Something fundamentally rewired the ocean's predator ecology
Hace 19 millones de años, en el Mioceno temprano, los tiburones estuvieron al borde de la desaparición en un evento de extinción que la ciencia apenas comienza a comprender. Un estudio liderado por la Universidad de Yale, publicado en la revista Science, revela que sus poblaciones colapsaron más del 90 por ciento sin que ninguna catástrofe climática conocida lo explique. Este hallazgo, obtenido a través de fósiles microscópicos en sedimentos del fondo marino, nos recuerda que los grandes predadores del océano son más frágiles de lo que imaginamos, y que las consecuencias de perderlos pueden resonar durante millones de años.
- Un colapso silencioso borró más del 90% de los tiburones del planeta hace 19 millones de años, un evento dos veces más devastador para estos animales que el impacto del asteroide que acabó con los dinosaurios.
- Lo más inquietante es que no hay culpable claro: ninguna crisis climática ni extinción terrestre conocida coincide con esta catástrofe marina del Mioceno temprano.
- Las investigadoras Elizabeth Sibert y Leah Rubin descubrieron el evento casi por accidente, analizando escamas y dientes microscópicos preservados en núcleos de sedimento del fondo oceánico profundo.
- Los tiburones que sobrevivieron jamás recuperaron su diversidad anterior, y la variedad que existe hoy es apenas una fracción de lo que poblaba los mares antes del colapso.
- Este registro del pasado profundo se convierte ahora en una advertencia: si los grandes predadores oceánicos continúan declinando hoy, las consecuencias podrían ser igualmente profundas y duraderas.
Hace 19 millones de años, los océanos vivieron una transformación silenciosa y devastadora: los tiburones casi desaparecieron del planeta. Un estudio publicado en Science documenta este evento catastrófico del Mioceno temprano, en el que las poblaciones de tiburones se desplomaron más del 90 por ciento y su diversidad morfológica cayó más del 70. Lo que sobrevivió nunca se recuperó del todo. La diversidad actual de tiburones, concluye el estudio, es apenas una sombra de lo que existía antes de esta antigua calamidad.
Las investigadoras Elizabeth Sibert, de Yale, y Leah Rubin, del College of the Atlantic, llegaron a este descubrimiento por un camino poco convencional. En lugar de depender de los registros fósiles tradicionales —limitados a depósitos de aguas poco profundas—, analizaron restos microscópicos en núcleos de sedimento del fondo marino profundo: escamas y dientes diminutos acumulados durante 40 millones de años. Esa resolución reveló un colapso que había pasado casi inadvertido en la paleontología.
Lo que hace aún más desconcertante al evento es su aparente independencia de cualquier catástrofe global conocida. El Mioceno temprano no estuvo marcado por grandes convulsiones climáticas ni extinciones terrestres. Sin embargo, transformó radicalmente la ecología de los predadores del océano abierto, afectando con especial severidad a los tiburones pelágicos. En perspectiva, este colapso fue dos veces más grave para los tiburones que el impacto del asteroide que extinguió a los dinosaurios hace 66 millones de años, cuando en los mares nadaban aproximadamente diez veces más tiburones que hoy.
Para la conservación contemporánea, esta historia antigua tiene un peso concreto. El estudio ofrece una línea de base de 40 millones de años contra la cual medir los cambios actuales en las poblaciones de tiburones. Comprender qué ocurrió entonces —y que sus efectos fueron profundos y duraderos— ayuda a anticipar lo que podría suceder si los grandes predadores del océano siguen desapareciendo hoy.
Nineteen million years ago, the oceans underwent a transformation so severe that sharks nearly vanished from the planet. A new study published in Science documents this catastrophic event—one that remains mysterious because it appears to have occurred without any known climate crisis or mass extinction on land to explain it. Researchers from Yale University and the College of the Atlantic discovered that shark populations plummeted by more than 90 percent during the early Miocene, while their morphological diversity collapsed by more than 70 percent. The sharks that survived never fully recovered. Today's shark diversity, the study concludes, represents only a fraction of what existed before this ancient calamity.
Elizabeth Sibert and Leah Rubin uncovered this extinction event using an unconventional approach. Rather than relying on traditional fossil records—which tend to capture only shallow-water deposits and offer limited insight into deep-ocean life—they examined microscopic remains from deep-sea sediment cores. These tiny fossils, shed scales and teeth from sharks and other fish that accumulate naturally on the ocean floor, provided a window into shark populations spanning the last 40 million years. The resolution this method offered revealed a dramatic collapse that had gone largely unnoticed in the paleontological record.
What makes this extinction particularly puzzling is its apparent independence from any known global catastrophe. The early Miocene was not marked by the kind of climate upheaval or terrestrial extinction that might explain such a dramatic loss of marine life. Sibert, who discovered the extinction almost by accident while analyzing the data, emphasizes that the event transformed the fundamental ecology of open-ocean predators. The die-off was especially severe for sharks living in the pelagic zone—the open ocean—compared to those in coastal waters.
The scale of this ancient collapse dwarfs even the famous extinction event that killed the dinosaurs. Sixty-six million years ago, an asteroid impact wiped out three-quarters of all plant and animal species on Earth, including most sharks. Yet the extinction event 19 million years ago was twice as severe for sharks specifically. At that time, roughly ten times more sharks patrolled the oceans than exist today, making the subsequent loss even more staggering.
The mystery deepens because no obvious culprit emerges from the geological record. Sibert notes that this interval in Earth's history is not known for any major upheaval or transformation—yet it fundamentally altered what it meant to be a large predator in the open ocean. The event essentially reset the trajectory of shark evolution, laying the foundation for the major shark lineages that would come to dominate modern oceans.
For contemporary conservation efforts, this ancient history carries weight. Leah Rubin, now at the State University of New York, frames the current decline in shark populations as concerning, but she emphasizes that understanding this deep-time context is essential. The study provides a baseline against which to measure modern shark population changes over the past 40 million years. That perspective matters because it helps scientists anticipate what might follow if today's large ocean predators continue to decline. The consequences of losing major predators from the ocean ecosystem remain incompletely understood—but this ancient extinction suggests the effects could be profound and long-lasting.
Citas Notables
This interval is not known for any major change in Earth's history, yet it completely transformed what it meant to be a large predator in the open ocean— Elizabeth Sibert, Yale University
Understanding this context is a vital first step for comprehending what consequences might follow the dramatic declines of these major predators in modern times— Leah Rubin, State University of New York
La Conversación del Hearth Otra perspectiva de la historia
How did researchers even know to look for this extinction event? It seems like something that would be easy to miss.
They were analyzing deep-sea sediment cores—essentially drilling down into the ocean floor and examining layers of accumulated material. Sibert has said she discovered it almost by accident while working through the data. The traditional fossil record had missed it because most fossils come from shallow-water deposits, which don't tell the whole story.
So the tiny shark teeth and scales in these cores revealed something the bigger fossils couldn't?
Exactly. Those microscopic remains accumulate naturally on the ocean floor over millions of years, creating a continuous record. When you look at the density and diversity of these microfossils, you can see the population crash clearly—a 90 percent drop in abundance.
But here's what I don't understand: if this was such a massive event, why don't we see evidence of some climate disaster or environmental trigger?
That's the real puzzle. There's no known global climate event, no asteroid, no obvious cause. The Miocene was relatively stable. Yet something fundamentally rewired the ocean's predator ecology. It's one of those moments in Earth's history where the cause remains hidden.
Does this tell us anything useful about what's happening to sharks now?
It provides context, which is crucial. We know sharks can experience catastrophic declines and take millions of years to recover—if they recover at all. Understanding that ancient collapse helps us think seriously about what modern population losses might mean for ocean ecosystems over the long term.