This Saturday at the
Morrison Natural History Museum in
Morrison,
Colorado, we will be celebrating
Stegosaurus Day, in honor of Colorado's state fossil! (To learn more, click
HERE to
be redirected to the Facebook page of the Morrison Natural History
Museum!) So, in honor of
Stegosaurus Day, The Natural World is going to
have ourselves a little
Stegosaurus Week! Each day, we are going to be looking at a different aspect of
Stegosaurus, and tonight, we are going to be looking at the genus
Stegosaurus as a whole, and how our concept of
Stegosaurus has changed over time! Let's dive on in!
Stegosaurus was first discovered by famous
paleontologist Othniel Charles Marsh during the Bone Wars (a paleontological competition from Marsh and rival paleontologist Edward Drinker Cope) in the late 1800s, and was first described by him in 1877. When
Stegosaurus was first described by Marsh, he wasn't really sure what it was: he actually thought that it might be a
turtle-like creature, as you can see in his illustration from above! This reconstruction explains why
Stegosaurus has its name: covered, shingled, or roofed reptile. It wasn't until Marsh and his crew found other, more complete specimens of
Stegosaurus that he was able to figure out what the animal looked like with a greater degree of accuracy, which you can see in the reconstruction below.
The reconstruction above, while much closer to what we think
Stegosaurus looks like today than the first reconstruction, nevertheless has several key differences from today's reconstructions. One of the main issues that paleontologists face when reconstructing
Stegosaurus and its relatives from fossils is that the plates aren't attached to any bones. The plates are modified
osteoderms, used in many different animals to protect themselves from attack (a more extreme example of which can be seen in the close relatives of
stegosaurs, the
ankylosaurs). Like the osteoderms in other animals, such as the ankylosaurs, the osteoderms would sort of "float" in the skin, only attaching to the rest of the skeleton by means of softer tissues, softer tissues that don't typically fossilize. What paleontologists really needed was an articulated specimen of
Stegosaurus.
Well, that's exactly what paleontologist
Ken Carpenter got in the 1990s! Using this very complete and articulated specimen, Carpenter and his colleagues were able to solve a number of
Stegosaurus mysteries. For example: the exact placement of the plates. In Marsh's 1890s reconstruction above, you can see that he had positioned the plates in a single row running down the back. Later reconstructions by other scientists had been created with a double row of plates, which was proven to be correct by Carpenter's specimen. It was also shown that the plates alternated down the back, as opposed to the side-by-side reconstructions sometimes seen.
Another mystery that Carpenter's specimen was able to solve is the number and placement of the tail spikes. As you can see in Marsh's 1890s reconstruction above, he hypothesized that
Stegosaurus had four pairs of spikes, and that they pointed upwards at around 10-15 degrees from the vertical. Carpenter's specimen, coupled with further research, has shown that, to the best of our knowledge, no species of
Stegosaurus had that many tail spikes: in fact, from what we know, all species of
Stegosaurus had two sets of tail spikes, for a grand total of four. We also now know that, instead of the spikes being about 10-15 degrees from the vertical, they were almost certainly horizontal to the ground! This hypothesis is backed up by investigations into the flexibility of
Stegosaurus's tail: to successfully bring its tail spikes into play in the 10-15 degree arrangement,
Stegosaurus would have had to have a tail much like a scorpion, and all research done up to this point indicates that
Stegosaurus had nowhere near that much vertical flexibility in the tail. However, the horizontal reconstruction makes much more sense, as the tail seems like it would have had a great deal of side-to-side flexibility.
The final main difference between Marsh's 1890s reconstruction and our reconstructions of
Stegosaurus today lies in the way it held its tail and its neck. Due to the
Dinosaur Renaissance in the 1960s and 1970s led by
John Ostrom and his pupil
Robert Bakker, the perception of dinosaurs as lumbering failures changed dramatically to what it is today: not failures of evolution, but instead, a remarkable success that shaped the evolutionary course of the Earth for millions of years. This change in perception is reflected in how we think dinosaurs moved: we no longer think that they dragged their tails on the ground, barely able to keep their heads from dragging in the mud. Instead, we view them as much more nimble than we once thought. And while
Stegosaurus may not have been the nimblest of them all, you can clearly see how our ideas of how we think this animal moved around have changed over the years.
Want to learn more about
Stegosaurus and it's relatives? Well, check out the
Homebase for
Stegosaurus Week HERE to partake in more of the festivities!
