June 25, 2012
Hadrosaurs have often been called “duck-billed dinosaurs.” You don’t have to look at their skulls for very long to see this analogy is wide of the mark. Not only did hadrosaurs such as Edmontosaurus have shovel-shaped, grooved beaks, but their jaws were lined with rows of cropping, crushing teeth. These dinosaurs didn’t dabble in Cretaceous swamps – they grazed the prehistoric plains. And, up until recently, it was thought that these huge herbivores possessed an evolutionary innovation that made them the dinosaurian equivalent to cows.
In general, dinosaur jaws and teeth were for cutting, plucking, and tearing. Dinosaurs didn’t chew their food, but instead ripped or clipped their morsels, which were then swallowed whole. (Strange as it may seem, this style of eating might have had a role to play in why sauropods were able to maintain such large body sizes.) But hardosaurs were thought to be different.
The idea I encountered as a kid was that when hadrosaurs such as Edmontosaurus opened their jaws, the tooth-bearing bones of their upper jaws – the maxillae – swung inwards. Then, when the lower jaws came back up, the lower teeth met the upper teeth and ground the plant food across the tooth surfaces. This wasn’t chewing like mammalian herbivores do it, but it was an evolutionary alternative that allowed hadrosaurs to better break down their food before swallowing. You can see a visualization of this hypothesis in action in this YouTube video.
But this model of hadrosaur chewing required a great deal of flexibility in the skull to create a complex chewing motion. As a video uploaded by the Canadian Museum of Nature – posted above – shows, hadrosaur jaw movements were probably a great deal simpler. The key to the puzzle is the interlocking group of small bones at the back of the skull. When the virtual Edmontosaurus drops its lower jaw, the movement compresses some of these bones at the back of the skull, which moves the upper tooth rows slightly inward. But the lower jaw doesn’t just drop – a joint at the back of the mandible also allows the lower jaw to extend forward. When the jaws close, the lower jaw moves back in a diagonal motion, and the contact of the upper and lower teeth gently push the maxilla slightly outwards. There is still a lot of movement in the skull, but it’s not quite as dramatic as the swingin’ maxilla version. And this goes to show just how much we still have to learn about dinosaurs. Even though we know more about Edmontosaurus and its kin than ever before, the basics of dinosaur biology remain rich grounds for investigation and debate.
[Hat-tip to Thomas Holtz for sharing this video on Twitter.]
June 1, 2012
I was probably too young for my Dinosaurs Attack! cards. When the Topps set popped up at local convenience stores in 1988, I was only five—a touch on the innocent side as I opened the packs of gratuitous dinosaurian carnage. But maybe my naïveté worked to my advantage. Images of Parasaurlophus munching on babies (!) and Stegosaurus thagomizers dashing people’s eyes from their sockets were so over the top that I wasn’t bothered by them. Dinosaurs were supposed to be fearsome and dangerous, right? The gonzo violence looked more or less like what I imagined during my mock battles with little green army figures and plastic dinosaurs.
If you haven’t seen the cards yourself—that is, assuming you want to see them—the entire set is up at Bob’s Dinosaurs Attack! HomePage. The Monster Brains blog also posted the whole run, along with some of the gory promotional images. Don’t expect scientific accuracy. The tyrannosaur on the ghastly “Entombed!” card was pretty good for its time, but the super-size Gorgosaurus with human hands on “Coasting to Calamity” looks like a rejected B movie creature. Speaking of which, a few celebrity monsters make cameos in the set: Godzilla, Gorgo, the Beast From 20,000 Fathoms and the redundantly named Giant Behemoth all show up. Although my favorite “What the heck?” cards are those featuring herbivorous dinosaurs gone bad, such as the carnivorous ankylosaur in “Heartland Horror” and sauropodomorphs that chew the hair of heavy metal musicians in “Rock Concert Carnage.” These cards were sensationally unscientific, but they reminded me that even plant eaters could be dangerous.
As silly, stupid and just pain gross as the series was, it looked like Dinosaurs Attack! was poised to become a major bit of dinosaur culture. A comic series promised to continue the mayhem, a toned-down animated show was pitched, and rumor had it that a major motion picture was in the works. But that all fizzled. The comic only ran one issue, the cartoon never got off the ground and the impending release of Jurassic Park killed hopes for a film. (Instead we got the awful, unfunny Mars Attacks!, a Tim Burton adaptation of the earlier Topps series that served as a template for the unrelated dinosaurian follow-up.)
Done right, though, I think a Dinosaurs Attack! movie could be bloody fun. There have been a few R-rated dinosaur films—the lackluster Carnosaur series being the most prominent—but all the great examples of dinosaur cinema have been toned down for kids. Maybe it’s time for a dinosaur movie that says “This is not fit for children” and really runs with the idea of what life would be like if packs of Deinonychus roamed the streets and an ornery Styracosaurus decided to graze on the front lawn.
April 25, 2012
When I think of Deinocheirus, I think of arms. A few other parts of the dinosaur’s skeleton are known—vertebrae, ribs and most of the hip—but none of those elements are quite as impressive as the immense forelimbs. The arms, tipped with curved claws, measure about eight feet long, and the creature that carried them must have been about as large as the stubby-armed tyrannosaurs that roamed the same habitats in Mongolia around 70 million years ago. The clues from the arms and associated bones hint that Deinocheirus was a gigantic ornithomimid—one of the “ostrich mimic” dinosaurs like Struthiomimus. The trouble is that only the single specimen has been described so far, and so many parts of the skeleton are missing that we don’t wholly know what the gargantuan dinosaur looked like. A new paper, online at Cretaceous Research, suggests that the dining habits of tyrannosaurs might explain why paleontologists didn’t find more of Deinocheirus.
Deinocheirus was discovered in 1965 by the Polish-Mongolian Palaeontological Expedition. To find out more about this dinosaur, in 2008 members of the Korea-Mongolia International Dinosaur Project tracked down the quarry that yielded the single known specimen. The paleontologists hoped that the original excavations had left some bones behind, or that new pieces of the dinosaur’s skeleton might have been exposed in the intervening time.
According to the Cretaceous Research paper by Phil Bell, Philip Currie and Yuong-Nam Lee, the search turned up multiple bone fragments and several gastralia—the “belly ribs” that formed a basket beneath the dinosaur’s ribcage. And those gastralia may explain why so little of Deinocheirus became preserved. Two of the slender, curved bones recorded the bite marks of a large predatory dinosaur. This Deinocheirus was being eaten shortly before burial.
There are many kinds of bite marks. Paleontologists can categorize them, and each pattern of damage corresponds to different biting behavior. The Deinocheirus gastralia exhibited two different kinds of bite marks: tooth scores and parallel striations created as the serrations of the carnivorous dinosaur’s teeth scraped along the bone surface. The minute troughs suggest that a large tyrannosaur, most likely Tarbosaurus, fed on the Deinocheirus. Since the striations record the number and shape of bumps called denticles on the feeding dinosaur’s teeth, they act like a sort of dental fingerprint. Of all the theropod dinosaurs found in the same geologic formation, only Tarbosaurus seems to have had teeth that match the damaged bones.
We can’t know whether the tyrannosaur killed the Deinocheirus or scavenged it. While healed bite wounds record attacks that the victim survived, unhealed bite marks only show that the dinosaur was consumed before burial. In this case, it seems that the tyrannosaur opened up the stomach of the Deinocheirus for access to the viscera inside, but the bite marks record only those brief, violent moments. Whether the tyrannosaur brought down the Deinocheirus or just happened across a rotting carcass is a mystery. But the tyrannosaur also ensured that the particular Deinocheirus would remain an enigma. As the Tarbosaurus feasted, it dismembered the body and scattered the bones of its prey. If paleontologists want a complete look at Deinocheirus, they are going to have to hope for another skeleton elsewhere.
Bell, P.R., Currie, P.J., Lee, Y. (2012). Tyrannosaur feeding traces on Deinocheirus (Theropoda:?Ornithomimosauria) remains from the Nemegt Formation (Late Cretaceous), Mongolia Cretaceous Research : 10.1016/j.cretres.2012.03.018
March 5, 2012
Though only about the size of a turkey, Velociraptor still looked like a formidable predator. With snatching hands, a jaw set with recurved teeth and, of course, a retractable claw on each foot, almost every end of this dinosaur was sharp. But what did this well-equipped Cretaceous killer actually eat?
One of the prime candidates for a Velociraptor entree has been the small horned dinosaur Protoceratops. A truly spectacular fossil cemented the connection between these dinosaurs. In 1971, a Polish-Mongolian expedition to the Gobi Desert found “fighting dinosaurs“—a Velociraptor and Protoceratops preserved in the throes of fatal combat. While the Velociraptor had kicked its deadly foot claw into the neck of the Protoceratops, the little ceratopsian had crushed the right arm of the predator, and the two remained locked together in death. The trouble is that we can’t know why these two dinosaurs were fighting. Was the Velociraptor trying to hunt the Protoceratops? Or was the little predator itself attacked by a territorial Protoceratops? That the dinosaurs battled each other is obvious, but the reason for their combat remains a mystery.
But a recently described fossil confirmed that Velociraptor or a very similar dinosaur ate Protoceratops flesh. In 2010, paleontologist Dave Hone and co-authors reported a set of Protoceratops bones that had been scratched and scored by the teeth of a small predatory dinosaur. How the horned dinosaur died was unclear, but the toothmarks indicated that the carcass had almost been entirely stripped by the time the carnivorous dinosaur came along to pick off the remaining scraps. Since Velociraptor shared the same habitat and was of the right size to leave the bite marks, the dinosaur is a good candidate for being the scavenger.
Another fossil provides an even closer connection between Velociraptor and its prey. In a paper to be published in Palaeogeography, Palaeoclimatology, Palaeoecology, Hone and co-authors Takanobu Tsuihiji, MahitoWatabe and Khishigjaw Tsogtbaatr describe part of a Velociraptor meal preserved inside the dinosaur’s body cavity. Represented by a single bone, the gut contents show the dinosaur had fed upon a pterosaur.
The broken pterosaur bone was probably inside the dinosaur’s stomach when it died. How that bone found its way into the Velociraptor digestive system is another matter. Based on the anatomy of the bone and the pterosaurs that were around at the time, Hone and colleagues hypothesize that the ingested pterosaur was an azhdarchid, one of the long-legged, long-necked pterosaurs that included the largest flying animals of all time.
This particular pterosaur was not a giant by pterosaur standards—Hone and colleagues estimate that the animal probably had a wingspan over six feet across and weighed more than 19 pounds. But it would have been large compared to the relatively small Velociraptor that consumed it. This would have made the sharp-beaked pterosaur “a difficult, and probably even dangerous, target [for] a young dromaeosaur,” Hone and co-authors suggest, and therefore “unless the pterosaur was already ill, infirm or injured, it seems unlikely that this would be a case of predation.” And the fact that the dinosaur consumed a large bone further suggests this might have been another instance of Velociraptor scavenging. If the pterosaur carcass was fresh, the Velociraptor probably would have consumed the available soft tissues first. The fact that the dinosaur ate bone may be an indication that the pterosaur had been picked over and there was only a little meat left clinging to the carcass.
This isn’t the first time evidence of small dromaeosaurs scavenging on pterosaurs has been found. In 1995, paleontologists Philip Currie and Aase Roland Jacobsen reported a partial skeleton of an azhdarchid pterosaur that had been bitten by a small predatory dinosaur. A tooth embedded in the skeleton identified the scavenger as Saurornitholestes, a dromaeosaurid cousin of Velociraptor from Cretaceous North America.
Although Velociraptor is often celebrated as a vicious and cunning predator, the accumulating evidence shows that the dinosaur wasn’t above scavenging. This isn’t surprising. Even highly active predators will regularly scavenge if the opportunity arises. And while I consider the ballyhooed argument over whether Tyrannosaurus rex was primarily a hunter or scavenger to be dead and buried—the tyrant dinosaur was certainly both hunter and scavenger—it is worth noting that even small, apparently highly predaceous dinosaurs at least occasionally scavenged. In outlining his case for “Tyrannosaurus the scavenger,” paleontologist Jack Horner pointed to Velociraptor as the epitome of what a predatory dinosaur should look like. Yet this new paper, as well as other recently reported indications of dinosaur hunting and scavenging, underscores the fact that the hunting-scavenging dichotomy is too narrow a view on nature. As Hone and colleagues wrote near the beginning of their paper, many carnivores hunt and scavenge. The trick is figuring out which type of flesh-acquisition behavior was more important to a particular species.
Frustratingly, though, we’re more likely to find evidence of dinosaur scavenging than active predation. Relatively small predators like Velociraptor, which may have specialized on even smaller prey, are especially troublesome in this regard. Unless someone is lucky enough to find a small mammal, dinosaur, or other creature in the gut contents of Velociraptor, we may never know what this dinosaur primarily hunted. When predatory dinosaurs wrenched tattered bits of flesh from denuded carcasses, though, they often left tell-tale signs of damage behind, and these traces are more likely to be preserved than are gut contents. Despite its celebrity, we are still just beginning to put together a picture of how Velociraptor hunted and fed.
Currie, P., & Jacobsen, A. (1995). An azhdarchid pterosaur eaten by a velociraptorine theropod Canadian Journal of Earth Sciences, 32 (7), 922-925 DOI: 10.1139/e95-077
Fowler, D., Freedman, E., Scannella, J., & Kambic, R. (2011). The Predatory Ecology of Deinonychus and the Origin of Flapping in Birds PLoS ONE, 6 (12) DOI: 10.1371/journal.pone.0028964
Hone, D., Choiniere, J., Sullivan, C., Xu, X., Pittman, M., & Tan, Q. (2010). New evidence for a trophic relationship between the dinosaurs Velociraptor and Protoceratops Palaeogeography, Palaeoclimatology, Palaeoecology, 291 (3-4), 488-492 DOI: 10.1016/j.palaeo.2010.03.028
Hone, D., Tsuihiji, T., Watabe, M., Tsogtbaatr, K. (2012). Pterosaurs as a food source for small dromaeosaurs Palaeogeography, Palaeoclimatology, Palaeoecology : 10.1016/j.palaeo.2012.02.021
July 25, 2011
Big, predatory dinosaurs were well-adapted to stripping flesh from bone. That’s obvious from the shape and size of their teeth. What has been more difficult to determine, however, is how they behaved as they ate. Studying bones scored with the toothmarks of carnivorous dinosaurs is one of the most direct ways to approach questions about how predatory dinosaurs fed. One such bone—a tail vertebra of the sauropod Pukyongosaurus found on the Korean peninsula—shows that at least two different predators each had their shot at the same carcass.
The damaged bone is described in an in-press Palaeogeography, Palaeoclimatology, Palaeoecology paper by In Sung Paik and colleagues. The paleontologists report that at least five parts of the bone show toothmarks, including gouges, V-shaped scores and divot-shaped lesions. Since the bones of the sauropod dinosaur were otherwise in good condition—they did not exhibit cracks that would indicate that the bones had been lying on the surface for a long time—Paik and co-authors propose that the dinosaur was rapidly buried near the site of death, meaning that all these toothmarks were made in a narrow window between death and burial. Whether or not the sauropod was killed by a predator cannot be determined. All that is clear is that the toothmarks were left after the Pukyongosaurus died.
So what sort of carnivorous dinosaurs left the tooth marks? That is difficult to say. Most of what is known about big predatory dinosaurs on the Korean peninsula comes from teeth attributed to dinosaurs akin to Allosaurus and tyrannosaurs. Big theropods were certainly around in the right area at the right time, but they are almost entirely a mystery.
Nevertheless, the patterns of the toothmarks indicate a few things about how the predatory dinosaurs ate. Some of the marks, for example, are arranged in parallel rows which indicate that the feeding dinosaur was nipping or scraping with teeth at the very front of the jaw, perhaps at a time when the rest of the easily-accessible flesh had been stripped off. Additionally, while three sets of marks appear to have been made by a large animal, there are two that appear to have been left by a smaller carnivorous dinosaur at a time when most of the flesh had been removed. Were the two dinosaurs of different species? Could they have been an adult and a juvenile of the same species? How much time passed between when the big dinosaur fed and the little one tore off the remaining scraps? No one knows, but the traces left on the sauropod bone provide paleontologists with a murky window into an ancient encounter between predator and prey.
Paik, I.; Kim, H.; Lim, J.; Huh, M.; Lee, H. (2011). Diverse tooth marks on an adult sauropod bone from the Early Cretaceous, Korea: implications in feeding behaviour of theropod dinosaurs. Palaeogeography, Palaeoclimatology, Palaeoecology : 10.1016/j.palaeo.2011.07.002