In the ancient ocean, monstrous creatures instilled fear in today's top predators. Who are they? (photo)

Today, the ocean covers more than half of the planet's surface and is home to an incredible number of species, including some of the most fearsome predators on Earth: orcas, sperm whales, and great white sharks. However, millions of years ago, in the ancient ocean, things were entirely different, and scientists believe that today's predators were not at the top of the food chain, as reported by Science Alert.

During the early Cretaceous period, around 130 million years ago, biodiversity thrived both on land and in the ocean. The water levels in ancient oceans were significantly higher, and they were home to monstrous predators unlike anything living today.

In a new study, a team from McGill University delved deep into an intriguing ecosystem from the early Cretaceous period, where marine reptiles the size of buses hunted other large carnivorous animals. The authors of the study believe they formed a rare seventh trophic level in their food chain.

It is important to note that modern oceans reach a maximum of the fifth or sixth trophic level, represented by apex predators. The trophic level indicates an organism's position in the food chain: the lower the level, the closer the animals are to the base of the chain. For instance, the first level consists of primary producers—algae and plants; the second level includes primary consumers, such as herbivores; the third level consists of predators that eat herbivores, while higher levels are reserved for predators that hunt other predators.

In their research, the scientists focused on studying the ancient inhabitants of the Paja Formation—a geological formation from the early Cretaceous period located in present-day Colombia. It is known that during that time, the ocean level was significantly higher, and much of this area was covered by a warm, shallow sea.

The authors of the study believe that during that time, the sea was likely teeming with life at all trophic levels, which was part of a broader surge in biodiversity during the Cretaceous period, driven by the breakup of the supercontinent Pangaea and a warm climate.

Supporting high-level apex predators requires a diverse, healthy ecosystem, and the dynamic nature of this prehistoric sea allowed some incredible leviathans to thrive. The Paja ecosystem is known to have been home to gigantic dolphin-like reptiles, such as ichthyosaurs, as well as crocodile-like creatures called teleosaurs, and long-necked pliosaurs, some of which reached lengths of over 10 meters.

The team notes that the potential for a seventh trophic level highlights how rich and complex the Paja ecosystem could have been around 130 million years ago. To shed light on this ancient habitat, the researchers reconstructed its ecological network by using a model of species interactions within the ecosystem. For this, the team utilized fossil remains of known animals previously found in the Paja Formation.

Key details, such as the body sizes of the animals and their dietary adaptations, were taken into account during the study. The scientists also drew on analogs from modern wildlife, which helped the team derive some unfossilized information.

It is noteworthy that this approach was previously mainly used to study modern ecosystems, but recently scientists have also applied it to fossils. The researchers drew inspiration from existing marine ecosystem networks based on contemporary ecosystems in the Caribbean and used this benchmark model to test and refine their Paja network.

Once the model was completed, it provided an unprecedented glimpse into one of the most vibrant marine networks known to science. According to co-author of the study, biologist at McGill University, Dirley Cortez, their work offers a broader understanding of ecology, both ancient and modern. Understanding this complexity helps us track how ecosystems evolve over time.