“Why did they think T. Rex stood with his tail on the ground?”

Photo Credit: Kasuga Sho

The Museum of Science in Boston boasts two life-size statues of the T. Rex. The one in the permanent dinosaur exhibit stands in the now-classic T. Rex pose: the predator in mid-stride with head forward, jaws open, and tail aloft to balance the weight of his massive torso.

Photo Credit: Kasuga Sho

The other, a prim sentry with tail planted firmly on the ground, stands outside in the sun, exposed to the elements, relegated to a life of greeting Museum visitors because he had the misfortune of being built according to an earlier understanding of dinosaur anatomy.

The two models stand in mute testimony to science’s ever-evolving vision of dinosaur physiology.

In most cases, only the bones of dinosaurs remain, so paleontologists must make educated guesses about the muscles, flesh, and other tissues that layer onto the bones to make up the complete creature. The classic method for making those guesses is to study the anatomy of creatures in the world today, and to use that anatomy to extrapolate what similar structures in dinosaurs would have looked like. That method, known as comparative anatomy, is what Richard Owen used to direct the design of the earliest dinosaur models created by Benjamin Waterhouse Hawkins for the Crystal Palace in 1851. (You can read more about the partnership between Richard Owen and Waterhouse Hawkins at the Victorian Web.)

Image Credit: Jacqueline Banerjee, 2009

Of course, comparative anatomy can lead to some colossal blunders. For example, Richard Owen surmised that since Iguanodon had teeth like a modern-day iguana only much larger, Iguanodon must have looked like an iguana, only much larger and with a horn on his nose (see photo on the left).

But thanks to new information in the fossil record, scientists now think he looked a bit more like this:

Iguanodon. Note the horn is now thought to be a thumb spike. (Image source: Q-files Encyclopedia.)
A more up-to-date artist’s rendering of the Iguanodon. Note the horn is now thought to be a thumb spike. (Image source: Q-files Encyclopedia.)

Images of dinosaurs change all the time as new information pours in. As you would expect, much of this new information comes from new fossil discoveries. Maybe it’s a more complete skeleton. Maybe it’s a bit of fossilized skin or evidence of feathers changing scientific opinion of what dinosaurs looked like. Or very rarely, it might be a dinosaur mummy with skin, scales, muscles, and beak intact like the 77-million year old duck-billed dinosaur discovered in 2002 in Montana.

Paleontologists today have new methods of gleaning information from the fossils they find as well. They can use microscopes to look at the cellular structure of the bones, helping them find evidence of growth rates and metabolism. CT scans let them to view previously inaccessible bones. And then there’s supercomputing, which allows them to map dinosaur movements or drape muscles, skin, and other soft tissues on a digital rendering of the bones to model the dinosaur’s appearance.

Which, incidentally, brings us to our answer about the T. Rex. In this April 2009 LiveScience article on how digital technologies are reshaping paleontology, author Charles Choi states that it is actually the size and shape of the muscles that determine how dinosaurs like T. Rex stood. If the muscles attached to the thigh bones of the T. Rex were short, he would stand upright, as the older T. Rex statue at the Museum of Science does. If those muscles were very long, as paleontologists now think they probably were, then T. Rex would walk with his torso forward, more like a bird.


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  2. […] If your child is like mine, you will have a fabulous time wandering through the park and pointing out all of the ways in which our knowledge of these beasts has improved since the 1930s. The Trachodon is now known as Edmontosaurus.  The T. Rex has lost all of its original fingers, but if you are lucky enough to spot a vintage postcard in the gift shop, you’ll see that it originally had three fingers, not two. The Stegosaurus is missing the spikes on its tail. The Dimetrodon isn’t a dinosaur at all, but more closely related to mammals. And of course, all of the dinosaurs’ stances are wrong. Some in subtle ways, some not so much. […]


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