New Study Reveals How Reptiles Divided the Spoils in Ancient Seas

Reconstruction of the Shonisaurus, a giant ichthyosaur. (Nobumichi Tamura.jpg)

(CN) — New research revealed Wednesday shows how ancient sea creatures and reptiles operated in Earth’s oceans millions of years ago.

While dinosaurs roamed and ruled Earth’s surface during the Mesozoic period roughly a hundred million years ago, underwater predators — such as sharks, giant lizards and the impressive and now extinct ichthyosaurs — dominated the ocean depths for generations in a complex ecosystem that researchers to this day are still trying to understand.

These efforts to unravel the many mysteries of how ancient sea reptiles thrived in Earth’s oceans were bolstered when a new study published in the journal Palaeontology announced that researchers from the University of Bristol successfully modeled the changing ecologies of these ancient creatures that shows how they swam and hunted in their prehistoric habitats.

According to the model constructed by scientists, these ancient reptiles could be divided into six ecological groups that defined how they lived and how they fed. 

The first three were different variations of predatorial groups, including pursuit predators that chased down their prey and two types of ambush predators, one that operated in shallow water and another in deep water, lurking in wait for potential prey to swim nearby. 

The other three included reptiles that could move on land as well as the water, a group of shallow-water shell-crushing and foraging reptiles and marine-based turtles that practiced a wide range of lifestyles.

Jane Reeves, a doctoral student at the University of Manchester and lead author of the study, said that while it is a challenge to figure out the roles and behavior of ancient creatures, the study’s decision to focus strictly on specific traits helped researchers uncover intriguing results.

“It’s difficult to work out the ecology and function of fossil animals but we decided to focus mainly on their feeding and swimming styles,” Reeves said with the release of the study. “I tracked down information on 371 of the best-known Mesozoic marine tetrapods, and coded each one for 35 ecological traits, including body size, diet, likely hunting style, tooth type, presence or absence of armor, limb shape and habitat.”

Researchers also found that a given sea reptile could change or travel through different types of ecological roles. The study specifically sought to explore an idea that the ichthyosaurs migrated through the ecospace during the lifetime of the species and found that the idea held water.

Researchers uncovered evidence that the ichthyosaurs changed from being a semi-terrestrial creature at the beginning of the Triassic era to an ambush hunter and finally a pursuit-hunting predator in the Jurassic and Cretaceous periods.

The study also notes that despite the size and strength of these prehistoric reptiles, most of them went out of their way to avoid direct competition with one another. 

Scientists point to creatures like the plesiosaurs that were hesitant to expand their underwater roles, seemingly content to operate in their own ecological lanes. This left a series of ecological niche roles unfilled until years later when new species of crocodiles and turtles emerged.

Reeves notes that animal behaviors can often be unpredictable, making research efforts like the one detailed in Wednesday’s study potentially vulnerable to uncertain or unproven ideas. 

But Reeves said she is confident that the data researchers collected greatly helped to shed meaningful light on the everyday lives of these ancient sea dwellers.

“You do have to be very careful in doing these kinds of studies, not to make any unfounded assumptions,” Reeves said. “We know animals can be opportunistic, and don’t always behave exactly how we think they should, but we’re confident that the data we collected reflects the most common, day-to-day, behaviors of each animal.

“These results give us a great insight into what was really happening under the surface of the Mesozoic seas.”

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