# McGill team proposes 'Biotic Inflection' from Colombia's 120-million-year-old Paja marine fossils

- Published: 2026-11-05 00:42 UTC
- Section: Life & Health › Biology & biochemistry
- Tags: Paja Formation, Paja Biota, Early Cretaceous marine ecosystem, Biotic Inflection, Colombia fossils, plesiosaurs, apex predators, Gondwana, paleohotspot, McGill University
- URL: https://realtech.media/news/rt-bf7ebc1343fd9bedc0466db8_mcgill_team_proposes/

**Fossils of the Early Cretaceous Paja Formation in Colombia show a complex food web with many apex predators. The authors suggest major evolutionary shifts can occur without a mass extinction.**

![McGill team proposes 'Biotic Inflection' from Colombia's 120-million-year-old Paja marine fossils](https://sgzwpqqelzmajkcubgkl.supabase.co/storage/v1/object/public/rt-media/2026/11/d891e55e52403cc7.jpg)
*Mark Healey from Brough, UK, Wikimedia Commons, CC BY-SA 2.0*

Dirley Cortés and Professor Hans Larsson of McGill University's Department of Biology, working with the Centro de Investigaciones Paleontológicas (CIP) in Colombia, have reviewed the evidence from the Early Cretaceous Paja Formation near Villa de Leyva, central Colombia. The review, published on 15 May 2026 in Frontiers in Ecology and Evolution, concerns a marine ecosystem about 120 million years old. [1]

## The Paja Biota and its food web

CIP houses most of the formation's fossils. According to Cortés, they include giant marine reptiles such as long-necked plesiosaurs and relatives of marine crocodiles, as well as turtles, sharks and crustaceans. Together these animals formed the Paja Biota, which he described as one of the most ecologically complex marine communities found to date. [1]

In an earlier study, the researchers estimated the food web of the Paja Biota, the network of feeding relationships among its animals. They found it to be among the most complex to have evolved, with a high diversity of apex predators. [1]

The assemblage combines Jurassic survivors with emerging Cretaceous predators. Larsson said that environmental factors known to promote ecological complexity coincided with ancient lineages that were about to disappear, while new groups were beginning to flourish.

## Biotic Inflection and open questions

The authors examined how paleogeographic connectivity, greenhouse climate, sea-level change, nutrient flux and oceanic anoxic events may have interacted with ecological escalation, diversification, trophic networks and lineage survival. They suspect that greenhouse temperatures, high sea levels and nutrient-rich coastal waters supported the biodiversity and the biological transition. New marine connections between the eastern Pacific and the early Atlantic through what is now Colombia were probably part of this convergence. Many of the same factors help drive biodiversity today, they noted. [1]

Cortés and Larsson propose calling the pattern a "Biotic Inflection": a period when many evolutionary lineages nearing extinction coexist with newly emerging groups that later diversify. [1]

At the same time, the authors conclude 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] They note that fossil assemblages rarely provide the sampling completeness, phylogenetic resolution, temporal control and environmental context needed to assess such properties in deep time.

Larsson said he thinks the team has found a new model of global biodiversity change, and that it remains to be seen how widespread it was and how its impacts can be quantified. Testing the proposal will require additional fossil sampling, more precise dating and comparisons with deposits elsewhere in the world.

## Sources

1. [Frontiers in Ecology and Evolution](https://doi.org/10.3389/fevo.2026.1848892)
2. [SciTechDaily](https://scitechdaily.com/120-million-years-ago-something-extraordinary-was-happening-in-earths-oceans)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-bf7ebc1343fd9bedc0466db8_mcgill_team_proposes/