The season of dinosaur extinction

The exact moment when Earth’s most catastrophic mass extinction ended the dinosaurs’ reign 65 million years ago has remained a mystery. But now, an international team of paleontologists has pinpointed not just the year or decade but the exact season when the Chicxulub asteroid struck the Yucatán Peninsula: springtime.

Fish bones reveal seasonal timing

This discovery emerged from the study of remarkably preserved fish fossils that died within 60 minutes of the catastrophic impact. Researchers from Vrije Universiteit Amsterdam, Uppsala University, Vrije Universiteit Brussel, and the European Synchrotron Radiation Facility analyzed these ancient remains using cutting-edge X-ray technology and carbon isotope analysis. These techniques reveal seasonal growth patterns locked in bone structure.

Like tree rings recording yearly growth, fish bones preserve evidence of seasonal changes. The team discovered that bone cell density and volume were increasing but had not yet reached their annual peak. This is a telltale sign of spring growth. This timing detail provides crucial new insights into why certain species survived while others perished.

Paddlefish provide crucial evidence

The most compelling evidence came from a paddlefish fossil, a species that feeds exclusively on zooplankton. These microscopic organisms naturally fluctuate with the seasons, becoming more abundant as temperatures rise. Carbon isotope ratios in the paddlefish skeleton revealed that zooplankton populations were rising toward their summer peak but hadn’t arrived there yet – another spring indicator.

The seasonal timing matters beyond historical curiosity. Spring in the Northern Hemisphere corresponds to autumn in the Southern Hemisphere, potentially explaining regional differences in extinction and survival rates. Many animals’ biological clocks are finely tuned to seasonal changes, affecting breeding cycles, migration patterns, and food availability.

Implications for survival patterns

Birds and mammals that survived may have been in different life stages or locations that offered better protection. Species in reproductive cycles or caring for young might have been more vulnerable, while those in dormant phases or in different hemispheres could have had advantages. The discovery suggests that survival wasn’t random but may have been linked to seasonal behaviors and geographic distribution.

This research demonstrates how sophisticated fossil analysis techniques continue to reveal new details about ancient catastrophes. The preserved fish represent a unique snapshot. A snapshot of creatures that died so quickly their bones captured the exact environmental conditions of that fateful spring day.

Understanding the precise timing helps scientists model the cascading effects of the impact. The nuclear winter that followed would have been especially devastating for organisms expecting spring growth and reproduction. Instead of abundant food and warming temperatures, survivors faced darkness, cold, and ecosystem collapse.

The findings add another piece to the puzzle of how life recovered after Earth’s fifth mass extinction. By understanding exactly when and how the extinction unfolded, scientists gain insights into which traits and behaviors proved advantageous during the crisis. This knowledge is increasingly relevant as modern species face rapid environmental changes.

The research, published in Nature, showcases how even tiny preserved details in the fossil record can unlock major revelations about Earth’s history.

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