For years, controversy has swirled around how a Cretaceous-era, sail-backed dinosaur—the giant Spinosaurus aegyptiacus—hunted its prey. Spinosaurus was among the largest predators ever to prowl the Earth and one of the most adapted to water, but was it an aquatic denizen of the seas, diving deep to chase down its meals, or a semiaquatic wader that snatched prey from the shallows close to shore?
Dueling studies, each led by paleontologists from the University of Chicago, contribute new entries to this ongoing debate by reexamining the density of Spinosaurus bones.
Deep water swimmer or shoreline predator?
When detailed descriptions of a nearly complete specimen of Spinosaurus were first published in Science in 2014, a UChicago research team, co-led by Paul Sereno, PhD, Professor of Organismal Biology and Anatomy, pitched it as the first truly semiaquatic dinosaur, with muscular hind legs and webbed feet used for paddling and a flexible, undulating tail (read more about the history of Spinosaurus and its initial discovery).
Later in 2020, an international group of researchers countered that description with a study in Nature, using its newly discovered, tall-spinedtail bones to further support the theory that it propelled itself like an eel to hunt underwater.
A 2022 Nature study by many of those same researchers, including lead author Matteo Fabbri, PhD, who is currently a Chicago Fellows postdoctoral scholar at UChicago, backed their 2020 assessment showing that Spinosaurus also had dense bones to use as ballast for diving like a penguin. They also argued that some other spinosaurids, such as its older African cousin Suchomimus, had less dense bones and were likely waders.
About the same time in 2022, Sereno again teamed up with colleagues elsewhere to test these ideas by creating digital skeletons and flesh models of the Spinosaurus and Suchomimus. Their results, published in eLife, claimed that both species would have been unstable when swimming at the surface and far too buoyant to dive and fully submerge.
Now Sereno and that same team, including lead author Nathan Myhrvold, PhD, Founder and CEO of Intellectual Ventures, has also taken on the question of bone density. Their study, “Diving dinosaurs? Caveats on the use of bone compactness and pFDA for inferring lifestyle,” appeared on March 6, 2024, in the journal PLOS ONE.
“We had made the thin sections of these species that were used for [Fabbri’s] bone density calculations, and so we thought we would start by trying to replicate their measurements,” Sereno said. He argues that his team’s new calculations confirm that Spinosaurus wasn’t well-suited to dive deep and hunt underwater.