Sara Moore | Science Editor
On Sept. 25, The College of Wooster welcomed Dr. Elizabeth C. Sibert from the Woods Hole Oceanographic Institution (WHOI). Sibert’s talk, titled “A Microfossil History From the Bottom of the Sea: Sharks, Fish, Mass Extinctions and 85 Million Years of Global Change,” discussed what scientists have learned about Earth’s history from fossil records. This lecture was presented by the earth science and biology departments as part of the Ocean Discovery Lecture Series, which the U.S. Science Support Program funds.
Sibert began her talk by discussing her work in the Paleo (Biological) Oceanography: Fossil Ichthyoliths, Sedimentary History and Ecological Study (Paleo-FISHES) Lab at the WHOI, where she has worked for the past two years. She has worked on board the JOIDES Resolution, a research vessel that drills into the ocean floor to collect and study core samples. Sibert highlighted the ability for students to be involved in science and the arts, being a professional circus acrobat herself. She also discussed the importance of accessibility in science, technology, engineering and math (STEM), showing images of her lab, which was designed to be accessible.
The primary research question of Sibert’s work is: “How does the ocean and marine life work in the past, present and future?” Sibert studies this question through the lenses of biology, oceanography and geology. While fish are often overlooked in favor of charismatic megafauna, they are the planet’s most diverse group of invertebrates. The $130 billion fishing industry supports the livelihoods of over 40 million people.The type of fish present within an ecosystem tells scientists about its production, structure and evolution. The environment around fish impacts them, so scientists measure ocean conditions like temperature, salinity and pH to determine how the ecosystem functions. Since fish are only one part of their ecosystem, scientists also consider the plankton living within an area to determine the health of the food chain. Plankton function as the base of the food chain, with their presence in an environment determining which fish species inhabit that ecosystem. Through the ocean’s abundant fish fossils scientists are able to learn about the evolution of marine environments.
In her research, Sibert works with ichthyoliths, a type of microfossil from fish and sharks. These fossils are resistant to disintegration and are the most abundant vertebrate fossils on the planet. There are two types of ichthyoliths: dentacles, the dermal scales of sharks, and fish teeth, which mostly come from ray-finned fish. Other fossils, such as scales and otoliths (ear bones), are less prevalent in Sibert’s research.
Sibert’s research has revealed a lot about the ocean’s history. For example, the Cretaceous-Paleogene extinction event, which killed the dinosaurs, also had a massive impact on marine productivity. Numerous marine predators and over 90% of calcareous plankton went extinct. Despite this, fish became more abundant and increased in average size. Scientists hypothesize that as the ocean temperatures rose, the ecosystem became more efficient, possibly causing this spike in population. This is a good sign today, as ocean temperatures are rising due to global climate change. Other marine life may be impacted, but based on fossil records, fish will continue to survive and even thrive in their changing environment.
Sibert’s team also uncovered an apparent mass extinction of sharks 19 million years ago. This is the largest-known extinction event in the 400 million years of shark evolution, as over 70% of species were lost. This was the only change in the shark-to-fish ratio since the Cretaceous-Paleogene extinction event. The scientists discovered this because there were fewer dermal shark scales from this time compared to any other point in the fossil record. This was not an issue of preservation, as there are fish teeth and other fossils from this period. Additionally, there were no obvious climatic or catastrophic drivers for change during this time. Scientists have found that the decrease in shark populations resulted in an increase in the populations of other large marine animals like whales. Once shark populations rebounded, sharks became more migratory, which is how we understand their behavior today. More research is being done to determine what caused this extinction event.
Sibert ended her lecture by highlighting how ichthyoliths tell scientists how species reacted to environmental changes in the past so they can predict what will happen when changes occur in the future. After a brief question and answer session, attendees were invited to continue the conversation with her over a catered lunch from Chipotle.
For more information on Sibert’s research, please visit https://elizabethsibert.com/