March 5th

Are ‘Phony Bones’ For Real?

When dinosaurs like Spinosaurus are missing skeletal elements, paleontologists can use a number of clues to help reconstruct the ancient beasts. But, as discussed yesterday, these methods are more than mere guesswork. There are several lines of thought that can help us recreate long extinct animals with reasonable certainty.

AMNH.org
AMNH.org

The first is our tetrapod heritage. All vertebrates on our planet are descended from fish with bilateral symmetry. One side of our skeleton is a mirror image of the other side and we tend to possess features in pairs–two legs, two arms, two eyes, etc. So if you dig up a dinosaur and you find a right leg, you can create a mirror image and you’ve got a left leg as well. This is important because almost no dinosaurs are found complete in the way Jurassic Park portrayed, with the animals fully formed in the ground. Some specimens are exquisitely preserved and anatomically intact, but most are disarticulated and fragmentary.

Luckily, many dinosaurs follow a standard body plan. Take the ceratopsians–the horned dinosaurs. Their frills and horns vary wildly from species to species, but the basic quadrupedal body plan is the same. The same goes for the crested hadrosaurs–commonly called ‘the duck-billed’ dinosaurs. There are a number of families of sauropod dinosaurs, but even there, the basic structure of the animals is the same. Perhaps a few of the bones could be slightly revised after further discovery–a wider flange here, a shorter chevron there–but the basic visual impact of a dinosaur remains.

Skulls, which are exceedingly rare, can be a trickier business. Since these are literally the face of dinosaurs, when skulls are substituted until a legitimate specimen is found, some skeletal mounts can seem radically changed. But even here, things aren’t wildly wrong. Let’s take the case of the Apatosaurus/Brontosaurus skull. Since scientists didn’t have a proper skull until a few decades ago, the famous mounts in natural history museums had sculpted skulls. These were made to resemble a cousin sauropod, Camarasaurus. So yes, the skull was an approximation. Yes, the skull looked very different when correctly assigned. Data about lifestyle and diet were updated. But the skull wasn’t a million miles off the mark (I’m sure some anatomists and purists might find this idea repugnant, but bear with me. In a general sense, these are both herbivorous skulls, not bloodthirsty killers.) Although the skulls were different, the scientists of the day were using their best judgment to create an image of the past for the public that was not too far from the truth.

Which leads us back to Spinosaurus. Most dinosaurs that are partially reconstructed don’t draw much criticism–though there is a great deal of murmuring about skeletons that ‘aren’t real’ in museums. This is not an accurate criticism. Every skeleton is a reconstruction of some sort, and exhibits are best when they are transparent about what has been sculpted, scanned, or is actual fossil. But sometimes, as in the case of Spinosaurus, there is no other way to resurrect the animal in three dimensions.

There is scientific value to this approach as well. Mounting actual bones makes study difficult, and also restricts the kind of freedom that modern exhibits relish. The Barosaurus in New York City’s American Museum of Natural History, rearing up to 60 feet tall on its hind legs would be an impossible exhibit without the use of casts. Casts also allow real specimens to be on display in many places at once–even if the actual fossils are kept in just one. Although these are facsimiles, the actual bones are no less real. You’re seeing a real dinosaur. Just not real fossils.

This is not to say there is not value in seeing the actual bones. There is nothing better. But cries of “fake” are often misdirected when it comes to fossil skeletal mounts. But what about Spinosaurus? The dinosaur was full of so many revelations, so astonishingly different from what was previously supposed, and so unprecedented in terms of scale and strangeness that many people (understandably) questioned the team’s findings.

While the debate over the reconstruction continues, audiences around the world can enjoy the “skeleton” of Spinosaurus in their museums and in their imaginations. And after all, isn’t that the most important goal of our dinosaur skeletal mounts–to stoke our imaginations into picturing a world we’d otherwise never get to see? Our best guesses will always fall short of the true majesty of the Mesozoic.

Tomorrow, we’ll begin a survey of the other famous ‘saurians’ that existed during the ‘Age of Reptiles.’ Until then, share your favorite dinosaur skeletal mounts with us on Facebook and Twitter using the hashtag #TDIDinos.

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