Spinosaurus Likely Spent Nearly All Its Time Underwater, Study Finds

Spinosaurus, the giant predator that lived in what is now northern Africa, probably spent the vast majority of its time submerged in water, according to a new study from Yale University. The work also suggests that some ancient marine reptiles long thought to be fully aquatic actually spent a lot of time on land, ScienceDaily reports.

The findings were published in the journal Current Biology. They add weight to one side of a long-running debate over how Spinosaurus lived.

How the researchers worked out where extinct animals lived

Paleontologists have long struggled with a basic question: did a given extinct animal live on land, in water, or both? Skeletons often send mixed signals, with some features pointing to swimming and others to movement and feeding on land.

To get around that, lead author Caleb Gordon built relatively simple machine learning models trained on living animals. The models learn the link between skeletal proportions and known lifestyles, then estimate how extinct species used aquatic habitats. They can also predict soft-tissue features, such as swimming structures, that rarely survive as fossils.

The team examined hundreds of fossil and modern specimens at the Yale Peabody Museum and dozens of other institutions. They collected more than 11,000 measurements, along with photographs and CT scans. They also used a statistical approach originally developed by naval forces during World War II. Gordon completed his doctorate at Yale earlier this year and is now a postdoctoral researcher at the Florida Museum of Natural History.

What the study says about Spinosaurus

Spinosaurus lived roughly 113 million to 94 million years ago. Scientists generally agree it was tied to watery environments, but not how it moved or hunted. One view pictures an animal that regularly dove and chased prey, like seals or penguins. Another sees something closer to a heron, wading along shorelines and in shallow water.

The Yale analysis supports the more aquatic view. Gordon said the models confidently recovered highly aquatic habits for the dinosaur, indicating that it spent the vast majority of its time submerged. The study does not settle every question about how Spinosaurus hunted, but it strengthens the case that the predator spent far more time in the water than out of it.

Marine reptiles that stayed tied to land

The researchers reached a different conclusion about mesosaurs, small marine reptiles that lived between 290 million and 274 million years ago in what are now parts of South Africa and eastern South America. According to the study, some ancient marine reptiles previously considered fully aquatic, as mesosaurs were, spent considerable time on land.

Why it matters

Dozens of major groups of mammals and reptiles returned to the water after their ancestors had moved onto land. Gordon noted that these groups evolved in strikingly similar ways, such as developing flippers and other swimming features, making them textbook examples of convergent evolution.

Senior author Bhart-Anjan Bhullar, an associate professor at Yale and associate curator at the Peabody Museum, said that reconstructing the lives of extinct animals rigorously, rather than just telling stories, is a precise and delicate task. The new method gives scientists a data-driven way to test such reconstructions, and to learn when and how these returns to the water happened.

Around Prague, based on reporting by ScienceDaily