{"id":4446,"date":"2025-07-30T21:40:41","date_gmt":"2025-07-30T21:40:41","guid":{"rendered":"https:\/\/dornsife.usc.edu\/wrigley\/?p=4446"},"modified":"2025-07-31T19:12:46","modified_gmt":"2025-07-31T19:12:46","slug":"what-fossils-say-about-climate-change-migration","status":"publish","type":"post","link":"https:\/\/dornsife.usc.edu\/wrigley\/2025\/07\/30\/what-fossils-say-about-climate-change-migration\/","title":{"rendered":"Ancient Invasions, Modern Warnings: What Fossils Tell Us About Migration in Response to Climate Change Before Human Arrival"},"content":{"rendered":"\n\n\n\n\n \n \n\n\n\n\n\n\n\n
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2025 Wrigley Institute Graduate Fellow Priyanka Soni holds an endangered abalone specimen collected from Southern California in the 1900s. The specimen is currently part of the Natural History Museum of Los Angeles County’s special collection for educational purposes. Abalones have persisted for over 20 million years, but some species\u2014such as the black and white abalone\u2014are now critically endangered, according to the IUCN Red List (Nick Neumann\/USC Wrigley Institute).<\/p>\n\n\n\n<\/div>\n <\/div>\n \n

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Ancient Invasions, Modern Warnings: What Fossils Tell Us About Migration in Response to Climate Change Before Human Arrival<\/h1>\n\n\n<\/div>\n \n \n By<\/span>Priyanka Soni<\/strong>\n \n July 30, 2025<\/span>\n <\/div>\n<\/div>\n\n\n <\/div><\/div>\n\n \n \n\n\n\n\n\n\n\n
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From Shell Enthusiast to Scientist<\/b><\/h3>\n

Growing up near the ocean, I was fascinated by the small creatures I found in tide pools\u2014slow-moving snails, tiny <\/span>bivalves<\/span><\/a>, and the colorful shells used by hermit crabs. I\u2019d walk along the beach collecting <\/span>shell pairs,<\/span><\/a> wondering if they belonged to the same individual. It amazed me how these animals, which barely move at all, could be found across such a wide area\u2014from warm tropical waters to the colder shores of California.<\/span><\/p>\n

My curiosity grew deeper when I saw fossil shells trapped in the hills of Palos Verdes, far from the ocean. What were these marine animals doing inland and high above sea level? Why were the same shells I found on the beach also falling out of cliffs at Point Fermin?<\/span><\/p>\n

These early questions\u2014about where animals live, how far they can spread, and what happens to them over time\u2014sparked my journey from a beach-loving naturalist to a scientist studying ancient oceans.<\/span><\/p>\n

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Soni searches for Last Interglacial fossils near Point Fermin in the Palos Verdes Hills. She shows a hammer for scale, highlighting the thick fossil-rich layer visible in the cliff face. (Photo: Austin Hendy)<\/figcaption><\/figure>\n

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Why Mollusks Matter<\/b><\/h3>\n

When most people think about the ocean, they picture large open-water animals like sharks, whales, or dolphins. But there\u2019s an entire world of shell-bearing creatures that live along the coast and on the seafloor: mussels, clams, oysters, and more. These animals are part of what\u2019s called the <\/span>benthos<\/b><\/a>,<\/b> and they play a crucial role in marine ecosystems. You may even eat some of them in chowder or seafood pasta!<\/span><\/p>\n

But these animals are more than just food. They act as <\/span>ecosystem engineers<\/b>,<\/span><\/a> building habitats, cleaning the water, and serving as an important part of marine food webs, both as prey and as contributors to the structure of benthic communities. Some live attached to rocks, and others burrow in sand, from shallow tidepools to the deep sea. California alone is home to over <\/span>2,500 species<\/b><\/a> of these shelly animals!<\/span><\/p>\n

Despite their importance, we often overlook them\u2014especially the small, slow ones stuck to rocks. But as the climate changes, these slow ones are on the move too, and they may be the first to show us how our oceans are shifting.<\/span><\/p>\n

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Marine mollusk type specimens in the Malacology collection at the Natural History Museum of Los Angeles County. Type specimens are typical reference samples of a species and are used to help confirm the identity and characteristics of other samples. (Nick Neumann\/USC Wrigley Institute)<\/figcaption><\/figure>\n

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What Happens When the Ocean Warms?<\/b><\/h3>\n

Every species has a natural \u201c<\/span>geographic range<\/b><\/a>,\u201d an area with the right environmental conditions where it can survive and reproduce. But climate change is causing these ranges to shift. Warmer waters are pushing animals toward cooler regions, and we\u2019re seeing this in birds, mammals, and especially marine life.<\/span><\/p>\n

This process, sometimes called <\/span>\u201c<\/b>tropicalization<\/b><\/a>,\u201d<\/b>\u00a0is already happening along the California coast. Animals that used to live only in warm southern waters are now showing up farther north. This affects the <\/span>entire coastal ecosystem<\/b><\/a>, including the native species that already live there.<\/span><\/p>\n

But here\u2019s the challenge: modern scientists often have to wait and observe these changes in real time, then decide if a species is “<\/span>invasive<\/b><\/a>\u201d after it has already caused noticeable harm to native species. What if we could see this coming\u2014before it’s too late?<\/span><\/p>\n

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Looking to the Past for Clues<\/b><\/h3>\n

That\u2019s where my research comes in. Instead of waiting to see which species will move as the ocean warms today, I study what happened in the geological past, specifically during the <\/span>Last Interglacial Period<\/b><\/a>\u00a0about 120,000 years ago, when the global temperature was around 2 to 4 \u00b0C<\/strong><\/a> warmer than pre-industrial level<\/a>.<\/strong>\u00a0<\/span>Back then, much of coastal Southern California\u2014including most of what we now call Los Angeles\u2014was covered by the ocean. Believe it or not, scientists have found marine shell beds buried beneath places like the <\/span>La Brea Tar Pits<\/b><\/a> and even <\/span>downtown Los Angeles<\/b><\/a>!<\/span><\/p>\n

Over thousands of years, sea levels dropped and the land slowly rose through <\/span>geological uplift.<\/b><\/a> That\u2019s how these ancient seafloors were lifted above water, forming many of the flat coastal platforms we live on today. The shells that once sat on the ocean floor are now preserved in hillsides and cliffs and often exposed during the construction of highways, buildings, and <\/span>schools<\/b><\/a>\u2014a fossil snapshot of marine life from the past.<\/span><\/p>\n

These fossil beds tell us more than just what lived there. They help us spot \u201cancient invaders,” species that moved into new areas during past warming events. My goal is to figure out which species migrated and survived, which ones went extinct, and what enabled some to survive while others perished. Were they more adaptable? Did they outcompete native species? And can these ancient patterns help us predict what might happen in today\u2019s warming oceans?<\/span><\/p>\n

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Soni surveys a benthos (seafloor) ecosystem in shallow water off the coast of Catalina Island. She is looking for ancient invader species that are still alive today and appear to be shifting their ranges northward in response to climate change. (Photo: Bernadeth Tolentino)<\/figcaption><\/figure>\n

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How I Do This Research<\/b><\/h3>\n

My research combines <\/span>fieldwork, <\/span>museum studies, and <\/span>lab analysis to piece together the story of ancient ocean life.<\/span><\/p>\n