Roughly 130 million years ago, in an area within what is now central Columbia, the ocean was filled with a variety of species not seen today. Within that water swam several gigantic predators that make up the stuff of nightmares. These marine reptiles can reach lengths from 2 to 10 meters (about 6 to 32 feet), some with huge mouths full of teeth, others with relatively small heads (also full of teeth) attached to long, snake-like necks.
These giants share the ocean with countless smaller species, many of which are predators themselves. These included ichthyosaurs – dolphin-like reptiles – as well as turtles, fish, ammonites, crabs, molluscs, sharks and at least one type of crocodile.
Allowing all of these creatures to flourish must require an ecosystem to thrive at all levels. Thanks to discoveries in the so-called Baja Formation, a treasure trove where fossils are preserved abundantly and exquisitely, researchers are now beginning to learn how the ecosystem supports its many predators. And they may find hints of how it thrived so soon after the mass extinction that ended the Jurassic period.
Who ate what?
Derley Curtis is a Ph.D. candidate Redpath Museum from McGill University, a pre-doctoral fellow at the Smithsonian Tropical Research Institute, and a research fellow at Centro de Investigaciones Paleontológicas(CIP). She presented the data she and her team were working on from the Baja formation at the 2022 annual meeting of the Society of Vertebrate Paleontologists (SVP), which was held last November in Toronto.
The team’s goal is to dive deeper into the role each species played in the ancient oceans. In other words, from the apex predator to the smallest species in the sea, they hope to determine the ecological standing of each species. It’s mind-boggling, given the information gaps they have to overcome. Not all species are fossilized, for example, and a few fossils display the contents of their intestines to show what they ate. So how can scientists recreate an extinct ecosystem?
While acknowledging these limits to their study, the team compared each species’ size, aspects regarding their teeth, and other traits to analyze where they fell within this early Cretaceous food chain. Curtis explained, “This is a quantitative analysis. It is a starting point for developing energy flow models.”
“This food-food web was quantitatively reconstructed based on the inferred trophic interactions of marine producers, consumers and large predators,” she added.
Layers upon layers
One of the things they found was that there were more trophic levels, meaning longer food chains, in this ancient sea than there are in today’s oceans.
This, she explained, “means greater complexity in the ecosystem. As the levels increase, one can assume that there is more space for the linkages between species that occupy each of the trophic levels. The interesting question is whether higher levels mean greater stability in the system.” “What has been studied so far is that the base of marine systems has remained relatively stable for hundreds of millions of years. Studying the food web of Colombia’s Baja Formation can extend this discussion to even higher levels.”
A predatory reptile, a member of the pliosaurs.
This complexity stems in part from the diversity of predators within this ancient sea. Apex predators such as the pliosaur Monquirasaurus– a short-necked marine reptile that can reach a length of about 10 m (32 ft) – consists of a single trophic level. But a separate one consisted of smaller pliosaurs about 2 meters (6 feet) long such as Stenorhynchosaurus And Acostasure and ichthyosaurs. Sea turtles and elasmosaurs (long-necked reptiles) made up another component.
It’s tempting to assume that because of their size, pliosaurs might have fed on whatever swam between them, but there are still many unknowns regarding Pliosaur diet. Studies of their skulls indicated that they may not have had a bite force comparable to today’s crocodiles, a force that would have enabled them to grasp, roll and lunge their prey into submission. Stomach contents reveal a regular cephalopod diet, but some also include sharks, fish, turtles, ichthyosaurs, other marine reptiles, and even Leather dinosaur.
The remarkably long necks of elasmosaurus prompted the occurrence of many of them hypotheses about how they may have aided in predation. Could they have used their necks like today’s snakes: curling backwards, then striking prey? Could they have used them to help gather nutrients and food from the sea floor (benthic feeding)? Or do they simply swim with their necks fully extended, striking and ambushing the prey they pursue? These are also unanswered questions, but their teeth seem to indicate a fish diet.
An ecosystem in transition
“We were beginning to see that the Baja ecological network was very complex and diverse,” Curtis noted, adding that “the apex of the network was dominated by these predators feeding on large prey such as large fish and other relatively smaller marine reptiles, as well as ammonites.”
We don’t have ammonites in our oceans today; Nautilus may be the closest thing we have to some species of ammonite. Ammonites are ancient cephalopods that lived in thick shells, many of them tightly coiled. Found in fossil deposits all over the world. Some could be as small as a few centimeters, but others were about 3 meters (9 feet) across. Over 100 different species of ammonites have been found in the Baja Formation – ammonite fossils are so common that one species became regional code.
Curtis stated that “Materials from the Baja Formation provide useful insights for investigating the dynamics of Mesozoic marine systems, and ultimately how these systems responded to biotic and abiotic factors during the Early Cretaceous transition period.” That transition period marks the recovery from the environmental disasters and extinctions that marked it The end of the Jurassic period.
What is offered at SVP is just the beginning. A paper outlining their work is expected to be presented this year, and next steps include identifying “what the nutritional players are missing and, ultimately, generating energy flow models.”
She concluded, “The paleontological network theory is relatively new to paleontology. Perhaps one of the most challenging parts is that there are only a few Mesozoic sites to compare our data on a large scale. However, this research was exciting in terms of bringing new insights into evolution.” Mesozoic marine ecosystem and ecological networks”.
Gene Timmons (@employee) is a freelance writer with a strong passion for paleontology. Based in New Hampshire, she writes about paleontology (and some archaeology) on her blog mostmammoths.wordpress.com.
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