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In a stunning display of natural predator behavior in the primeval world, a pair of the sail-backed creatures – the gargantuan Spinosaurus aegyptiacus – are depicted in pursuit of prey in the crepuscular waters, while pterosaurs daintily crisscross the sky overhead. This scene harks back to approximately 95 million years ago on the northern coast of Africa. Credit: Daniel Navarro
Rigorous scientific inquiry unveiled by a team of indefatigable paleontologists from UChicago alongside their distinguished partners punctures significant holes in erstwhile theories that professed the sail-backed colossal predator – the Spinosaurus, indulged in active underwater hunting.
The gargantuan sail-backed creature of the Cretaceous epoch – the Spinosaurus aegyptiacus – has been a subject of intense intellectual debate surrounding its hunting techniques for a considerable length of time. Spinosaurus, one of the most formidable predators to stride the terrestrial surface, showcased distinctive aquatic adaptations. But the question that has vexed scientists pertains to its aquatic lifestyle. Was it a deep-sea diver, torpedoing to apprehend its prey, or a shoreline lurker, snapping up unsuspecting victims from the shallows?
Meta-analysis steered by UChicago paleontologists scrutinizes the bone density of this magnificent creature as an indication of its aquatic habits.
An amphibious predator or a deep-sea hunter?
When Science initially published detailed descriptions of an almost complete specimen of Spinosaurus in 2014, a group of researchers led by UChicago proposed it as an aquatic ambush predator, rather than a fully-submerged hunter. Contrarily, in 2020, an international assembly of scholars propounded that the dinosaur propelled itself similar to an eel to catch underwater prey, a theory deduced from its newly discovered, tall-spinous tail bones.
A 2022 Nature study by similar collaborators as before gave further credibility to their earlier conjecture, asserting that Spinosaurus had compact bones that facilitated it to dive like a penguin by acting as a balancer. This study also brought to light that its African antecedent, Suchomimus, owing to less dense bones, was more likely a wading creature.
Simultaneously, a research team at UChicago, collaborating with global peers, put these theories to test. They utilized digital technology to construct skeletal and flesh models of the Spinosaurus and Suchomimus. Their findings, revealed in eLife, concluded that both these creatures would have been unstable while swimming up-top and too buoyant to dive completely into the water.
The indomitable team sought to further delve into the mystery surrounding bone density, a pursuit spearheaded by senior author, Paul Sereno, PhD, from UChicago and first author Nathan Myhrvold, PhD, Founder, and CEO of Intellectual Ventures. Their findings, chronicled in an enlightening paper titled “Diving dinosaurs? Caveats on the use of bone compactness and pFDA for inferring lifestyle,” recently graced the reputed journal PLOS ONE.
“Our aim was to recreate the measurements used in previous studies for bone density calculations. However, we ran into numerous variables that projected a vast spectrum of values- rendering initial conclusions questionable,” said Sereno, who is also a Professor of Organismal Biology and Anatomy at UChicago and had the privilege to lead the inaugural discovery of the new Spinosaurus specimen in 2014. “Spinosaurus, one of the largest carnivorous animals ever to have evolved, probably required extra bone density to support its weight on its relatively short hind limbs. It was perfectly capable of wading in deep water to engage in ambush hunting, managing to keep its extraordinary balance using its toes anchored firmly in the mud.”
Through continued study, paleontologists should better comprehend the potential pitfalls associated with this field of analysis. This collaborative research underscores the importance of meticulous and consistent criteria when deciding which species to include, and exclude from studies, as well as classifications of behaviour. They should also accommodate measurement errors and variations among individual species during the investigation of bone density.
