November 1, 2010
How Vagaceratops Moved
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.
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I was under the impression that some trackways of ceratopsians had already been found, adding further credence to the idea that the forelimbs were held in an “intermediate” posture. Anyway, that does not diminish the great job these people have done in reconstructing the limb posture of an ancient animal.
Also, I have heard that there is still one scientist, I think based out of Wisconsin, who holds that ceratopsians held their forelimbs in a sprawling posture.
Anon – Yes, a few have been found. As I said in the post, ceratopsid tracks are rare. (See this reference for some of the only tracks to be published: http://www.jstor.org/pss/4523654) The tracks showed that the dinosaurs did not have a sprawling forelimb posture, but they did not resolve the issue of whether the forelimbs were bent or not. Hopefully paleontologists will find more trackways in the future to compare to the anatomical data which has already been collected.