Dinosaur ‘Menu’ Reveals How so Many Fearsome Predators Coexisted 100 Million Years Ago

Around 100 million years ago, large carnivorous dinosaurs and reptiles dominated the landscape in what we now call Africa. But how were so many fearsome predators able to exist side by side without outcompeting one another?

This is the question that a team of researchers from the Laboratory of Geology in Lyon, France, have tried to answer in a new study published in the journal Proceedings of the Royal Society B.

Using a new technique they developed themselves, the team examined fossilized remains from the time of the dinosaurs in order to reconstruct ancient food chains, enabling them to determine how so many predators could have coexisted.

Both sites—Gadoufaoua in Niger and the Kem Kem Beds in Morocco—contain fossils ranging in age from between 100 million and 120 million years old.

“In the ecosystems that we studied, predators are far more abundant than herbivorous dinosaurs, their most likely terrestrial preys,” palaeobiologist and geochemist Auguste Hassler, lead author of the study, told Newsweek.

The researchers measured the proportions of calcium isotopes—variants of calcium which differ in the number of neutrons—in the fossilized remains of tooth enamel and fish scales.

Because calcium in vertebrates is derived almost exclusively from food, the team was able to compare the proportion of calcium isotopes of potential prey, such as fish and herbivores, with that of carnivores to retrace the diets of these predators.

They found that in both locations, the carnivores had similar food preferences. For example, large carnivorous dinosaurs, like abelisaurids and carcharodontosaurids, liked to hunt land-dwelling herbivorous dinosaurs, while others, such as spinosaurids, preferred to eat fish.

Meanwhile, the diet of Sarchosuchus—which is not a dinosaur but a giant ancestor to modern crocodilians—consisted of a mixture of land and water-based prey.

Because of this, the researchers concluded that the different predators avoided competition by subtly sharing food resources.

thedinosaurm Teeth from the Gadoufaoua deposit (Niger). From left to right: teeth of a giant crocodile, Sarcosuchus imperator, a spinosaurid, a non-spinosaurid theropod (abelisaurid or carcharodontosaurid), a pterosaur, a hadrosaurid (a herbivorous dinosaur), a pycnodont (fish), and a small crocodylomorph. Auguste Hassler / LGL-TPE / CNRS-ENS de Lyon-Université Lyon 1

“All these predators were able to coexist in the same environments because they had different prey preferences,” Hassler said. “This prey partitioning is thus a key to understand their high abundance.”

The latest study provides rare evidence for the diet of dinosaurs, which are generally not well-studied. The scientists hope, however, their calcium isotope method could provide new avenues for research in this area because calcium is abundant and does not get altered through fossilization.