The Paja Formation: An ecosystem of monsters

Roughly 130 million years ago, in an area within what is now central Colombia, the ocean was filled with a diversity of species unseen today. Within that water swam several massive apex predators that are the stuff of nightmares. These marine reptiles could reach lengths of 2 to 10 meters (about 6 to 32 feet), some with enormous mouths filled with teeth, others with relatively small heads (also filled with teeth) attached to long, snake-like necks.

These giants shared the ocean with countless smaller species, many of them predators themselves. These included ichthyosaurs—dolphin-like reptiles—as well as turtles, fish, ammonites, crabs, mollusks, sharks, and at least one species of crocodyliform.

Allowing all these creatures to thrive must have required a flourishing ecosystem at all levels. Thanks to discoveries in what's called the Paja Formation, a treasure trove where fossils are abundantly and exquisitely preserved, researchers are now beginning to figure out how the ecosystem supported so many apex predators. And they may find hints of how it flourished so soon after a mass extinction brought the Jurassic to a close.

Who ate what?

Dirley Cortés is a PhD candidate at the Redpath Museum of McGill University, a predoctoral fellow at the Smithsonian Tropical Research Institute, and a researcher at the Centro de Investigaciones Paleontológicas(CIP). She presented data she and her team have been working on from the Paja Formation at the 2022 annual meeting of the Society of Vertebrate Paleontologists (SVP), held this past November in Toronto.

The team's goal is to dive much deeper into the role each species played in ancient oceans. In other words, from apex predator to the tiniest species within the sea, they hope to determine each species' ecological niche. It's mind-boggling, given the gaps of information they have to overcome. Not all species fossilize, for example, and few fossils offer gut contents to show what they ate. So how can scientists recreate an extinct ecosystem?

Acknowledging these limits of their study, the team compared the size of each species, aspects about their respective teeth, and other attributes to analyze where they fell within this early Cretaceous food chain. "This," Cortés explained, "is a quantitative analysis. It is a starting point to develop energy flow models."

"This trophic food web is quantitatively reconstructed based on inferred trophic interactions of marine producers, consumers, and large-apex-predators," she added.