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Sept. 30 (UPI) -- While dinosaurs dominated dry land, a diversity of marine reptiles ruled ancient ocean ecosystems. Using a combination of modern ecological modeling techniques, researchers have for the first time detailed the ways ancient reptiles -- including crocodiles and giant lizards, as well as ichthyosaurs and plesiosaurs -- divvied up the spoils of the Mesozoic seas.
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According to the analysis, published Wednesday in the journal Paleonotology, the diversity of marine predators found in the Mesozoic seas were divided into six unique ecological categories based on how they lived, moved, hunted and ate.
"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," study author Jane Reeves, a doctoral student at the University of Manchester, said in a news release.
"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," said Reeves, who conducted the research while earning a masters degree in paleobiology at the University of Bristol.
Reeves and her colleagues showed one group of predators, called pursuit predators, preferred to chase their prey. Ambush predators, on the other hand, stayed hidden and ready to attack unsuspecting passersby -- some ambush predators preferred deep water, while others specialized in shallow water attacks.
Other reptiles that could still walk on land mostly foraged for mollusks and other shellfish in the shallows. Meanwhile, marine turtles adopted a variety of lifestyles.
"A problem with studies of form and function of fossils is that we have to be careful in reconstructing the behavior of ancient animals," said co-author Mike Benton.
"But in Jane's study, she used ecological characters from the start where their function had already been established. For example, sharp pointy teeth mean fish-eating, whereas broad, flat teeth mean shell crushing," said Benton, a professor of vertebrate paleontology at the University of Bristol who oversaw Reeves' research.
The new research also showed that different marine reptile groups evolved over time, diversifying across the different predator categories -- adapting to new ecoscapes as their physiology and hunting techniques changed.
"I'm especially interested in ichthyosaurs, and we wanted to test an idea that they had migrated through ecospace during the Mesozoic," said Bristol researcher Ben Moon, co-author and another co-supervisor of the research.
"Jane's study shows definite movement through time from being semi-terrestrial at the beginning of the Triassic to a wide range of ecologies, including ambush hunting, and finally pursuit predation in the Jurassic and Cretaceous," Moon said.
Researchers were also able to determine that for the most part the diversity of Mesozoic predators weren't directly competing with one another. At the end of the Triassic, following a series of marine reptile extinction events, surviving groups ichthyosaurs and plesiosaurs failed to take advantage of newly unoccupied ecological niches.
"Many niches were left empty until new groups of crocodiles and turtles emerged later in the Jurassic to take over these roles," said Bristol researcher Tom Stubbs, another co-supervisor.
Researchers suggest computation analysis of fossil assemblages can help scientists gain new insights into what ancient ecosystems actually looked like and how they functioned.
"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," Reeves said.
