# Paja Formation fossils in Colombia point to a 'Biotic Inflection' in an Early Cretaceous marine ecosystem

- Published: 2026-11-09 02:32 UTC
- Section: Life & Health › Biology & biochemistry
- Tags: Paja Formation, Early Cretaceous marine ecosystem, Biotic Inflection, Paja Biota, Gondwana, plesiosaurs, Villa de Leyva, marine food web, apex predators, paleohotspot
- URL: https://realtech.media/news/rt-aa82a42e1926e5f9827c38d3_paja_formation_fossils/

**McGill and CIP researchers reviewed the Early Cretaceous Paja Formation in Colombia, where older and newer marine lineages coexisted, and proposed a new macroecological pattern.**

![Paja Formation fossils in Colombia point to a 'Biotic Inflection' in an Early Cretaceous marine ecosystem](https://realtech.media/media/2026/11/3b0dbd19210c9cfb.webp)
*ScienceDaily*

Researchers from McGill University and the Centro de Investigaciones Paleontológicas (CIP) have published a review of the Lower Cretaceous Paja Formation of central Colombia in Frontiers in Ecology and Evolution. The authors, Hans Larsson and Dirley Cortés, synthesized biostratigraphic, paleoenvironmental, paleobiogeographic and paleoecological evidence. They wanted to assess whether the formation records unusual ecological and evolutionary dynamics during the faunal recovery after the Jurassic/Cretaceous boundary [1].

## Paja Biota and its food web

The fossils come from the area near Villa de Leyva, and most of the collected material is housed at CIP. The assemblage includes long-necked plesiosaurs, relatives of marine crocodiles, turtles, sharks and crustaceans. Together these animals form the Paja Biota [1].

In an earlier study, the same researchers reconstructed the feeding relationships among the animals of the Paja Biota. The analysis showed a complex food web with an unusually large variety of apex predators at its top. According to the authors, the formation preserves surviving Jurassic lineages alongside emerging Cretaceous groups.

## Biotic Inflection

On this basis Larsson and Cortés propose a concept they call a Biotic Inflection. It describes a turning point at which older groups approaching extinction coexist with newer lineages that are beginning to expand and diversify. The authors suggest that major evolutionary transitions may proceed this way, without the widespread destruction associated with mass extinctions [1].

They consider a combination of factors that may have shaped this ecosystem: greenhouse climate, sea-level change, nutrient flux, paleogeographic connectivity and oceanic anoxic events. They also point to new ocean connections between the eastern Pacific and the early Atlantic through the region that is now Colombia [1].

The review is cautious in its conclusions. The authors state that the Paja Formation cannot yet be designated a paleohotspot under strict modern criteria. They describe it as an exceptional Gondwanan marine system at the geographic and temporal intersection of several abiotic and biotic factors that drove biodiversity in the Early Cretaceous [1].

The researchers emphasize that more evidence is needed to establish how common the pattern was. They name additional fossil finds, more accurate estimates of fossil ages and comparisons with geological formations in other parts of the world as the next steps.

## Sources

1. [Frontiers in Ecology and Evolution](https://doi.org/10.3389/fevo.2026.1848892)
2. [ScienceDaily](https://www.sciencedaily.com/releases/2026/11/261106174535.htm)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-aa82a42e1926e5f9827c38d3_paja_formation_fossils/