Scientists from McGill University and the Centro de Investigaciones Paleontológicas have identified an unusual evolutionary pattern in fossils from Colombia’s Paja Formation. The ancient marine ecosystem contains a remarkable mixture of Jurassic lineages that were approaching extinction alongside newly emerging Cretaceous groups, suggesting that major evolutionary transitions can happen without the widespread destruction typically associated with mass extinction events.
Researchers Hans Larsson and Dirley Cortés have introduced the term “Biotic Inflection” to describe this evolutionary turning point, when older groups in decline coexist with newer lineages beginning to expand and diversify. The researchers believe a combination of environmental factors enabled this unusual coexistence, including warm greenhouse temperatures, elevated sea levels, and nutrient-rich coastal waters. Additionally, the emergence of new ocean connections between the eastern Pacific and early Atlantic through the Colombian region likely created conditions supporting diverse marine life within the same ecosystem.
The Paja Formation near Villa de Leyva has preserved an exceptionally rich fossil record documenting this ancient ocean ecosystem. The site contains fossils of giant marine reptiles including long-necked plesiosaurs, marine crocodile relatives, turtles, sharks, and crustaceans. Previous research reconstructed complex feeding relationships among these animals, revealing an unusually intricate food web with an exceptional variety of apex predators at the highest ecosystem levels.
The researchers acknowledge that additional evidence is required to determine how common this evolutionary pattern may have been throughout Earth’s history. Further fossil discoveries, improved age estimates, and comparisons with geological formations worldwide will help establish whether similar transitions occurred elsewhere. The findings could represent a significant new framework for understanding how Earth’s biodiversity has changed over time, offering an alternative explanation for major evolutionary shifts beyond traditional extinction-driven models.
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