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A blow-up pliosaur at National Geographic headquarters, courtesy of Amanda Bensen Fiegl

Pliosaurs are not technically dinosaurs, but they were fellow travelers. Both clades lived in the Jurassic and Cretaceous Periods, went extinct about 65 million years ago and were gigantic, toothy and bizarre.

Former Food & Think blogger Amanda Bensen (now Fiegl) left Smithsonian a few months ago to take a job with our arch-nemesis, National Geographic. She snapped this photo of a blow-up 45-foot pliosaur in front of her new office building; it’s there to promote a program called “Death of a Sea Monster.”

Note the lovely cherry blossoms—it’s springtime in Washington.

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You can track previous dinosaur sightings here.

A reconstruction of Stegosaurus on display at the Carnegie Museum of Natural History. From Flickr user Kordite.

Stegosaurus had a formidable tail. Studded with four long spikes, this dinosaur’s business end would have given Allosaurus and other Jurassic predators plenty of incentive to keep moving. But do we have any evidence that Stegosaurus really used its tail this way?

Among paleontologists, the four-spiked tail of Stegosaurus is called a “thagomizer.” It is one of a few terms inspired by one of Gary Larson’s beloved “Far Side” cartoons: a caveman points to a slide of a Stegosaurus tail and names the nasty-looking structure in honor of “the late Thag Simmons.” Humans and Stegosaurus missed each other by over 140 million years, but the joke was so perfect that paleontologists couldn’t help but informally use it.

Whether Stegosaurus—and similarly equipped armored dinosaurs—used their thagomizers as weapons has been a minor point of scientific debate. The spikes certainly look like weapons, but that, by itself, isn’t sufficient to tell what their function was. Paleontologists needed some kind of evidence of direct interaction between predator and prey, and in 2005 paleontologists Kenneth Carpenter, Frank Sanders, Lorrie McWhitnney and Lowell Wood reported just that.

Printed in The Carnivorous Dinosaurs, the paper by Carpenter and colleagues looked at several lines of evidence for interactions between Stegosaurus and one of the apex predators of its day, Allosaurus. First, a plate from the neck of a Stegosaurus found in Utah’s Cleveland-Lloyd Quarry had a prominent, U-shaped notch taken out of its edge. The front portion of the jaws in Allosaurus corresponded closely to the missing piece, and since the plates were bony rather than carrying any significant amount of flesh, the paleontologists proposed that the missing chunk represented an attack rather than feeding or scavenging.

A second line of indirect evidence came from the Stegosaurus spikes themselves. Out of 51 examined spikes, about ten percent had broken tips with remodeled bone. Stegosaurus were clearly losing the sharp ends of their spikes and surviving for long enough afterward for the bone to start to heal, adding support to the idea that they were being used for defense and were not just for show.

But the most impressive piece of evidence was a single Allosaurus tail vertebra found in the Cleveland-Lloyd Quarry and known as UMNH 10781. You need to know a bit about Allosaurus anatomy to see what’s wrong with this bone. Sticking out at an angle from the circular body of the vertebra, there is a wing of bone called the transverse process. In this particular specimen that process is missing a piece of bone measuring about an inch and a half square. This wasn’t a break or evidence of damage after death. As with the tail spikes of Stegosaurus, the outside edges of the hole show evidence of remodeled bone, meaning that this Allosaurus was injured and survived for some time after being hurt.

The bite of another theropod doesn’t fit the pattern of damage. There are no tell-tale toothmarks, nor is there evidence of crushing. Instead, the damage appears to have been caused by a large, pointed object, and a diagram included in the paper shows how a Stegosaurus tail spike fits the hole perfectly. The Stegosaurus may have even left part of itself behind. While bone around the outer edges of the vertebra shows signs of healing, the wound itself doesn’t show the same signs of repair, which led Carpenter and co-authors to suggest that part of the Stegosaurus spike remained lodged in the hole, perhaps just part of the tough outer sheath that would have made the spikes even pointer in life.

Carpenter and colleagues also went a step further in modeling the physics of how Stegosaurus might have used its tail and the damage it could have inflicted. They concluded that the spikes would most likely slash open wounds if the attacking Allosaurus was standing in parallel to the Stegosaurus, but if the predator came in perpendicularly or at another angle the spikes of Stegosaurus were more likely to lodge in the skeleton and break. In these cases both predator and prey would have been injured. Stegosaurus certainly had enough swing to deal out some heavy damage to an attacking Allosaurus, the scientists concluded, but the problem was driving in its spikes with so much force that they might break!

References:

Carpenter, Kenneth; Sanders, Frank; McWhinney, Lorrie A.; and Wood, Lowell (2005). Evidence for predator-prey relationships: Examples for Allosaurus and Stegosaurus The Carnivorous Dinosaurs, 325-350

A Nazi tank on top of a dinosaur? Sure, why not? Image courtesy of Steam Apps.

How is a Saurpod Like a Vacuum Cleaner? Find out at Everything Dinosaur.

Renaissance Reptiles: Art Evolved alerts us to the opening of Dinosauri in Carne e Ossa, the first large-scale paleoart exhibition in Italy. The event will be running through May 31 in Piacenza—a city renowned for its historical palaces and renaissance churches. And now, it also has dinosaurs. (Your move, Venice.)

The War of Art: A blogosphere battle royale has erupted in response to comments posted on the Dinosaur Mailing List by pioneering paleoartist Gregory S. Paul. As Asher Elbein writes over at The Faster Times, Paul “made a sweeping statement to the paleoart world: stop using my skeletal reconstructions. This sparked a massive discussion…Did he have the right to prevent artists from making use of his technical and scientific skeletal illustrations for the purposes of their own reconstructions? How far did his copyright claims extend? And most importantly, can you copyright the exact proportions of an animal skeleton?”

Love in the Time of Chasmosaurs has dubbed the debate, the “paleoart-pocalypse,” and is posting regular updates on his blog.

New Blog on the Block: Let’s extend a warm, paleosphere welcome to Skeletal Drawing, a blog that “will deal with the functional anatomy of dinosaurs and other extinct critters…as well as the limits on what can be confidently restored in extinct animals.” Be sure to check out the blog’s three-part series on “A History of Skeletal Drawings.”

Rex Riders: Looking for t-shirts featuring homo sapiens riding on dinosaurs? Dinochick has you covered.

Nazi Dinosaurs: Finally, someone has recognized the one crucial element that’s been missing from World War II strategy games: dinosaurs. Kotaku offers a preview of “Dino D-Day,” which will be released in early April. The premise, according to the game’s manufacturer: “The year is 1942. Adolf Hitler has succeeded in resurrecting dinosaurs. The reptilian horde has trampled Europe and the Mediterranean. Can nothing stop the Nazi’s dinosaur army?”

The Write Stuff: Greg Leitich Smith, author of novels for young adults—including the forthcoming dino-themed time-travel mystery, The Chronal Engine—is starting a blog series called Writers and Dinosaurs. “The idea is to feature children’s authors and illustrators in photos with dinosaurs of some kind. These can be realistic dinosaurs or skeletons from natural history museums or theme parks or can be dinosaurs of the more cartoon-y variety. So if you’re an author or illustrator and have a picture and want to be included, leave a comment with your email and I’ll be in touch!”

Remember the Woodcraft dinosaurs? I loved playing with those skeletal plywood puzzles as a kid, and a giant-sized version of one recently made a guest appearance on the show The Amazing Race. A few of the competing teams were tasked with putting together plus-sized Dilophosaurus skeletons, though I bet a true dinosaur fan would have kicked their tails.

A reconstruction of Albertosaurus at the Royal Tyrrell Museum in Canada. Image from Wikipedia.

When I was in elementary school, I was told that mammals and reptiles could easily be told apart by their teeth. Mammals had a full, enamel-covered toolkit in their mouths—incisors, canines, premolars, and molars suited to different tasks—while reptiles had only one kind of tooth. The dental differences were presented as one of the ways in which mammals were superior to reptiles, but like a number of other things I was taught in grade school, this wasn’t quite right.

Not all mammals have differentiated sets of teeth. Dolphins, for example, have jaws full of nearly identical, conical teeth. Among reptiles, on the other hand, multiple species have been found with a variety of tooth shapes in their jaws. Pakasuchus, an extinct cousin of modern crocodiles found in the 105-million-year-old rock of Tanzania, had three different types of teeth in its jaws, and even the mighty Tyrannosaurus and Albertosaurus possessed differentiated teeth. What this meant for how the tyrant dinosaurs ate was addressed in a Canadian Journal of Earth Sciences paper by Miriam Reichel last year.

Although the teeth of Albertosaurus and Tyrannosaurus may seem to be all the same, these dinosaurs actually had three different tooth classes. The teeth at the front of the jaw are small and closely packed; those in the middle of the jaw are exceptionally long and curved and those at the back of the jaw are smaller and only slightly recurved. (The differences between the teeth can perhaps best be seen in the skull of the juvenile Tyrannosaurus “Jane“.) What Reichel wanted to know was how these various teeth functioned, and so she created computerized, 3-D models of Albertosaurus and Tyrannosaurus teeth to test how they would have held up to the stresses and strains created by biting.

As might be expected for large predators, the teeth of both tyrant dinosaurs were suited to different tasks. The small and stout front teeth were likely used for pulling large pieces of meat from carcasses, the much larger teeth in the middle of the jaw were adapted to coping with the stresses of struggling prey, and the teeth at the rear of the jaw were positioned to deliver heavy, crushing forces in an arrangement Reichel likened to a clamp.

There was one notable way in which Albertosaurus and Tyrannosaurus differed, though. Albertosaurus had a matching set of upper and lower teeth—their functions were consistent from front-to-back along the jaw—but in Tyrannosaurus the patterns of the upper and lower teeth differed. Specifically, the teeth at the front of the lower jaw in Tyrannosaurus were not adapted to pulling off chunks of flesh, but were instead suited to withstanding forces associated with capturing prey. Perhaps, Reichel suggests, this is because Tyrannosaurus had a slight overbite in which the teeth at the front of the lower jaw were closest to the large, prey-capturing teeth near the middle of the upper jaw, meaning that they changed in function to compensate for the alteration in jaw position.

Lacking live tyrannosaurs to study, paleontologists will surely continue to find ways to model the bites of these famous dinosaurs. It is not an easy task. Teeth, bones, muscles, ligaments, and other aspects of the living animal must all be accounted for and combined to create a picture of the entire dinosaur. We do not have a fully comprehensive understanding of tyrannosaur bites just yet, but the more we discover about their jaws, they more terrifying the tyrants become.

References:

Reichel, M. (2010). The heterodonty of Albertosaurus sarcophagus and Tyrannosaurus rex: biomechanical implications inferred through 3-D models Canadian Journal of Earth Sciences, 47 (9), 1253-1261 DOI: 10.1139/E10-063

SMITH, J. (2005). HETERODONTY IN TYRANNOSAURUS REX: IMPLICATIONS FOR THE TAXONOMIC AND SYSTEMATIC UTILITY OF THEROPOD DENTITIONS Journal of Vertebrate Paleontology, 25 (4), 865-887 DOI: 10.1671/0272-4634(2005)025[0865:HITRIF]2.0.CO;2