This is a strange figure. It's really not a very good representation of Kronosaurus. Marx looks more like a sea lion than a short-necked pliosaur. The head of the real-life Kronosaurus was bigger, with a more bulbous cranium (maybe), the body was more compressed dorsal-ventrally, and the neck was much shorter. To be fair, I think Marx got the tail just about right. And the main virtue of the Marx figure was that we had a Rubber Dino Kronosaurus at all. In later years, some others came along - one from Safari in the Carnegie series, and a Liopleurodon (same basic idea as Kronosaurus) from Invicta. But for a long time, all we had in the pliosaur department was the Marx incarnation (and its MPC knockoff).
There is one mounted specimen of Kronosaurus on display. He is at the Harvard Museum of Natural History in Cambridge, Massachusetts. Here's how he got there. [Sorry, nothing there yet - Under Construction]
Harvard rents the hall out for "functions." I hope that's not seafood they're serving there ....
[UPDATE - the page has moved, even if Harvard hasn't. Hmmm, let's see ... try here. New page, new photo, same ol' Kronosaurus.]
See another great photo of this specimen on Adam Smith's Plesiosaur Directory.
[UPDATE - Holy Mother of Pearl, another dead link. Well, no great challenge, The Plesiosaur Directory is now here.
Here's a reconstruction from Colbert. There doesn't seem to be any sound basis for the inclusion of that dorsal fringe, and the illustrated tail is too long and flexible, but I think the rest shows the right idea -
So where did the Marx reconstruction come from?
Maybe Rudy Zallinger - of Yale Age of Reptiles mural fame - is partly to blame. The fragment below is not from The Age of Reptiles - I believe it was commissioned by Life for their famous World We Live In series, circa 1953.
Well, that pretty much looks like it, a Zallinger pastische - a Kronosaurus head and neck, tacked onto an Elsamosaurus body, flippers, and tail.
The bulbous swellings at the roots of the flippers remain inexplicable. But at least there's rarely any trouble reading the markings on these Marx figures -
Kronosaurus was one of the three figures made in the original Marx "large" mold, # PL749, and was made from about 1955 to about 1961. He mainly appeared in gray or light green, although sometimes was found in Play Sets in metallic green or metallic silver. I don't believe he ever appeared in brown plastic, as that color was introduced to the Marx series around the time the "large" mold was retired. He was long out of production by the time Marx dinos began appearing in tan. He was not reissued in the early 1970s.
Kronosaurus was made in a three-segment mold - left, right, ventral.
Markings - KRONOSAURUS and 50' LONG, both on ventral surface.
There have been a few copies of the Marx Kronosaurus - see MPC and ELM.
Although Kronosaurus is lumped in with the other Rubber Dinos, he was a short-necked pliosaur, and not a dinosaur at all. His classification is slightly unsettled but in the older references tends to appear as Sauropterygia Plesiosauria Pliosauroidea Pliosauridae Kronosaurus. Carroll (Vertebrate Paleontology and Evolution, 1988) gives that classification for superorder / order / superfamily / family / genus. Romer (Vertebrate Paleontology, 3rd ed, 1966) gives the same basic scheme but as order / suborder / superfamily / family / genus. A real oldie, von Zittel (GrundzŁge der Palšontologie Vol. III, revised 1916, further revised 1925), concurs with Romer but doesn't bother with a superfamily.
What that boils down to is that the Plesiosauria includes as subdivisions the Plesiosauroidea and Pliosauroidea. The Plesiosauroidea are the ones with long necks and relatively small heads. The most extreme development along this line was Elasmosaurus (himself an old Rubber Dino favorite - see Invicta and Safari/Carnegie versions, as well as numerous Bucket 'O Dinos ones I haven't pictured). The Pliosauroidia have short necks and huge heads. At first glance the pliosaurs are easily confused with the mosasaurs, but their somatic structures are entirely different, as were their modes of locomotion and maybe their eating mechanisms. The typical pliosaur had a much stiffer body, with a maze of overlapping ribs on the ventral side. The construction currently in vogue imagines the creature propelled by front flippers, sticking out to the sides, flapped up and down like wings, and the rear flippers moving more like frog's legs, with the short tail just along for the ride. Mosasaurs would have been far more flexible and likely to swim much like crocodilians, with a sinuous motion of the body and long tail, and the flippers folded back alongside the body, or perhaps extended a bit for manuevering.
Kronosaurus was native to the Lower Cretaceous of Australia. Colbert (Age of Reptiles) gives 50 feet or more (~15 meters) for his overall length, with the jaws being more than twelve feet (3.6 meters) of that. Romer (Vertebrate Paleontology) sets him at a mere 40 feet plus (~ 12 meters). Size isn't everything, but it's enough - more about this contentious issue here.