eventually proved to be the largest turtle ever recovered, even bigger than the previous champion giant, the Cenozoic oceanic Archelon.



ARCHELON

Turtles probably constitute the most readily recognizable group of all vertebrates, with their trademark shell consisting of two parts, a dorsal carapace and a ventral plastron. Both sides are connected through a boney bridge, which completes the encasing of organs and even the shoulder girdle, a unique feature among living vertebrates. It's a feature one must go back to the Triassic Placodonts, almost a quarter billion (235,000,000) years ago to see it in any other animals.

PLACOCHELYS

As early as the 1930's, American oil companies like Texas Petroleum were scouting out Venezuela looking for new oil fields to tap, and in the process unearthed some interesting Miocene through Pliocene fossils. By the 1950's, Paleontologists from South America took up the fossil search in their own backyard. In 1972, Bryan Patterson from the Museum of Comparative Zoology at Harvard led an American expedition to Urumaco, and their discoveries led to the first series of publications on specific aspects of the Urumaco fauna, including many new turtles and crocodilians, one of which would turn out to be the world's largest turtle.

   Of the several new turtle species, team expert Roger Wood determined that the biggest one recovered existed fairly recently, swimming in the Venezuelan lakes, rivers and swamps perhaps up to just a few million years ago. This giant, aptly named Stupendemys Geographicus was a Miocene/Pliocene, fresh water aquatic turtle of gigantic size. The shell alone was estimated to be nearly eleven feet long !

 The team uncovered an almost complete carapace, along with partial fragments. The shell was unearthed in an upside down position and detailed examination of the scute arrangement (shell pattern) led Wood to the conclusion that this was of the super-family Pelomedusidae, a type of Pleurodira. Pleurodiras are the sub-order of the order of turtles we know best here in North America, the Cryptodiras. Pleurodiras are also known as "side-necked turtles," because they retract their necks into their shells by folding it over onto itself, unlike the direct retraction method used by the Cryptodiras. Pleurodiras at one time were the dominant order, having worldwide distribution, but today are only found south of the equator.  They are the sub-order responsible for the snake neck turtles (Chelidae), which include what is commonly referred to as one of the world's weirdest animals, the Mata Mata Turtle. 

Different neck retraction of the 2 orders.

   This uniqueness of Pleurodiras can be attributed to the long term isolation of Australia and surrounding islands from the rest of the world, as well as South America and Africa, to a lesser degree. Thus the most recent evolutions of the Pleurodiras took a different route than their northern counterpart Cryptodira since being isolated by continental drift, some 30 to 60 million years ago. 

Pleuridirad Snake Neck Turtle with Mata Mata to the right
among Cryptodiras

   Despite physical similarities with it's extant relative, Podocnemis, the size of Supendemys was beyond immense, perhaps more than 100 times larger than the largest currently known South American Pleurodira. Along with the shell, some fragments of the plastron were recovered along with a massive, hulk-buster humerus bone that Wood speculated was most likely hinged into a huge modified leg/paddle, a feature found on the modern day Carretochelys, a small Indonesian fresh water turtle quickly approaching extinction at the hand of man.



Pig Nose Turtle (Carretochelys) lives in fresh water, has fins and swims fast !

   Wood described the shell of Stupendemys as "gigantic with a depressed carapace pocked with irregular nodular contours on external surfaces and a deep median notch at the front. The anterior border of the nuchal bone is thickened and upturned in a curved collar configuration that is unique among Chelonians. The carapace is low arched and flattish, in the manner typical of aquatic turtles."

Stupendemys Geographicus showing recessed nuchal at top of shell

   Stupendemys had features that resembled modern Pelomedusids but also had different features as well. Enough in fact for Wood to describe it as "aberrant." Other unusual anatomic differences from modern peliomedusids include the placement of the glenoid (arm) socket, which faces forward rather than laterally like the modern podocnemis exspansa. This hints at the strong possibility that the animal did have fins or paddles, swimming via a modified breast-stroke. 

Possible powerful huge finned Stupendemys

   Despite Wood making the supposition that the massive humerus could be realized in the form of a huge paddle or arm/fin combination, subsequent museum representations of Stupendemys do not usually follow his original vision of the animal and complete models sometimes portray a lumbering giant Terrapin with curiously atrophied limbs.

AMNH's  rather weak representation of Stupendemys

   And in further contrast to some of the cumbersome recreations, the original estimates of a heavily laden animal were later dispelled when Marcelo R. Sanchez-Villagra showed that the composition of the shell was not a solid bony type but a criss-crossed matix of fibrous tissues resulting in a lighter weight carapace, such as fiberboard in construction, retaining strength but losing much weight in the process. That weight saving could serve to add extra speed to it's swimming abilities as would the large paddle- fin.
   Huge fins on a large turtle give it carte blanche for international travel, something borne out by the sub-artic hopping leatherback turtles (dermochelys). The only other vertebrate that has a wider natural distribution are some species of whales.

   Given what Wood has written about the humerus, one should think that these creatures were powerful swimmers, confirming what we already know about big humerus bones in turtles. The oversized humerus of the Galapagos Tortoise for example, bears the weight of the animal (up to 300 pounds) and extra weight is not a problem. 

Zoologist Gazillionaire Walter Rothschild

   In the leatherback turtle the big humerus is manifested in a large front paddle of maximum surface area resulting in great speed when needed. Leatherback turtles can swim as fast as the world's fastest Olympic sprinters. Wood 's final summation was that "Stupendemys was a highly aquatic type of turtle, most probably a fresh water preferring example but possibly being able to live in salt water too. One or more pair of limbs were most likely modified into flippers and the head and neck may have retracted in a different manner than current side neck turtles." 

   Stupendemys existed at a time when proto-humans walked the earth, making them much more acceptable as a potentially surviving species, taking into account the order of Testudians' ability to have survived the Tertiary event that wiped out the dinosaurs, it should make them a top modern day candidate for large unidentified aquatic reptiles as described from Loch Ness, Lake Champlain and other large lakes. Add to that, turtle's present proven survivability, adaptability, diversity, potential extreme size and extreme range of distribution in the world.

Snake Necked Pleurodira

   There are gaps in the fossil record in the progression of Pleurodira, especially the snake necked turtles. If Stupendemys represents it's family with extreme gigantism, then what could represent and maybe still represents the possibly equally giant predecessors to the current day snake-necked turtles ?


Paleontologist Dr. Kenneth Carpenter proposes an adapted live birthing
 Plesioturtle as The Loch Ness Animal

   If there was a snake necked turtle with flippers that was also 100 times bigger than today's versions, then you may have a creature that looks much like a Plesiosaurus would be expected to look like. Considering the difficulty in obtaining even one fossil example of the Stupendemys, it is conceivable that there may be a recent Snake Necked Turtle equivalent waiting to be unearthed or even a currently living example waiting to be positively identified.

PLESIOTURTLE proposed for a KING KONG remake.
c/o  Mike Playfair

   On many occasions, lake monster and sea serpent witnesses have mentioned that the creature had "turtle-like" features. And in other instances the sighting has been accompanied by a foul odor, another trademark of the snake neck turtle, which is nick-named "stinkpot" in it's native Australia. Both of these features were observed with the infamous Pensacola "sea-serpent" attack, among others. 

The lone survivor of the Pensacola attack described a "turtle-like"
monster and drew this picture

   As confirmed by our current zoological knowledge about the living 300 species of Chelonians, anything that looks turtle-like should be a turtle. Also given the creature's abilities to withstand cold water, hibernate for months at a time, be omnivorous, swim deep and fast, have worldwide distribution, amazing breath holding ability, an internal gill system that produces oxygen while submerged, have camouflage abilities and the newly discovered ability to produce underwater high frequency complex communications - unclassified gigantic turtles should be considered a top candidate for the identity of many lake monsters and unknown sea creatures claimed around the world.

Publicly unseen still from forensic investigator's files seems to show huge unknown
turtle in Lake Champlain.

                                                    

Face compared to aquatic turtle



Illustration showing position of animal in upper photo

                                                  
                                         
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