One of a pair of songs that I made especially for Stegosaurus Week! "Bone Wars, Marsh and Cope" to the tune of "Two Black Cadillacs" by Carrie Underwood. Below is the link to the song:
Here are the lyrics to the song:
Full Lyrics:
1800s, Morrison, a big find was made
"If Cope got a bone, Marsh lost," Dr. Bakker say
They devoted their life,
To get the most bones, each other they'd fight
Two rivals fighting over fossils in the dirt and grime
[Chorus:]
And the teacher, Lakes, he was a good man
And Marsh and Cope, they used to be friends
But then the two of them wanted the other to die
Bye, Bye bye, Bye
1,500 species they wrote down
Dug them all out of rock and from the deep ground
They both refused to work together on the same side
Bye bye, bye bye, bye bye
Bone Wars, Marsh and Cope
Eleven years ago researchers found some more fossil bone
123 years they'd been buried there for oh so long Matthew Mossbrucker, from the Morrison Natural History Museum
The site had been reburied, waiting for the right time, right time
[Chorus:]
Even now some of the fossils in rocks and time are still encased
Mystries and new species found in the Quarry
Learning new secrets from the grave
[Chorus:]
Are you diggin' the songs? Well, then check out our playlist below!
Here we will learn 8 Truths About the Stegosaurus.
This is the third video in our "Animal Truths" series. Make sure to check out the other two we have made so far, "8 Truths About the Mountain Lion" and "17 Truths About the Cheetah," below!
Stegosaurus lived in western North America during the Late Jurassic Period, about 150 million years ago (MYA). Today, we find its remains in the Morrison Formation, named after the tiny town of Morrison in Colorado. What was going on in Colorado at that time? What was the depositional environment like, the environment that laid down the sediment that would one day become the famed Morrison Formation?
Well, according to paleontologist Dr. Robert Bakker in an article about the re-discovery in 2002 of some old paleontological quarries (CLICK HERE TO LEARN MORE) in the Smithsonian Magazine, the environment was very much like the kind of environment seen in Uganda today: a “hot tropical woodland that was dry for most of the year.”
What about the animals, though? Dr. Bakker also said in the article that to “understand the Late Jurassic, you need to understand the common animals, which means Apatosaurus.” Most people are familiar with this massive animal: about 100 feet long (around the length of three school buses put end to end to end), and weighing around as much as eight African elephants, Apatosaurus was definitely a heavyweight of the Morrison biota!
What other animals were running around though? There are a great many dinosaurs, as well as many other animals, that were living in this area at that time, but in this post we are only going to look at one more: Camptosaurus and Allosaurus. All right, I lied. We’ll look at two more.
First off, we have Camptosaurus. To be honest, Camptosaurus doesn’t really look all that special. A small- to mid-sized ornithopod, Camptosaurus was only about fifteen feet long, and didn’t really appear to have any obvious defenses. However, discoveries of articulated Camptosaurus skeletons (indicating that the bones were fossilized were they were deposited, i.e. where the animal died, and weren’t washed together in a big mumble-jumble like at Dinosaur National Monument) in close conjunction with articulated Stegosaurus skeletons seems to indicate that these two herbivores liked to hang out together. But why? Why would they open themselves up to competition and potential conflict like that? Well, analysis of the brains and skulls of these two animals suggests that perhaps by hanging out together, the dinosaurian duo could avoid much deadlier conflict. Studies have shown that the sensory organs of Camptosaurus and Stegosaurus would have differed in very critical ways. The sense of Stegosaurus would have been akin to a rhinoceros, or perhaps myself as well (at least without my contacts), in that it would have had a pretty good sense of smell, but not very good vision. Camptosaurus, on the other hand, appears to have had quite acute vision, which has led to an interesting proposition by researchers: that Camptosaurus acted as a lookout for herds of Camptosaurus and Stegosaurus. If a predator was spotted (say, an Allosaurus or a Ceratosaurus), then Camptosaurus would have been able to alert the herd, and Stegosaurus would have been able to move to the forefront to defend them all against attack.
The last dinosaur that we are going to look at today is Allosaurus, a large, meat-eating theropod dinosaur. It occurs to me as I type this that I have done a very thorough job on Allosaurus before, so instead of typing this all again, I am going to be lazy and redirect you to another post that I did awhile back, entitled “23-Fact Tueday: Allosaurus.” Hidden within the post (but not too hard to find) are 23 Facts about Allosaurus. Yeah. Pretty much says it in the title. Anyways, check out that post to learn more about Allosaurus, as well as the rest of the Morrison ecosystem! And make sure to check back tomorrow, as we learn about stegosaurs from the rest of the world!
Want to learn more about Stegosaurus? Well, check out the Homebase for Stegosaurus WeekHERE to partake in more of the festivities!
In 2002, paleontologists from the Morrison Natural History Museum rediscovered an old paleontological dig site that had been missing since the late 1800s. One of many highly-contested sites of the so-called “Bone Wars” (a paleontological competition between rival paleontologists Othniel Charles Marsh and Edward Drinker Cope), this dig site, dubbed Quarry 10, has been the site of many very interesting discoveries, as has another Quarry nearby, Quarry 5.
Quarry 10 had long thought to have been destroyed. Fossil hunter Arthur Lakes had reportedly dynamited the dig site on Marsh’s orders, to prevent Cope from getting any fossil bones out of it. However, it looks like Arthur Lakes was a very good man, and did not actually dynamite the dig site. According to the MNHM paleontologists, it looks like Lakes, not wanting to destroy something that was potentially very valuable, decided to merely cover up the site with some rocks in order to prevent other people from coming across it.
Further excavations at the Quarrys have yielded a number of VERY interesting fossils, including, amongst others, some baby Stegosaurus footprints! Multiple blocks have been uncovered with the footprints of Stegosaurus at all different stages of development, everything from infants to adults. On some of the blocks, multiple age groups are found in close conjunction to each other, and sometimes are found going the same way. This seems to indicate that Stegosaurus would move in groups consisting on members of multiple ages, a very interesting discovery indeed!
Want to learn more about Stegosaurus? Well, check out the Homebase for Stegosaurus WeekHERE to partake in more of the festivities! You can also check out a song that I wrote to the tune of Carrie Underwood's "Two Black Cadillacs" to learn more about the Bone Wars, below!
The horns and frills of Triceratops. The tube-like crest of Parasaurolophus. The two crests of bone on Dilophosaurus. The sail on Spinosaurus. What function do these various bells and whistles that adorned these so-called "Terrible Lizards" serve? For years, most paleontologists assumed that they were for the sole purpose of combat, be it against predators, or the inter-specific variety. But now, more and more paleontologists are looking to birds to answer the question of functionality when it comes to these bony dinosaurian protuberances.
But what, specifically, about birds is it that is helping paleontologists figure out the purpose of these structures? It all boils down to an interesting phenomenon called "sexual selection." Most people are familiar with the term "natural selection." Popularized by Charles Darwin, natural selection essentially states that animals that are unfit to survive and reproduce in a given environment will die, and will be unable to add their genes to the genepool. (Certainly an oversimplified definition, but you get the picture.) Sexual selection, on the other hand, is a mode of natural selection, and introduced by Charles Darwin, as well. Sexual selection states that some individuals in a given population will be more likely to breed than other individuals will because they will stand out above the rest of the population. There are many ways of doing this, and birds are but one example. Horns and antlers are one instance: typically, if an animal has larger horns or antlers, they will be able to not only fend off predators better (i.e. natural selection), but they will be more likely to be able to fend off other males, and be more likely to be picked for the females (i.e. sexual selection). In many animals, form overcomes functionality in this endless quest for a mate, especially on insular (or island) populations. One of my favorite examples of this is the birds of paradise from New Guinea, as you can see in the video below.
That's all well and good, but how does that apply to the dinosaurs that we were talking about above? Well, for years, paleontologists assumed that dinosaurs like Triceratops and its relatives were using their horns and frills to fight off predators. Well, for Triceratops, that makes sense: with forward-facing horns and a two-inch thick frill, fighting off Tyrannosaurus doesn't seem that far out of the realm of possibility. However, upon examination of many of the other relatives of Triceratops (collectively called ceratopsian dinosaurs), you can see that, perhaps, not all of these frills and horns evolved to fight off predators. Below we have just one example. The picture you see is of a skull that below belongs to a ceratopsian dinosaur called Einiosaurus. As you can see, it does not seem anywhere near as well equipped for fighting off predators as Triceratops does. For example, its frill has a pair of massive holes in it. Furthermore, of its three horns, one points downwards, and two point towards the sky at about a forty-five degree angle. Unless Einiosaurus was being attacked by giant woodchuck-like, burrowing dinosaurs, or being dive-bombed by Tyrannosaurs in F-14s (as seen in Calvin and Hobbes!), it is difficult to see how Einiosaurus might have defended itself against its predators using its frill and horns. Another analogy I like to make is this: if you are a knight going into battle, you don't necessarily want to have a pair of giant holes in your shield, and your sword bent and pointing towards the ground.
So how does this all tie in to Stegosaurus? Well, a same sort of discussion has centered around Stegosaurus for many years. Were the plates used for defense? Or were they used for something else? First let's address the idea of defense. IN THE PREVIOUS POST, we discussed the thagomizer, the group of tail spikes, on the rear end of Stegosaurus. These tail spikes were almost certainly used to fend off enemies, and seemed to have done a very good job, too. So, if you think about it, if you were to cover a stegosaur in these spikes, it would be almost impervious to attack, right? Well, what's interesting is that, early in stegosaur evolution, many of these animals actually did have a lot more spikes than Stegosaurus did. As a matter of fact, the plates of Stegosaurus are nothing more than heavily modified spikes! Below, we have a few more primitive stegosaurs, all of whom demonstrate the fact that, prior to Stegosaurus, many of the plates were actually spikes!
So if the spikes were better than plates were at defending an animal against predators (which is the only logical conclusion that I think people can draw from the data at hand), then why did some of the stegosaurs change? For many years, paleontologists thought that they had a pair of answers to this interesting dilemma. The first was the idea that perhaps Stegosaurus used its plates as a thermoregulaton device. If the animal was too cold, then it could turn its body so that its plates faced the sun, maximizing its surface area that was facing the sun, and enabling it to warm up quicker. The reverse would have also worked: when it became to hot, Stegosaurus could turn perpendicular to the sun, minimizing the surface area that was absorbing the sun. Another theory was that Stegosaurus could flush blood to the plates, turning them a brighter color. This could have either frightened off enemies, or instead it could have been used to attract a mate.
These two ideas seem fairly good in theory: however, much like the skull of Einiosaurus, there are a few massive holes in this logic. If Stegosaurus used its plates as a thermoregulatory device, why do close relatives of Stegosaurus have very different plate shapes, or sometimes fewer plates altogether? If there was one design that these animals used to warm up or cool down, one would imagine they would all converge on the same design. But they didn't, which casts some serious doubt on the whole thermoregulatory idea.
There are two theories that seem to hold the most water today. The first one has the same general idea that the "flushing the plates full of blood" idea has: make yourself more noticeable, as these plates were very impressive looking structures. And, since they alternated down the back (SEE THE FIRST STEGOSAURUS WEEK POST HERE), then a side-on look of Stegosaurus would have been a very impressive sight, indeed! Other stegosaurs of the opposite sex would undoubtedly think so, and these plates probably served a large role in attracting a mate! Predators might have thought that the side-on view was impressive, too, and this might have caused them to think twice about attacking Stegosaurus. It also might have caused other members of the same species to back down, too, in cases where inter-specific combat might have otherwise come into play. As Matt Mossbrucker, the director and curator at the Morrison Natural History Museum likes to say, "think a skinny kid in a puffy coat."
Finally, the plates might have helped stegosaurs to differentiate from one another. This is a tactic often used in animals today (again, the birds of paradise and many other birds: see the last paragraph of our post on the cichlids of the Great African Rift Lakes HERE), and is thought to have been a tactic used by many extinct animals, as well. For example, the various horns and frills of the ceratopsian dinosaurs (like Triceratops and Einiosaurus that we were talking about before) are now thought by many paleontologists to have been used to tell each individual species apart, and its possible that that is what the stegosaurs were doing, too.
Want to learn more about Stegosaurus? Well, check out the Homebase for Stegosaurus WeekHERE to partake in more of the festivities!
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 today, we are going to be looking at the tail spikes on the tail of Stegosaurus, nicknamed the thagomizer! What were they used for? Did they actually use their tail spikes for defense? And how about that funky name: where did the term "thagomizer" come from? Well, learn those answers and more in today's post for Stegosaurus Week!
Remember IN THE LAST POST OF STEGOSAURUS WEEK when we mentioned paleontologist Ken Carpenter and his very complete and articulated Stegosaurus skeleton? Well, in 1993, when Carpenter was presenting his findings, he first used the term "thagomizer" to describe the tail and spikes of Stegosaurus. Without even knowing its backstory, it seems like a fitting name: but its true origin is even more interesting! For those of you who have enjoyed Gary Larson's fantastic "The Far Side" comic strip, then you may already know where we are heading with this! One of my favorite "Far Side" strips is the one above, and, interestingly, it is from this strip that Ken Carpenter got the name "thagomizer!"
Now, one question that has stumped paleontologists for years is, how were the spikes arranged on the thagomizer? Nowadays, we know that there were two sets of spikes, and they are thought to have been about 180 degrees from each other, forming a horizontal line. (For a more complete discussion, see the last post in our Stegosaurus Week series, entitled THE GENUS STEGOSAURUS THROUGH TIME.) But other questions stumped paleontologists, too. For example: what was the thagomizer used for? It definitely looks like a very apt defensive weapon, but for a long time, paleontologists had no clues to help them figure out whether defense was actually the answer.
One source of evidence that Stegosaurus and other stegosaurs were using their thagomizers to defend themselves is that many of the spikes have broken tips. Now, just because a fossil is broken, doesn't necessarily mean that it was broken during the animals life. Paleontologists can tell whether or not a bone was broken during the life of the animal by looking to see whether the bone shows any signs of healing. If the fossilized bone shows signs of "remodeling," then the bone broke during the life of the animal, and then started to heal while the animal was still alive. Following the death of an animal, if somehow a bone becomes broken, it's not going to heal: the animal is already dead! In a study that examined 51 tail spikes of Stegosaurus, researchers found that about 10% of these spikes had broken tips whose bone had started to grow back. So clearly, these spikes weren't just for show, and were actually being used for something.
The best evidence that paleontologists have right now that indicates that Stegosaurus was using its thagomizer to defend itself against predators is an Allosaurus tail vertebrae with a hole in it: a hole exactly matching the kind of hole that a thagomizer would have made! What's very interesting about this fossil is that, while damaged bone in the vicinity of the hole shows signs of healing (indicating that the Allosaurus survived, at least for a little while, following its encounter with Stegosaurus, and that the damage to the vertebrae was not post-mortem), the hole itself doesn't seem to have healed at all. This has caused some paleontologists to hypothesize that part of the tough outer sheath that would have surrounded the tail spikes in life, probably making them sharper and pointier, of a Stegosaurus became stuck in the tail vertebrae, remaining lodged within the tail vertebrae of that particular Allosaurus, until the animal died!
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.
