April 17, 2012
Sauropods were swamp monsters. At least, that’s what books, movies, and illustrations taught me when I first encountered the huge dinosaurs. If Diplodocus and Brachiosaurus didn’t actually spend most of their time in the water, then the dinosaurs always stayed close to watery refuges where they could escape from Allosaurus and other predators.
But starting in the 1960s, a renewed scientific interest in dinosaurs overturned this cherished imagery. Sauropods were wholly terrestrial creatures. These giants did not possess any features related to an aquatic or amphibious lifestyle—Apatosaurus and kin were often plunked down into bogs and lakes in reconstructions because that environment seemingly answered nagging questions about the biology of these animals. But early 20th century paleontologists didn’t think that all sauropods were equally adept at life in the water. Rather than take the line that all sauropods were skilled swimmers, paleontologists identified at least one Jurassic sauropod that probably spent more time on land.
In 1920, a trio of American Museum of Natural History scientists published a pair of short papers on the sauropod Camarasaurus. This dinosaur, with a blunt head and spoon-shaped teeth, was one of the better-known members of the classic Morrison Formation fauna, and the AMNH paleontologists had just completed a major reexamination of the dinosaur’s remains. In the first note, Henry Fairfield Osborn and Charles Mook briefly summarized the results of their study, and in a second, accompanying missive, William Gregory outlined the dinosaur’s life habits.
Camarasaurus didn’t seem suited to a life wallowing in a Jurassic lake. While Gregory mentioned that the dinosaur “might well have been an efficient wader,” the dinosaur was also “positively devoid of special adaptations for swimming.” The dinosaurs limbs, shoulders and hips were clearly suited to supporting the animal’s bulk, and Gregory considered the “relatively small and feeble” tail of Camarasaurus to be of no help in swimming. While Gregory did waffle on the habitat the dinosaur preferred, the overall picture was of a relatively straight-limbed dinosaur that carried its body high off the ground. Sauropods did not drag their bellies through the Jurassic mud, as other paleontologists had suggested under the supposition that sauropods were like lizards or crocodiles, writ large.
The following year, when Osborn and Mook published their massive revision of sauropods collected by Edward Drinker Cope, they similarly cast Camarasaurus as a dinosaur that was “terrestrial in gait but adapted to an amphibious life.” And the plates of that paper present some of the restorations and reconstructions previously mentioned in the PNAS papers. A model of Camarasaurus, created by artist Erwin Christman under Gregory’s direction, showed the dinosaur walking on land with slightly bent forelimbs, similar to how the museum mounted its great “Brontosaurus” skeleton years before. Christman and Gregory also collaborated on a pair of skeletal reconstructions—one with the head of Camarasaurus held high, and the other in a droopy pose, with neck and tail slung low.
Osborn, Mook and Gregory’s insistence that Camarasaurus was an amphibious dinosaur, or at least frequently waded, is puzzling. The paleontologists didn’t justify this part of their argument. Sauropods were simply considered synonymous with warm, luxuriant swamps. Contrary to this belief, the experts explicitly pointed out evidence that Camarasaurus walked tall and had a skeleton well-suited to holding up the animal’s weight while walking on land. Even before the “Dinosaur Renaissance” forever changed dinosaurian imagery, early 20th century paleontologists were already cataloging the same evidence. They just saw that evidence differently, in the context of a lazy Mesozoic world filled with shuffling, basking sauropods.
Gregory, W.K. 1920. Restoration of Camarasaurus and life model. PNAS. 6, 16-17
Osborn, H.F., Mook, C.C. 1920. Reconstruction of the skeleton of the sauropod dinosaur Camarasaurus Cope (Morosaurus Marsh). PNAS. 6, 15
Osborn, H.F., Mook, C.C. 1921. Camarasaurus, Amphicoelias, and other sauropods of Cope. Memoirs of the American Museum of Natural History, new series, 3, 247-387 (plates LX-LXXXV).
Taylor, Michael P. 2010. Sauropod dinosaur research: a historical review. pp. 361-386 in: Richard T. J. Moody, Eric Buffetaut, Darren Naish and David M. Martill (eds.), Dinosaurs and Other Extinct Saurians: a Historical Perspective. Geological Society of London, Special Publication 343.
February 29, 2012
For decades, paleontologists have been debating how Triceratops stood. Did old “three-horned face” hold its forelimbs straight up and down like other dinosaurs, or did the horned dinosaur waddle along with its elbows out to the side? The dinosaur’s skeleton has not delivered an unambiguous answer. The critical articulation of the upper arm and shoulder can be reconstructed in a range of positions, and so it’s little wonder that different researchers have arrived at disparate conclusions.
According to paleontologist John Hutchinson of The Royal Veterinary College in London, reconstructing how dinosaurs like Triceratops walked from bones alone is very tricky. “Bones themselves tell you only a bit about locomotion or posture,” Hutchinson said. “Soft tissues and the nervous system have a huge role in such behaviors, so paleontology has long struggled to get past those unknown soft tissues to tackle the cool questions about behavior.” The few known ceratopsid footprints haven’t helped that much—the identities of the trackmakers are often ambiguous, and it can be difficult to relate the pattern in the tracks with the anatomy of an unknown species. “To me,” Hutchinson said, “biomechanics is the best way to integrate all those data and test questions about behavior.”
In a paper published last week in the Proceedings of the Royal Society B, Hutchinson and Shin-ichi Fujiwara of the University of Tokyo proposed a new biomechanical technique to test some of the previously proposed ideas about Triceratops posture. Instead of using skeletal articulation alone as a guide, Hutchinson said, “basically we estimated the moment arms (leverages) of key elbow muscles in three dimensions, using landmarks on the bones.” This method, he explained, allowed the researchers to “determine how the elbow is mechanically supported against gravity.” Fujiwara and Hutchinson then measured a variety of modern animals and determined that the moment arms reflected particular postures. This relationship, they conclude, could be used to study prehistoric creatures. “That gave us extra confidence that we could apply the method to extinct animals, so off we went to study some nicely preserved fossils that could illuminate controversial forelimb postures,” Hutchinson said.
Fujiwara and Hutchinson incorporated several different sorts of extinct creature in their study, including Triceratops. They found that the dinosaur probably had upright forelimbs that were held close to the body—a conclusion also supported by evidence from the dinosaur’s anatomy, scaling patterns and rare footprints attributed to horned dinosaurs. Nevertheless, Hutchinson explained that other evidence might indicate a semi-erect, sprawling forelimb posture. “I don’t think the controversy is over by any means,” he said, “but our method tips the scales closer to the upright end of the spectrum.”
Triceratops wasn’t the only dinosaur in the study. Fujiwara and Hutchinson also studied Protoceratops—a much smaller ceratopsian from Cretaceous Mongolia—to see how the forelimbs of horned dinosaurs might have changed with size. The results were ambiguous, Hutchinson says, but Protoceratops may have “had fairly upright forelimbs, albeit maybe no so much as Triceratops did.” This small ceratopsian, therefore, “would be a reasonable approximation of what the distant, smaller ancestor of Triceratops may have stood or moved like,” although Hutchinson stressed the need to obtain additional details from a wider range of horned dinosaurs.
Hutchinson also noted that the technique utilized in the study is “a new tool in the arsenal of techniques for reconstructing limb postures in land tetrapods.” The method can be extended to a variety of extinct animals with controversial limb postures. In addition to the dinosaurs, Hutchinson explained:
[W]e applied our method to desmostylians (giant hippo/pig-like aquatic mammals), whose forelimb poses have been the subject of a controversy similar to that for ceratopsids. We found quite similar results for 2 genera of desmostylians as for Triceratops—they too seem to have been more upright on land. Similarly, the pterodactyloid Anhanguera emerged as having upright forelimbs, although our analysis cannot address the controversy over whether it was a biped or quadruped, so these results need to be taken with a grain of salt. As a reality check, we also applied the method to a recently extinct thylacine, which video and photos tell us was upright, and obtained that result, which was reassuring.
Perhaps, by combing this technique with other lines of evidence, paleontologists will eventually solve the mystery of the Triceratops slouch.
Fujiwara, S., & Hutchinson, J. (2012). Elbow joint adductor moment arm as an indicator of forelimb posture in extinct quadrupedal tetrapods Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2012.0190
November 1, 2010
Did ceratopsid dinosaurs like Triceratops and Styracosaurus walk with their forelimbs held straight beneath their bodies or splayed out to the side? According to 3-D models created by artist Alex Tirabasso for the Canadian Museum of Nature, the truth lies somewhere in between.
Paleontologists have been debating the forelimb posture of ceratopsid dinosaurs for years. The idea that they held their forelimbs in a fully sprawled position, like lizards do, is no longer taken seriously, but authorities still debate whether these dinosaurs held their limbs in a straight, rhino-like posture or whether they slightly flexed them in an arrangement intermediate between the pillar and sprawling extremes. Since tracks of these dinosaurs are exceedingly rare, scientists must rely upon skeletal anatomy, and this is one area where not everyone agrees on how the bones in question should be put back together.
In order to get a new angle on this debate, Tirabasso created 3-D scans of the Cretaceous horned dinosaur Vagaceratops irvinensis (previously called Chasmosaurus irvinensis). From there he was able to re-articulate the bones in the three postures in question—sprawling, intermediate, and pillar—and make the partial dinosaur walk to see which mode of locomotion was the proper one. (Additionally, Tirabasso made fleshed-out models of the dinosaur, which can bee seen on the Canadian Museum of Nature Web site.) As had been suggested by previous studies of other horned dinosaurs, the intermediate posture was the best fit, meaning that Vagaceratops and its kin walked with its elbows slightly bent.
The scientific findings from this model were published in the journal Palaeontologia Electronica in 2007, but it was just last month that Tirabasso won the National Geographic Digital Modeling and Animation Award at the 70th annual Society of Vertebrate Paleontology meeting in Pittsburgh. Now, using this kind of approach, scientists can move beyond drawings and the bones themselves to study the articulations and movement of bones in ways previously impossible, and it will no doubt be extremely useful as paleontologists continue to study how ceratopsids and other dinosaurs moved.
September 16, 2010
Since the early days of paleontology, the posture of dinosaurs and the range of motion they were capable of have been contentious subjects for paleontologists. During the 19th century, especially, the general view of what dinosaurs would have looked like changed no less than three times, and investigations into how these animals moved continue to this day. Among the spate of recent studies on dinosaur flexibility, posture and motion is a new paper by Heinrich Mallison which used the Jurassic stegosaur Kentrosaurus to investigate some of the hypotheses surrounding this armored dinosaur.
Most of what we know about Kentrosaurus comes from the approximately 153-million-year-old Tendaguru Formation in Tanzania. It was there that the German paleontologist Edwin Hennig found numerous isolated bones and elements of disarticulated Kentrosaurus skeletons—in addition to the bones of many other dinosaurs—during the early 20th century; he was also lucky enough to find one partial skeleton of the stegosaur that was suitable for mounting. This specimen, reconstructed with sprawling limbs and a dragging tail, was on display at the Museum für Naturkunde in Berlin for decades. When it was taken apart to restore it in a more accurate posture in 2005, scientists made laser scans of each bone in order to create a digital restoration. It is this digital Kentrosaurus that formed the basis of Mallison’s new study—the closest thing a paleontologist has to a living dinosaur to examine.
In addition to its normal posture and range of motion, Mallison’s study looks at several controversial, little-studied ideas about this dinosaur and its kin. According to Hennig, Kentrosaurus had a squished, lizard-like posture and could not use its spiky tail for defense. In the 1980s, however, paleontologist Robert Bakker went to the opposite extreme, restoring stegosaurs with an erect posture that would have allowed them to pivot and swing their formidable tails at attacking predators. Additionally, Bakker proposed that Stegosaurus and its kin could have adopted a “tripodal” posture in which they reared back to rest on their tails, too, and were much more dynamic animals than envisioned by Hennig and other early 20th-century paleontologists.
Although Mallison stresses that the findings based upon his model are provisional, Kentrosaurus appears to have used different postures for different reasons. While walking, it would have held its limbs erect, but when threatened it was capable of flexing its forelimbs out into a sprawling position to help support itself as it swung its tail at an offending predator. In the latter circumstance, Kentrosaurus would have also been able to extend its neck to look backwards at an attacking dinosaur, though shifting position to keep a predator in view may have created blind spots that would have left this armored dinosaur vulnerable to multiple predators. As far as feeding was concerned, Kentrosaurus was indeed capable of rearing back to rest on its tail, though how often it would have done so—and what sort of food it would have been able to reach by doing so—is unknown. Overall, Kentrosaurus was not as stiff as Hennig proposed. Quite the contrary—this stegosaur was capable of altering its posture to suit a variety of circumstances, and it is likely that at least some of its relatives had similar abilities.
Mallison, H. (2010). CAD assessment of the posture and range of motion of Kentrosaurus aethiopicus Hennig 1915 Swiss Journal of Geosciences DOI: 10.1007/s00015-010-0024-2