Doing what they do higher than any animal that ever developed, a pair of the large sail-backed predators, Spinosaurus aegyptiacus, wade into nearshore waters for prey as pterosaurs soar overhead some 95 million years in the past on the northern coast of Africa. Credit score: Daniel NavarroResearch carried out by UChicago paleontologists and their companions reveals important flaws in earlier theories suggesting that the sail-backed large predator Spinosaurus actively hunted its prey underwater.For years, controversy has swirled round how a Cretaceous-era, sail-backed dinosaur—the large Spinosaurus aegyptiacus—hunted its prey. Spinosaurus was among the many largest predators ever to prowl the Earth and one of the crucial tailored to water, however 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 near shore?A brand new evaluation led by paleontologists from the College of Chicago reexamines the density of its bones as a means of figuring out its life habits in water.Deep water swimmer or shoreline predator?When detailed descriptions of an almost full specimen of Spinosaurus have been first printed in Science in 2014, a UChicago-led analysis workforce pitched it as a shoreline stalking or floor swimming demon, not a completely aquatic underwater predator (learn extra concerning the historical past of Spinosaurus and its preliminary discovery). Later in 2020, a global group of researchers countered that description with a examine in Nature, utilizing its newly found, tall-spined tail bones to recommend that it propelled itself like an eel to hunt underwater.A 2022 Nature examine by lots of those self same authors confirmed their 2020 evaluation displaying that Spinosaurus had dense bones to make use of as ballast in diving like a penguin. In addition they argued that another spinosaurids, comparable to its older African cousin Suchomimus, had much less dense bones and have been seemingly waders.About the identical time in 2022, a bunch of paleontologists at UChicago teamed up with colleagues elsewhere to check these concepts by creating digital skeletons and flesh fashions of the Spinosaurus and Suchomimus. Their outcomes, printed in eLife, discovered that each species would have been unstable when swimming on the floor and much too buoyant to dive and totally submerge.The Spinosaurus thigh bone (left) was skinny sectioned with a diamond noticed (center) to disclose beneath magnification its bone construction (proper). Credit score: Stephanie Baumgart and Evan SaittaNow that very same workforce has taken on the query of bone density, led by senior writer Paul Sereno, PhD, from UChicago and first writer Nathan Myhrvold, PhD, Founder and CEO of Mental Ventures. Their examine, “Diving dinosaurs? Caveats on the usage of bone compactness and pFDA for inferring life-style,” was just lately printed within the journal PLOS ONE.“We had made the skinny sections of those species that have been used for bone density calculations, and so we thought we might begin by making an attempt to copy their measurements,” stated Sereno, who’s a Professor of Organismal Biology and Anatomy at UChicago and co-led the preliminary discovery of the brand new Spinosaurus specimen in 2014. “However we encountered many elements that generated a variety of values—sufficient to undermine the conclusions.”New calculations for historic fossilsThe workforce started by asking new questions on bone density, comparable to find out how to digitize skinny sections, the place to slice via the thigh and rib bones, and whether or not to incorporate bones from a couple of particular person.Some trendy aquatic mammals like manatees have swollen, dense bones to assist them keep underwater, like a scuba diver’s weight belt. Massive land animals, like elephants and dinosaurs, even have dense bones to help their elevated physique mass. Most trendy birds and lots of dinosaurs together with Spinosaurus have the other situation, with air sacs connected to lungs or inside bones that act like a life vest stopping submergence. Assessing the aquatic talents of an extinct species like Spinosaurus must take account of all these elements.Given the complexity of understanding the which means of bone density, Sereno and workforce labored with Myhrvold to reevaluate how the statistical approach used within the 2022 Nature examine was utilized to help the declare that Spinosaurus was a deep diver. The strategy, generally known as phylogenetic versatile discriminant evaluation (pFDA), is like machine studying: the pFDA approach trains a classification algorithm on a bunch of species whose life-style is properly understood.In precept, researchers may then use the algorithm to estimate the chance {that a} poorly understood species comparable to Spinosaurus falls into one behavioral group or one other. In observe, nonetheless, Myhrvold stated there are issues that have to be overcome.“Sadly, that approach doesn’t work correctly until you will have numerous information, you make apples-to-apples comparisons, and also you verify that the information meet sure statistical stipulations,” he stated. “None of these necessities have been met in that earlier examine, so the outcomes simply didn’t maintain up beneath reexamination.”The brand new paper ought to assist paleontologists perceive the pitfalls of pFDA and other forms of broad statistical analyses and find out how to keep away from them. The researchers present that it is very important use constant and goal standards to determine which species to incorporate and exclude, in addition to find out how to classify their conduct. The findings additionally show the significance of taking measurement errors and particular person variations under consideration when assessing bone density.“We expect Spinosaurus, one of many largest predatory animals ever to have developed, wanted further bone energy to help its weight on its comparatively quick hind limbs,” Sereno stated. “Spinosaurus was capable of wade into waterways greater than six toes deep with out floating, the place it may ambush fish of any dimension with its claws and jaws—however all whereas maintaining its toes firmly anchored within the mud.”Reference: “Diving dinosaurs? Caveats on the usage of bone compactness and pFDA for inferring life-style” by Nathan P. Myhrvold, Stephanie L. Baumgart, Daniel Vidal, Frank E. Fish, Donald M. Henderson, Evan T. Saitta and Paul C. Sereno, 6 March 2024, PLOS ONE.DOI: 10.1371/journal.pone.0298957Additional authors on the examine embrace Stephanie L. Baumgart from the College of Florida; Daniel Vidal and Evan T. Saitta from UChicago; Frank E. Fish from West Chester College in Pennsylvania; and Donald M. Henderson from the Royal Tyrrell Museum of Paleontology, Alberta, Canada.