Colombian Fossils Show Giant Sea Reptiles and Sharks Sharing an Ocean as Eras Shifted

Fossils from central Colombia show an ancient ocean where animal groups on the road to extinction lived alongside newer groups that were just beginning to thrive, according to a report from McGill University published by ScienceDaily. The researchers say the find suggests that major shifts in the history of life can happen without a mass extinction.

The team has given this pattern a name: a "Biotic Inflection." The work comes from McGill and the Centro de Investigaciones Paleontológicas (CIP) and appears in the journal Frontiers in Ecology and Evolution. The researchers stress that more evidence is needed before they can say how common such transitions were.

What did the researchers find in Colombia?

They studied fossils from the Paja Formation, an Early Cretaceous rock unit near Villa de Leyva, Colombia. According to the report, it preserves an unusual mix of surviving Jurassic lineages and emerging Cretaceous groups. Most of the fossils collected there are kept at the CIP.

Dirley Cortés, a PhD graduate at McGill, said the formation has yielded long-necked plesiosaurs, relatives of marine crocodiles, turtles, sharks and crustaceans. Together, he said, they make up the Paja Biota, which he described as one of the most ecologically complex marine communities found to date.

What is a “Biotic Inflection”?

Cortés and McGill biology professor Hans Larsson proposed the term for an evolutionary turning point. At such a point, older groups nearing extinction coexist with newer lineages that are starting to expand and diversify.

The idea is a contrast to the more familiar picture of a mass extinction clearing the way for new life. In a Biotic Inflection, the transition instead involves a period of unusually high diversity in which declining and rising groups share the same ecosystem.

Why was this ocean so diverse?

The researchers point to a combination of conditions. These include warm greenhouse temperatures, elevated sea levels and nutrient-rich coastal waters. They also cite new ocean connections between the eastern Pacific and the early Atlantic through what is now Colombia.

Larsson described this as a "perfect storm" of environmental factors known to promote ecological complexity. It coincided, he said, with ancient lineages that were about to disappear while new groups began to flourish. The report notes that many of these influences still shape biodiversity today.

In an earlier study, the same researchers reconstructed who ate whom in the Paja Biota. They found an intricate food web with an unusually large variety of apex predators at the top.

Why does it matter?

For general readers, this is a finding about how scientists read the deep past rather than something with direct everyday consequences. If the concept holds up, it would add a second route to major biological change alongside mass extinctions: a period of coexistence and high diversity.

Larsson said he believes the team has found a new model of global biodiversity change. He added that researchers must now work out how widespread it was and how to measure its effects.

How certain is the idea?

It is a proposal based on one fossil formation, and the authors say it is not yet established as a general pattern. According to the report, answering that question will require additional fossil discoveries, more accurate estimates of fossil ages, and comparisons with geological formations elsewhere in the world.

The research was funded by several sources, including the Natural Sciences and Engineering Research Council of Canada, the Smithsonian Tropical Research Institute, the Anders Foundation and the 1923 Fund.

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Around Prague, based on reporting by ScienceDaily