Welcome to the fascinating realm of Oversized Geology, where we delve into the world of dinosaurs and other prehistoric creatures that are too large to be housed elsewhere. Today, we are joined by Joyce Havstad, who holds the intriguing title of Philosopher in Residence at the Field Museum. Her role involves exploring how we understand and categorize the natural world through our senses.
One of the key concepts Joyce has explored during her time at the Field Museum is the idea of holotypes. A holotype is a single physical specimen that serves as the definitive example of a species. It acts as a benchmark against which other specimens are compared to determine if they belong to the same species. This concept is straightforward when dealing with living organisms, but it becomes more complex when we consider the fossil record, where complete skeletons are often unavailable.
To illustrate this challenge, let’s consider the historical development of the meter as a unit of measurement. Scientists once needed a universal standard for measuring distance, which led to the creation of the meter. After much debate, it was defined as one ten-millionth of the distance from the Equator to the North Pole. To ensure consistency, a prototype meter bar was created in 1889, made of platinum and iridium, and kept at a specific temperature.
Now, imagine trying to measure a meter if you only had fragmented pieces of that meter bar scattered around a room. This is similar to the situation paleontologists face when trying to identify species from incomplete fossil remains.
Let’s take a closer look at the Brachiosaurus, a dinosaur whose holotype was discovered by Elmer Riggs on July 4, 1900. At the time, it was considered the largest dinosaur known. The holotype consists of seven vertebrae, the sacrum, two caudal vertebrae, four dorsal ribs, a coracoid, humerus, ilium, and a femur. This represents about 20% of a complete skeleton, yet it remains the most complete Brachiosaurus specimen available.
One of the defining characteristics that led Riggs to identify Brachiosaurus as a new species was the unusual ratio between its femur and humerus. Unlike most sauropods, the Brachiosaurus had a longer humerus than femur, resulting in shorter hind legs and a tilted posture. This adaptation suggests that Brachiosaurus likely fed on tree foliage rather than grazing on grass, much like a giraffe.
Such insights demonstrate the detective work paleontologists engage in, piecing together clues from partial skeletons to make informed conclusions about prehistoric life. Riggs’s discovery of Brachiosaurus as a distinct species was a significant achievement, highlighting the importance of holotypes in understanding the diversity of life on Earth.
The study of holotypes and the challenges of working with incomplete fossils offer a glimpse into the meticulous work of paleontologists. By critically examining the available evidence, scientists like Elmer Riggs have made groundbreaking discoveries that continue to enrich our understanding of the ancient world. The story of Brachiosaurus serves as a testament to the excitement and satisfaction that comes from uncovering the mysteries of our planet’s past.
Engage in a hands-on workshop where you will examine replica fossils and attempt to identify holotypes. Discuss with your peers how these specimens can be used to define a species, and consider the challenges faced when dealing with incomplete fossils.
Work in groups to reconstruct a dinosaur skeleton using fragmented fossil pieces. Use critical thinking to hypothesize which pieces fit together and what the complete dinosaur might have looked like. Present your findings to the class.
Participate in a debate about the historical development of measurement standards, such as the meter. Discuss how these standards relate to the challenges of defining holotypes in paleontology, drawing parallels between the two fields.
Conduct a detailed case study on the Brachiosaurus. Analyze the unique features that distinguish it from other sauropods and explore how these features influenced its classification as a new species. Share your insights in a written report.
Join a philosophical discussion led by a guest speaker, exploring the complexities of species classification in paleontology. Reflect on how our understanding of the natural world is shaped by the evidence available to us and the role of holotypes in this process.
Sure! Here’s a sanitized version of the transcript:
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♪ We’re in Oversized Geology, surrounded by dinosaurs and other prehistoric life that is too big to go elsewhere. We’re with Joyce Havstad, who has a fascinating job title. What is your role at the Field Museum? People call me the Philosopher in Residence. All knowledge must come through the senses.
What are some concepts that you’ve pursued in your post-doc residency at the Field Museum? (Joyce) Holotypes. Holotypes are the individual physical specimens that bear the name for and act as the exemplar of a whole species. It’s the basis, the gold standard for—yeah, it’s the universal standard. It’s the yardstick that you measure other organisms against to see whether they match.
It seems to make sense and would be easy with a massive library of millions of comparable specimens if you find something existing today. But what about the fossil record, where you might not have a complete skeleton? How do you compare species?
Do you know about the meter bar? Back when science was starting, scientists realized we needed a universal standard of measurement, a distance that we could agree on. That was the meter. They debated about a meter’s length and decided it would be one ten-millionth of the distance between the Equator and the North Pole. Then they had to figure out that distance, sending some individuals out who spent 10 years measuring between a belfry in Dunkirk and a castle in Catalonia. Eventually, everyone realized we needed an official bar that was the prototype meter. In 1889, they made a bar of 90% platinum and 10% iridium, with two lines on it, kept at the temperature of melting ice. The distance between the lines at that temperature is a meter.
So you asked about paleontology. Imagine if, when a scientist wanted to know, “How long is a meter?” and someone was like, “It’s right there,” but they only had pieces of the meter stick. It was chunked up and scattered around the room. That’s the kind of situation paleontologists are dealing with when trying to figure out what specimen represents a species, like Brachiosaurus.
We’re standing in front of the holotype of Brachiosaurus. It was declared the largest dinosaur known when it was discovered on July 4, 1900, by Elmer Riggs. So what do we have of it? We have seven vertebrae, the sacrum, two caudal vertebrae, four dorsal ribs, a coracoid, humerus, ilium, and a femur.
This is the femur? Yes. Is that about 14 bones of the Brachiosaurus? It’s about 20% of a whole skeleton. It’s still the most complete Brachiosaurus specimen. Can you imagine what Elmer Riggs was thinking? Was his first thought, “I’ve discovered a new species!”? And afterwards, how did he determine this was the holotype of a new species?
One interesting aspect of Brachiosaurus that was definitive for Riggs in thinking this was a unique sauropod is the information we get because we have the femur and the humerus. This humerus is huge and long. Guess what? The humerus is longer than the femur.
So it had shorter legs in the back? Yes. Think about what other animals that looks like. That’s a great question. Shorter legs and longer arms would tilt you up. So normal sauropods—like a giraffe! The most closely related species to Brachiosaurus are actually named after a giraffe.
So this wasn’t evenly balanced. It was tilted up, with a long neck. That tells us about its ecology too—likely feeding on tree foliage and not grazing on grass. There’s so much to learn from the ratio between the femur and humerus.
Okay! That’s—I’m impressed with how I drew that conclusion. I was right, not that I accomplished anything. I think it’s exciting to look at a little information and infer as much as possible, critically examining the small bits you have. That’s the sort of detective work that paleontologists do with even partial skeletons and working with these holotypes.
That’s the kind of characteristic feature that would give someone a solid argument—like Riggs—a good argument for thinking, “This is its own species, a holotype. I’ve discovered a new species.” And it’s the largest dinosaur ever. I bet he felt good. He was excited.
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Dinosaurs – Extinct reptiles that lived during the Mesozoic era, known for their diverse sizes and forms. – The study of dinosaurs provides insights into the evolutionary history of vertebrates.
Paleontology – The scientific study of life in the geological past, particularly through the analysis of fossils. – Paleontology has revealed much about the Earth’s history and the organisms that once inhabited it.
Holotypes – A single physical example of an organism, known as the type specimen, upon which the description and name of a new species is based. – The holotype of the newly discovered dinosaur species was carefully preserved in the museum’s collection.
Fossils – Preserved remains or traces of organisms from the remote past, typically embedded in rock. – Fossils provide crucial evidence for understanding the evolutionary history of life on Earth.
Species – A group of organisms that can interbreed and produce fertile offspring, sharing common characteristics and genetic heritage. – The classification of species is fundamental to biological taxonomy and evolutionary studies.
Geology – The science that deals with the Earth’s physical structure and substance, its history, and the processes that act on it. – Geology helps scientists understand the formation of mountains, earthquakes, and the distribution of natural resources.
Measurement – The process of obtaining the magnitude of a quantity relative to an agreed standard. – Accurate measurement is essential in experiments to ensure reliable and reproducible results.
Evidence – Information or data that supports or refutes a hypothesis or theory. – The fossil record provides compelling evidence for the theory of evolution by natural selection.
Adaptations – Inherited characteristics that enhance an organism’s ability to survive and reproduce in a particular environment. – Adaptations such as camouflage and mimicry have evolved in many species to avoid predation.
Discoveries – The act of finding or learning something for the first time, often leading to new knowledge or understanding. – Scientific discoveries in genetics have revolutionized our understanding of heredity and disease.
