Researchers at the Florida Museum of Natural History report that fossilized shark teeth can improve the dating of coastal sediments. The findings, published in the journal Palaeogeography, Paleoclimatology, and Paleontology, show that the ratio of strontium isotopes in these fossils records shifts in global coastal ecosystems over time. This approach adds a new layer of precision for paleontologists studying North American shores and can illuminate coastal changes that shaped environments along Canada and the United States alike.
Strontium is a chemical element found in water, soil, and rocks. In the oceans, isotope ratios evolve through cycles of land erosion, patterns of marine life, and deep sea volcanic activity. When preserved in fossil material, these shifts create a global signal that helps scientists determine the age of sea sediments and coastal deposits. The technique leverages the fact that different isotopes have distinct masses, allowing researchers to track past geographic and climatic shifts as reflected in the rocks and sediments that surround ancient fossil finds.
However applying this method to coastal fossils faced early obstacles. Freshwater inputs can disturb strontium composition, potentially masking the original signal, and dated material must resist physical and chemical changes to retain the initial isotope ratios. These challenges meant that practitioners needed materials with robust preservation to ensure reliable results, especially in settings where changing water chemistry could blur the isotopic record.
The study highlights that shark teeth possess an enamel-like coating that protects them from chemical alteration. This protective layer helps maintain the original strontium isotope ratios, making teeth reliable indicators for dating ancient beds and reconstructing coastal histories. Sharks have populated Earth for roughly 400 million years and shed thousands of teeth in their lifetimes, making their dentition among the most common sources of fossil material. Their abundance increases the chances of finding well-preserved specimens suitable for strontium analysis, particularly in Neogene coastal sequences across North America.
In the new work, scientists analyzed the teeth from two Florida sites linked to the Neogene period, spanning roughly 2.6 to 23.5 million years ago. Previously, the Montbrook site and the Palmetto Fauna were considered to be contemporaneous. The refined isotopic data show a difference of about 600,000 years between the two localities, refining the timeline for coeval faunas in the region. This level of resolution helps paleontologists align fossil assemblages with precise ages, improving the reconstruction of regional ecological shifts in late Neogene Florida and neighboring areas.
The results do more than fix ages. They offer new context for events in North America around five to six million years ago. For instance, the older Montbrook assemblage, around 5.85 million years, reveals a fauna that differs from the Palmetto assemblage dating to about 5.22 million years. Such a pattern supports the idea that the Great American Biotic Interchange began during the broader phase of oceanic and tectonic changes linked to the formation of the Panama Isthmus, enabling migrations between continents and reshaping regional ecosystems. The timing captured by shark teeth isotopes provides a tangible anchor for interpreting how coastlines and habitats shifted in response to these large-scale connections between landmasses.
Earlier researchers noted puzzling shifts in marine signatures and fauna during this interval. The isotopic dating offered by shark teeth helps explain these observations by delivering a coherent chronology that ties physical geography, ocean chemistry, and biogeography together. In Canada, the evidence complements coastal records from similar ages, helping build a more complete picture of late Neogene paleoenvironmental change across North America. In the United States, the approach enriches our understanding of how coastal ecosystems reorganized as climate patterns shifted and sea levels fluctuated, leaving behind a robust isotopic fingerprint in fossil teeth that can be traced across sites and regions.
Overall, the study demonstrates the value of fossil shark teeth as stable isotopic records for reconstructing past coastlines, climate dynamics, and biogeographic movements. The enamel protection and the widespread fossil record of sharks make their teeth especially useful for building a coherent timeline of Neogene coastal evolution. The results highlight how a single type of fossil remains can illuminate the interconnected story of geology, oceanography, and biology that shaped North American shores during a critical epoch in Earth’s history.