In 1990, fossil hunters in South Dakota made an exciting discovery. They found a dinosaur that turned out to be a big deal. It was a T. rex, one of the most famous dinosaurs, and it ended up in the Field Museum in Chicago. What made this find so special was the number of bones it had.
Hi, I’m Kate, and this is MinuteEarth. The dinosaur, now called SUE, was amazing because it was so “complete.” The fossilized skeleton had 250 out of the 380 bones that the living dinosaur once had. While this might not sound like a lot, most dinosaur fossils we find are just a few bone pieces or maybe a single tooth.
Finding complete dinosaur skeletons is rare because the process of becoming a fossil is pretty unlikely. When dinosaurs died, their bodies were often torn apart by other animals, their bones scattered by water, trampled by herds, and worn down by the weather. Because of this, most skeletons were broken up before they could turn into fossils.
Sometimes, skeletons managed to avoid all this damage and got buried mostly whole. But even then, they often ended up in places where fossilization couldn’t happen, leading to their decay. Any skeletons that did become fossils had to survive millions of years of changes in the Earth that could mess up entire rock layers. Even if a skeleton made it through all that, it still needed to be found at just the right time: when enough erosion had exposed the fossil, but not so much that it was worn away.
That’s why mostly complete skeletons like SUE’s are extremely rare. Certain conditions can help protect a dinosaur’s skeleton from being lost over time. For example, if a dinosaur was killed and buried at the same time—like during a volcanic eruption or a mudslide—these skeletons had a much better chance of staying intact. Also, smaller dinosaurs needed less sediment to be buried, making it easier for them to be covered completely. Lastly, more common dinosaurs, like the plant-eating Maiasaura, left behind more skeletons than rarer species, increasing the chances of finding complete fossils.
SUE was a T. rex—a big and not-so-common dinosaur—making it less likely to be found in such a complete state. However, it seems that a big flow of debris helped preserve it. This is lucky for us because the fossil is not only amazing to look at but has also taught us a lot about how T. rex looked, moved, and lived.
However, the special circumstances that allowed for SUE’s great preservation mean that it doesn’t really show how most dinosaurs died or how their remains were usually scattered and worn down. To learn about those things, we need to study the more common, less complete fossils. While finding SUE was incredible, it’s safe to say that discovering any dinosaur fossil, no matter how complete, is pretty amazing.
Imagine you are a paleontologist. Create a timeline that shows the process of fossilization, from the death of a dinosaur to the discovery of its fossil. Use drawings or digital tools to illustrate each step, and explain why complete fossils are rare.
Participate in a classroom simulation of a fossil excavation. Use tools like brushes and small shovels to uncover “fossils” buried in sand or clay. Discuss the challenges paleontologists face when finding and preserving fossils.
Based on what you’ve learned about SUE and other dinosaurs, design your own dinosaur. Consider what features it might have to survive in its environment. Present your dinosaur to the class and explain how it might become fossilized.
Play a matching game where you pair incomplete fossil pieces with images of complete dinosaur skeletons. This will help you understand how paleontologists reconstruct skeletons from partial remains.
Choose a dinosaur species and research its habitat, diet, and how its fossils were discovered. Create a presentation to share your findings with the class, highlighting any unique fossilization circumstances.
In 1990, fossil collectors in South Dakota discovered a dinosaur that turned out to be a significant find. Not only was it a T. rex, one of the most well-known dinosaurs, but it also ended up in Chicago’s famous Field Museum. The importance of this discovery was largely due to the number of bones it contained.
Hi, I’m Kate, and this is MinuteEarth. The dinosaur, now named SUE, was remarkable because of how “complete” it was: the fossilized skeleton had 250 of the approximately 380 bones that once made up the living dinosaur. While this may not seem like a large number, most dinosaur fossils we find are just a few bone fragments or a single tooth.
Complete specimens are rare because the process of becoming a fossil is unlikely to begin with, and the fossilization of an entire skeleton is even more improbable. When dinosaurs died, their bodies were often torn apart by predators and scavengers, their bones scattered by flowing water, trampled by herds of animals, and weathered by the elements. As a result, most skeletons were broken up before they had a chance to fossilize.
Occasionally, skeletons would escape this wear and tear and get buried mostly intact. However, even then, they often ended up in environments that were not conducive to fossilization, leading to decomposition. Any skeletons that did fossilize had to endure millions of years of geological changes that could disrupt entire layers of rock. Even if a skeleton survived all of this, it still needed to be discovered at just the right moment: when enough erosion had occurred to expose the fossil, but not so much that significant parts of it were weathered away.
Thus, even mostly complete skeletons like SUE’s are extremely rare. Certain conditions can help protect a dinosaur’s skeleton from being lost over time. For instance, if a dinosaur was killed and buried simultaneously—such as during a volcanic eruption or a mudflow—these skeletons had a much better chance of remaining intact. Additionally, smaller dinosaurs required less sediment to be buried, making them more likely to be covered completely. Lastly, more common dinosaurs, like the herbivorous Maiasaura, left behind more skeletons than rarer species, increasing the likelihood of finding complete fossils.
SUE was a T. rex—a relatively large and uncommon dinosaur—making it less likely to be found in such a complete state. However, it appears that a significant debris flow contributed to its preservation. This is fortunate for us, as the fossil is not only visually stunning but has also provided valuable insights into the anatomy, biomechanics, and daily life of a T. rex.
However, the unique circumstances that allowed for SUE’s exceptional preservation mean that it is not particularly representative of how most dinosaurs died or the conditions that typically scattered and weathered their remains. To learn about those aspects, we must study the more common, less complete fossils. While finding SUE was incredible, it’s fair to say that discovering any dinosaur fossil, regardless of its completeness, is quite remarkable.
Fossils – The preserved remains or traces of organisms that lived in the past, often found in sedimentary rock. – Scientists study fossils to learn about the types of plants and animals that existed millions of years ago.
Dinosaur – A group of reptiles that lived millions of years ago, some of which were very large and are now extinct. – The discovery of a new dinosaur species can provide valuable insights into Earth’s prehistoric ecosystems.
Skeleton – The internal framework of bones and cartilage in vertebrates that supports and protects the body. – The paleontologist carefully reconstructed the dinosaur skeleton to display in the museum.
Bones – The hard, rigid structures that make up the skeleton of vertebrates, providing support and protection for the body. – The archaeologist found ancient bones buried in the sediment, which belonged to a prehistoric animal.
Sediment – Particles of rock, soil, and organic material that are carried and deposited by wind, water, or ice. – Over time, layers of sediment can harden into rock and preserve fossils within them.
Erosion – The process by which natural forces like water, wind, and ice wear away rocks and soil. – Erosion can reveal fossils that were previously buried deep within the Earth’s surface.
Preservation – The process of maintaining something in its original or existing state, often used in the context of protecting natural or historical resources. – The preservation of fossils is crucial for scientists to study ancient life forms accurately.
Volcanic – Related to or produced by a volcano, often involving the eruption of molten rock, ash, and gases. – Volcanic activity can create new landforms and sometimes preserve the remains of organisms in ash layers.
Remains – The parts left over after other parts have been removed, used, or destroyed, often referring to the body parts of organisms. – The remains of the ancient forest were found beneath layers of volcanic ash.
Decay – The process of rotting or decomposing through the action of bacteria and fungi. – After an organism dies, its body begins to decay, but sometimes the conditions are right for fossilization instead.
