The Frustrating Legacy of “Plasterosaurus”

For one of the most impressive seagoing predators of all time, Kronosaurus queenslandicus did not receive a very auspicious introduction in the scientific literature. Today the creature’s name immediately conjures up the image of a massive marine reptile with a cavernous maw arrayed with big, conical teeth, but in 1924, when Kronosaurus received its formal name, the nature of this beast was only briefly outlined in a note by Queensland Museum director Heber Longman in a note given the thrilling title “Some Queensland Fossil Vertebrates.”

Though Longman lamented that the fossil fragment used to name Kronosaurus offered only a “tantalizingly incomplete” look at the marine reptile, he was sure that it was “[a] fragment of a very massive sauropterygian mandible” which “demonstrate[d] the existence in Australia in Cretaceous times of a reptile far larger than any yet put on local record.” The scrap had been known been Heber for some time. The piece had been forwarded to the museum in 1899 by a “Mr. A. Crombie” from Hughenden, Queensland and been mistaken by paleontologist C.W. De Vis as part of the shark-shaped marine reptile Ichthyosaurus. Longman realized that this was a mistake when he carried out his own research on an ichthyosaur skull in 1922, and two years later he concluded that the unique jaw fragment signaled the existence of an imposing variety of marine predators called pliosaurs in the seas of prehistoric Australia.

Pliosaurs were a particular group of big-headed and often short-necked plesiosaurs. This might sound a little confusing since – in museum displays and encyclopedias of prehistoric life – the term “plesiosaur” is most often used for round-bodied, long-necked animals such as Elasmosaurus and, of course, Plesiosaurus. But both the big-headed and the long-necked forms belonged to the group we call plesiosaurs. Together these two forms they represent two sides of a deep split within the plesiosaurs, with the pliosaurs on one side and the long-necked plesiosauroids on the other. (Such is the trouble with talking about prehistoric life – as family trees are bestowed with new branches and evolutionary patterns become more complex, the big scientific picture is often failed by a restricted popular nomenclature.)

In Longman’s estimation, the partial Kronosaurus jaw fragment most closely resembled its counterparts in big pliosaurs like Pliosaurus and Peloneustes found in the Mesozoic strata of England. Frustratingly, though, these animals were also known from bits and pieces. Future fossil discoveries were necessary to determine what they looked like, though Longman was certain that his decision to separate Kronosaurus out as a distinct genus would be “fully justified” by more complete fossil remains.

Longman would have his confirmation a few years later. In 1932 he reported that a few additional fragmentary parts of Kronosaurus – including parts of the paddle-shaped limbs – had been found near Hughenden, and on the basis of this material he hazarded a reconstruction of the whole animal using Charles William Andrews’ 1913 vision of Peloneustes as a guide. (Since I do not have Longman’s 1932 paper nor Andrews’ 1913 monograph, though, I can’t say how close this hypothetical Kronosaurus was to those that were to follow.) It was also about this time that William Schevill, a graduate student from Harvard University, found even more Kronosaurus parts, including the components of the most famous and controversial specimen of this marine reptile.

Schevill was part of an expansive collecting trip launched by Harvard’s Museum of Comparative Zoology. Part of the goal was the bring back specimens of Australia’s marsupial mammals, but Schevill also found part of the snout of a relatively small Kronosaurus in Queensland’s Grampian Valley. While in the vicinity, a sheep rancher named R.W.H. Thomas tipped Schevill off to some strange bones sticking out of his land, and the fossils turned out to be an articulated, nearly-complete Kronosaurus entombed in a grave of hard limestone nodules. Exhuming the skeleton wasn’t easy. In The Rarest of the Rare, a photographic tour of the Museum of Comparative Zoology, author Nancy Pick wrote:

Because the bones were embedded in sold limestone, Schevill enlisted help from a British migrant trained in the use of explosives. The follow – nicknamed The Maniac, due to rumors that he had killed a man – dynamited out huge blocks of limestone encasing the fossils. The blocks were then shipped to Harvard, each on weighting some six tons.

This was the best Kronosaurus specimen yet found, and Australian paleontologists were none too happy with a bunch of New Englanders swooping in to cart off one of the most impressive parts of Australian prehistory. Paleontologist Tony Martin, who recently wrote about Kronosaurus on his blog The Great Cretaceous Walk, commented “Yes, this sort of Yankee paleo-imperialism still rankles with people I talked with in Queensland, with which I agree, considering how taking a fossil too away from its place of origin can reduce our understanding of it.” Fortunately, additional Kronosaurus specimens have been found, but the fact that the archetypal specimen was shipped off to Harvard remains a sore spot.

It took a number of years for the Kronosaurus Schevill’s team collected to become famous, though. The skeleton was so massive, and the number of limestone blocks so numerous, that another quarter century was needed to get this sea monster our on display. Museum of Comparative Zoology scientists Alfred Sherwood Romer and Arnold Lewis outlined the history of the specimen in a 1959 report in the institution’s journal Breviora.

The skull was the first part to be prepared and described. Paleontologist T.E. White undertook the task about two years after the material arrived and published an obscure note on it in 1935, but the bones sat in storage for another two decades after that. Only after a local businessman with a long-running interest in sea monsters – industrialist Godfrey Cabot – offered to pony up about $10,000 to finish the prep work on Kronosaurus did paleontologists begin the difficult task of cleaning the bones, filling in the missing parts of the skeleton, and mounting the amalgamation of fossil bone and plaster. (The duties for reconstructing the animal went to David Fuller and Jim Jensen, the latter expert being the LDS paleontologist who was highly influential in developing the paleontology program at Utah’s Brigham Young University.)

Like many other reconstructed and mounted skeletons, the Kronosaurus at the Harvard museum was a hypothesis. “[E]rosion had destroyed a fair fraction of this once complete and articulated skeleton,” Romer and Lewis wrote, “so that approximately a third of the specimen as exhibited is plaster restoration.” Among the missing parts – the front flippers and parts of the backbone, and the uncertainty about the number of vertebrae made it difficult to accurately estimated how long the animal was. The paleontologists settled on a generous 42 feet, with the creature’s gargantuan head making up about one fourth of its length. Restored as if it were about to chomp down on an unfortunate victim, the Harvard Kronosaurus was truly a monster worthy of its namesake in the mythological gallery of Greek titans.

But, despite the animal’s fame, Kronosaurus is still poorly understood. The significant amount of false bones used in the Harvard mount has gained it the nickname “Plasterosaurus”, and much of what has been written about Kronosaurus exists in obscure museum papers published during the first half of the 20th century. As it stands now, there is some uncertainty about whether the fossil scrap Longman originally used truly represents the same species as the specimen rigged up and restored at Harvard. At least two quirks of the historical record complicate efforts to resolve this problem – the exact locality and age of the specimen Longman used to establish the name is unknown, and the specimen at Harvard is partially locked in plaster. These specimens, as well as others attributed to Kronosaurus from Australia, probably belong to just one genus, but whether they belong to more than one species is unknown. In a review of Australian marine reptiles published in 2003, paleontologist Benjamin Kear wrote “[A]ny attempt at resolving species-level relationships must await a thorough re-examination of the Harvard material and assessment of the undescribed remains currently housed in the Queensland Museum, Brisbane.”

Even without a detailed redescription of the Harvard material, though, paleontologists know that the reconstruction probably differs from what Kronosaurus was truly like in life. For one, thing, it’s too long. Under Romer’s direction, Jensen and Fuller may have added as many as eight vertebrae too many, and, according to remarks by paleontologist Colin McHenry reported in The Rarest of the Rare, the Harvard Kronosaurus should probably measure a more modest thirty feet. The head of the Harvard mount may also be too deep. The original skull reconstruction, assembled by White, was relatively flat and streamlined, but Jensen and Fuller found a strange hunk of bone embedded within the plaster of this earlier reconstruction which they thought belonged on the outside. This piece was placed on top to provide a large ridge for the massive jaw muscles of Kronosaurus to attach to, but, based upon on specimens found since 1959, it appears that White’s more streamlined rendition was closer to the real thing.

Overall, Kronosaurus may have looked significantly different from its most popular manifestation. (Richard Ellis, in his book Sea Dragons, quotes McHenry as explaining that “Rather than looking like a killer whale with big flippers, Kronosaurus was more of a sea lion with the skull of a croc.”) Since the Harvard specimen is a combination of bone and plaster hung up on the museum wall, though, figuring out how its bones should truly be arranged is a frustratingly difficult task. Efforts to preserve and reconstruct Kronosaurus have actually hindered the ability of paleontologists to study the creature. Scientists are still hoping to become better acquainted with one of the most formidable predators of the Cretaceous seas.

[My thanks to Anthony Martin and Paul Stumkat (curator of the Kronosaurus Korner Fossil MuseumKronosaurus Korner Fossil Museum in Queensland, Australia) for helping me obtain the papers by Longman and Romer/Lewis that made up the background for this post.]

Top Image: The Harvard Kronosaurus (sometimes called “Plasterosaurus”). Image from Flickr user arcticpenguin.

References:

Kear, B. (2003). Cretaceous marine reptiles of Australia: a review of taxonomy and distribution Cretaceous Research, 24 (3), 277-303 DOI: 10.1016/S0195-6671(03)00046-6

Ellis, R. 2003. Sea Dragons. University Press of Kansas: Lawrence. p. 177

Longman, H. A. 1924. Some Queensland fossil vertebrates. Memoirs of the Queensland Museum 8:16-28.

Pick, N., and Sloan, M. 2004. The Rarest of the Rare. HarperResource: New York. p. 68

Romer, A. S. and A. D. Lewis. 1959. A mounted skeleton of the giant plesiosaur Kronosaurus. Breviora 112:1-15.