Friday, April 29, 2011

Kronosaurus: The King (or Queen) of the Queensland Sea

Life was good during the Early Cretaceous – about 110 million years ago – in what would some day become Queensland, Australia. That is, life was good for whatever was making tucker out of whatever else was alive at that time. In that sense, then, when it came to the Cretaceous seaway that covered much of inland Australia then, few animals enjoyed life more than the giant marine reptile Kronosaurus queenlandicus.
Fancy a dive in the Cretaceous sea of Queensland? You’d have a lot more to worry about than running into a box jellyfish, blue-winged octopus, or great white shark, mate, like a bloody huge Kronosaurus. Artwork is on a tapestry (batik?) in Kronosaurus Korner, Richmond, Queensland, and the presumed artist is Paul Stumkat, who’s also the curator and fossil preparator there. (When you do paleontology in central Queensland, you have to wear a lot of hats.)

Last July 2010, while on a paleontological drive-about (not to be confused with a walkabout) in central Queensland with my wife Ruth, we ended up in the small town of Richmond. Our stopping in Richmond was not random, as I had visited there in 2007 and was thoroughly impressed with the alliteratively (and illiteratively) named fossil museum there, Kronosaurus Korner. So we were visiting to see this facility and its paleontological displays, including the remains of the enormous Cretaceous predator that inspired the museum’s name.
And just who, er, I mean, what was Kronosaurus? It is classified as a pliosaur, and pliosaurs were an evolutionarily related group of marine reptiles that lived during the latter part of the Mesozoic Era, from about 200 to 90 million years ago. Although pliosaurs chronologically overlapped with dinosaurs, they were separated by habitats, as dinosaurs were mere land-dwellers and pliosaurs probably never willingly left the ocean. Pliosaurs shared a common ancestor with another group of marine reptiles – plesiosaurs – but differed from those by having large skulls relative to their total body lengths and short necks. Both groups, though, had flippered limbs that were well adapted for swimming.

Why have a large skull? Normally this trait has nothing to do with holding a bigger brain, but rather for supporting the ability to bite through anything that might be in your environment. Kronosaurus was a great example of a big-time biter, having dozens of 25-cm (10-in) long pointy teeth and a skull about ¼ of its body length. How long was that? Its adult body lengths are estimated to have been about 8-10 m (26-33 ft), although that has been the subject of controversy, as explained later.

Here’s a small piece of a Kronosaurus skull (above) compared to the full-sized skull of a much-feared modern aquatic reptile of Australia, the estuarine crocodile (Crocodylus porosus), also known as “salties” for their occasional sea-faring ways. I don’t know about you, but I would rather take my chances with a “salty” instead of a “Krony.” Display at Kronosaurus Korner, Richmond, Queensland.
As can be surmised from its species name, Kronosaurus queenlandicus hails from Queensland. The type specimen was found in 1899 near the town of Hughenden, consisting of just a lower jawbone (mandible) with a few teeth. Paleontologist Heber Longman named it in 1901, although at first he thought it was an ichthyosaur. Like many scientists, though, he later corrected this mistake. (We scientists are funny about that: it’s almost as if science has self-correction built in as part of its process.) In the 1920s, station owner Ralph Thomas found the most famous specimen of Kronosaurus on his ranch (Army Downs) north of Richmond. He told a fossil-hunting team from Harvard University about it, and they decided to collect the specimen so it could be studied.
Only thing was, this specimen was really big (we’re talking “Tyrannosaurus big”), and its bones were still encased in sandstone, which meant that taking it out and transporting it would not be easy. So it was broken into 86 pieces, with some of fragmentation accomplished by dynamite, strategically placed by a field assistant nicknamed “The Maniac” (no, I am not making that up). In 1932, all 4-5 tonnes of rock containing the bones were shipped back to the U.S., and the bones have stayed there ever since.

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 for Australians who don’t feel like traveling to the eastern U.S. to see their pliosaur, more specimens have been found since, and these have stayed in Australia, including several at Kronosaurus Korner (appropriate, that).
A partial skeleton of Kronosaurus showing the lower outline of its skull, preceding part of a front limb and a few of its vertebrae, namely the neck (cervical) and back (dorsal). Specimen on display at Kronosaurus Korner, Richmond, Queensland.
Moving the specimen to the U.S. did not mean it would be seen by the public in all of its pointy-toothy glory any time soon, though. Extraction of the skeleton took 27 years, and it was not revealed to the public at the Harvard Museum of Comparative Zoology until 1959. The detailed story of this ordeal, as well as the genius of its preparation and mounting by James Jensen, Sr. (“Dinosaur Jim”) is told by his son, James Jensen, Jr. here.

 A classic photo of the classic specimen of Kronosaurus, originally from Queensland, Australia, but now on display at the Museum of Comparative Zoology (Harvard University), with the mysterious Lady in Red for scale. Little does she know that this specimen is wearing the fossil equivalent of lifts. Wish I could credit the photographer, but I understand it's originally from a postcard, and the digital image comes from always-excellent Oceans of Kansas web site.

Tragically, I have not seen this specimen of Kronsaurus, which happens to be much closer to my home (Atlanta, Georgia USA) than central Queensland. The skeleton, displayed beautifully in the Museum of Comparative Zoology at Harvard (Cambridge, Massachusetts), is only about a two-hour flight from Atlanta, so perhaps I should make a trip to see it sometime. (Mental note: Start going to major natural-history museums in the eastern U.S.)

The odd thing is, the original skeleton was nowhere near as complete as the mounted version might imply. Evidently, too many vertebrae were added to its back, making it about 13 meters (42 feet) long, and enough plaster was added to the mount that it gained the facetious nickname of “Plasterosaurus.” So now paleontologists think that Kronosaurus might have been “only” 8-10 meters (26-33 feet) long. But hey, what are a few meters among friends when you’re a Cretaceous pliosaur?
Another partial skeleton of Kronosaurus giving more of a sense of its total length: partial skull in front extending back to its tail (caudal) vertebrae, with a few paddled limbs thrown in for good measure. My lovely wife Ruth is serving as a scale in the back, fulfilling the cliché about geologists (and paleontologists) that their only photos of people are as scale. Incidentally, she’s 1.8 m (5.8 ft) tall.
Is Kronosaurus found only in Australia? One fossil says “no.” A geologically older species of KronosaurusKronosaurus boyacensiswas discovered in 1992 in Cretaceous rocks of northern Columbia, a place far away from both Queensland and Massachusetts. Nevertheless, when you’re a large marine reptile during a time of very high sea level (which the Cretaceous had), you and your relatives could get around. So they did.
OK, I know what you’re thinking. (No, not that, although you’re close.) You’re wondering, “But wait: aren’t you an ichnologist? What are you doing talking about some big marine reptile and its body fossils?” Well, here’s Example #1,243 why trace fossils kick butt yet again (and I never get tired of reminding everyone of that fact). For a long time, paleontologists didn’t know what Kronosaurus ate, but trace fossils helped to provide some answers.
At first, large shelled cephalopodsammonites and nautiloids – were proposed as the most likely candidates for Kronosaurus fodder. This hypothesis made sense because of: (1) the co-occurrence of many large nautiloid and ammonite fossils in the same Cretaceous deposits holding the remains of Kronosaurus; and (2) its massive size and banana-sized teeth implied that these were used for crunching hard-shelled or hard-boned animals, of which nautiloids and ammonites certainly qualified.
Mmmm…Cretaceous calamari [drooling sounds]. Otherwise known as nautiloids (above) and ammonites (below) to marine biologists, paleontologists, or anyone else who loves cephalopods. Specimens on display at Kronosaurus Korner.
But there are two problems with that hypothesis. Thus far, no nautiloids or ammonites have been found as stomach contents in Kronosaurus, and no shells of either animal have been found with toothmarks matching the dental records of Kronosaurus. The first of those two facts is excusable, considering how few specimens of this enormous pliosaur have been found, let along ones with their gut regions intact. The second fact, though, is tougher to explain as an absence of evidence. Cephalopods in general (including squid) are very abundant as body fossils in the Cretaceous marine deposits of Queensland. So you would think someone would have found one or more examples that had been punctured by a Kronosaurus. So far, not yet.
Did any other Cretaceous reptiles munch on these molluscans? Yes, but not in Australia, and not by Kronosaurus. This behavior has been documented through trace fossils in Cretaceous marine deposits of North America for paleoecologically analogous marine reptiles, the awesome mosasaurs. These toothmarks show up as circular punch-marks on ammonite shells, which also line up in a way that they correspond with the tooth row of a mosasaur.
These holes in an ammonite shell were either made by small gastropods (limpets) or are toothmarks from a mosasaur. I don't have to tell you which hypothesis is sexier, but science tends to go for "brainy." Which, of course, is the sexiest. Regardless, I'm going with the biting hypothesis. So these marks in a Late Cretaceous nautiloid shell from the U.S. are credited to a mosasaur teaching its young to kill. In this scenario, the big ones (AT) are from the adult and the small ones (JT) are from the juvenile. Figure from: Kauffman, E. (2004), Mosasaur predation on Upper Cretaceous nautiloids and ammonites from the United States Pacific Coast, Palaios, v. 19, p. 96-100.
However, one prominent ichnologist – Dolf Seilacher – disagreed with this hypothesis and argued that these traces also may have been scars made by limpets, which are gastropods that like to attach to hard substrates, like shells. This set off a bit of a scientific tussle, as the “pro-biters” took on Seilacher and other “pro-attachers” who agreed with his hypothesis. No one was disputing that these ammonites had a bunch of big holes and some animal caused them, but the explanations for these features were so radically different from one another, it was worth a good argument.
The last I’ve heard, though, is that the “pro-biters” have regained some favor, as they described a few ammonite specimens showing fracture patterns consistent with biting by an animal with massive and powerful jaws. One paleontologist (Erle Kauffman) even interpreted repeated biting as possible evidence of an adult mosasaur teaching its young how to kill ammonites. How cool is that? It’s ichno-cool.
Speaking of ichno-cool, trace fossils provide a clue that Kronosaurus may have been at least biting (if not eating) other large marine reptiles swimming in the same Cretaceous seaway. The skull of an Australian elasmosaur (a type of plesiosaur), Woolungasaurus glendowerensis, has some marks on its skull consistent with crushing by large teeth. Could it have been from Kronosaurus? Maybe, but a few more specimens showing more clear evidence would be nice. Of course, that hasn’t stopped some paleo-artists from depicting Kronosaurus victimizing Woolungasaurus.
Skull of the Early Cretaceous elasmosaur Woolungasaurus glendowerensis that had the misfortune of putting its head inside the head of another animal with really big teeth (like a Kronosaurus); look at the puncture mark (arrow). Specimen on display in the Museum of Tropical Queensland.
Unfortunately, as far as I can find from my (admittedly non-exhaustive) literature reviews, this idea of “Kronosaurus skull-crushing fury” has not been tested rigorously yet, and certainly not as much as the “mosasaur chomping ammonite” hypothesis. One trace fossil that would really help would be a massive coprolite. Size alone would tie it to Kronosaurus, and the contents would tell us directly just what went through its gut (or at least the gut of one such animal). Other coprolites attributed to marine reptiles have been recognized from the same Cretaceous deposits (some of which were on display at Kronosaurus Korner), so I hold out hope that someone, some day, will find an enormous pile of fossil sea-dung.
So if Kronosaurus were around today, what would it eat? It probably would go for large fish – maybe even sharks – and take a bite out of the soft parts of an occasional sea turtle or marine mammals. I can’t help but think that the pack-hunting orcas would turn the tables and make short work of one, though. Nonetheless, I have some photographic evidence suggesting other potential prey, especially if a Kronosaurus came up onto land:
 Bloody hell! Don’t drive right into its mouth, mate! And here you thought veering around ‘roos and staying awake were the worst hazards of driving a lorry in the Queensland outback.
Too much plastic in the world’s oceans? Here’s one solution: bring back Kronosaurus to get rid of your rubbish!
Anyway, all of this goes to show us that, despite our knowing about its presence in the Cretaceous seas of Australia for more than a hundred years, we still have a lot more to learn about this magnificent marine reptile. May Kronosaurus queenlandicus stay alive in our paleontological thoughts, and my best ichno-wishes that trace fossils will somehow tell us more about how it lived.

I just can’t get enough of this beautiful, inspirational song – From Little Things, Big Things Grow, by Kev Carmody – and was delighted to know that two of my favorite Australian singers - Sara Storer and Archie Roach - had covered it. It’s not about Kronosaurus, but about peaceful change, which pretty much cover paleontology and a lot else in life.


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