Researchers at McGill University have reconstructed a 130-million-year-old marine ecosystem from Colombia, revealing predators that operated at a seventh trophic level, higher than any in modern oceans. This discovery highlights the intense complexity of ancient seas during the Cretaceous period. The findings underscore how competition drove the evolution of today's marine biodiversity.
Around 130 million years ago, during the Early Cretaceous period, the oceans teemed with life in ways that outstripped modern complexity. A study led by Dirley Cortés, a doctoral student in McGill University's Department of Biology, analyzed fossils from Colombia's Paja Formation to map an ancient food web. This geological site, formed amid rising sea levels and warmer global temperatures in the Mesozoic era, preserved evidence of enormous marine reptiles, including plesiosaurs and ichthyosaurs, some exceeding 10 meters in length, alongside diverse invertebrates.
Trophic levels, which indicate an organism's position in the food chain based on energy sources, typically max out at six in today's oceans, with top predators like killer whales and great white sharks. However, the Paja ecosystem supported creatures at a seventh level, demonstrating unparalleled ecological dominance. To build this network, the team used fossil body sizes, feeding traits, and analogies to modern Caribbean marine systems for validation.
"Our study is the first to examine these possible ecological interactions," Cortés said. "Understanding this complexity helps us trace how ecosystems evolve over time, shedding light on the structures that support today's biodiversity."
Co-author Hans Larsson, a professor in the Department of Biology, added, "These findings illuminate how marine ecosystems developed through intense trophic competition and shaped the diversity we see today."
Published in the Zoological Journal of the Linnean Society under the title "Top of the food chains: an ecological network of the marine Paja Formation biota from the Early Cretaceous of Colombia reveals the highest trophic levels ever estimated," the research was funded by the McGill-STRI Neotropical Environment Option and the Natural Sciences and Engineering Research Council of Canada. This work represents an initial foray into reconstructing full ancient food webs, with potential for broader comparisons as more fossil sites are studied.