Giant dinosaur was “heron from hell,” not a deep diver, says new analysis
Study by UChicago paleontologists and colleagues uncovers major issues with earlier suggestions that the sail-backed mega-predator Spinosaurus pursued prey underwater.
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DOING WHAT THEY DO BETTER THAN ANY ANIMAL THAT EVER EVOLVED, A PAIR OF THE GIANT SAIL-BACKED PREDATORS, SPINOSAURUS AEGYPTIACUS, WADE INTO NEARSHORE WATERS FOR PREY AS PTEROSAURS SOAR OVERHEAD SOME 95 MILLION YEARS AGO ON THE NORTHERN COAST OF AFRICA.
view moreCREDIT: DANIEL NAVARRO
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?
A new analysis led by paleontologists from the University of Chicago reexamines the density of its bones as a way of determining its life habits in water.
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-led research team pitched it as a shoreline stalking or surface swimming demon, not a fully aquatic underwater predator (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-spined tail bones to suggest that it propelled itself like an eel to hunt underwater.
A 2022 Nature study by many of those same authors confirmed their 2020 assessment showing that Spinosaurus had dense bones to use as ballast in 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, a group of paleontologists at UChicago 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, found that both species would have been unstable when swimming at the surface and far too buoyant to dive and fully submerge.
Now that same team has taken on the question of bone density, led by senior author Paul Sereno, PhD, from UChicago and first author Nathan Myhrvold, PhD, Founder and CEO of Intellectual Ventures. Their study, “Diving dinosaurs? Caveats on the use of bone compactness and pFDA for inferring lifestyle,” appeared in the journal PLOS ONE.
“We had made the thin sections of these species that were used for bone density calculations, and so we thought we would start by trying to replicate their measurements,” said Sereno, who is a Professor of Organismal Biology and Anatomy at UChicago and co-led the initial discovery of the new Spinosaurus specimen in 2014. “But we encountered many factors that generated a range of values—enough to undermine the conclusions.”
New calculations for ancient fossils
The team began by asking new questions about bone density, such as how to digitize thin sections, where to slice through the thigh and rib bones, and whether to include bones from more than one individual.
Some modern aquatic mammals like manatees have swollen, dense bones to help them stay underwater, like a scuba diver’s weight belt. Large land animals, like elephants and dinosaurs, also have dense bones to support their increased body mass. Most modern birds and many dinosaurs including Spinosaurus have the opposite condition, with air sacs attached to lungs or inside bones that act like a life vest preventing submergence. Assessing the aquatic abilities of an extinct species like Spinosaurus needs to take account of all these factors.
Given the complexity of understanding the meaning of bone density, Sereno and team worked with Myhrvold to reevaluate how the statistical technique used in the 2022 Nature study was applied to support the claim that Spinosaurus was a deep diver. The approach, known as phylogenetic flexible discriminant analysis (pFDA), is like machine-learning: the pFDA technique trains a classification algorithm on a group of species whose lifestyle is well understood.
In principle, researchers could then use the algorithm to estimate the likelihood that a poorly understood species such as Spinosaurus falls into one behavioral group or another. In practice, however, Myhrvold said there are problems that must be overcome.
“Unfortunately, that technique does not work properly unless you have lots of data, you make apples-to-apples comparisons, and you check that the data meet certain statistical prerequisites,” he said. “None of those requirements were met in that earlier study, so the results just didn’t hold up under reexamination.”
The new paper should help paleontologists understand the pitfalls of pFDA and other kinds of broad statistical analyses and how to avoid them. The researchers show that it is important to use consistent and objective criteria to decide which species to include and exclude, as well as how to classify their behavior. The findings also demonstrate the importance of taking measurement errors and individual variations into account when assessing bone density.
“We think Spinosaurus, one of the largest predatory animals ever to have evolved, needed extra bone strength to support its weight on its relatively short hind limbs,” Sereno said. “Spinosaurus was able to wade into waterways more than six feet deep without floating, where it could ambush fish of any size with its claws and jaws—but all while keeping its toes firmly anchored in the mud.”
Additional authors on the study include Stephanie L. Baumgart from the University of Florida; Daniel Vidal and Evan T. Saitta from UChicago; Frank E. Fish from West Chester University in Pennsylvania; and Donald M. Henderson from the Royal Tyrrell Museum of Paleontology, Alberta, Canada.
The Spinosaurus thigh bone (left) was thin sectioned with a diamond saw (middle) to reveal under magnification its bone structure (right).
CREDIT
Stephanie Baumgart and Evan Saitta
JOURNAL
PLoS ONE
METHOD OF RESEARCH
Computational simulation/modeling
SUBJECT OF RESEARCH
Animal tissue samples
ARTICLE TITLE
Diving dinosaurs? Caveats on the use of bone compactness and pFDA for inferring lifestyle
ARTICLE PUBLICATION DATE
6-Mar-2024
Diving dinosaurs? Certain methods may be unsuitable for inferring dino lifestyles
Researchers believe they have found critical flaws in research supporting aquatic pursuit hunting in Spinosaurus
Peer-Reviewed PublicationIMAGE:
OING WHAT THEY DO BETTER THAN ANY ANIMAL THAT EVER EVOLVED, A PAIR OF THE GIANT SAIL-BACKED PREDATORS, SPINOSAURUS AEGYPTIACUS, WADE INTO NEARSHORE WATERS FOR PREY AS PTEROSAURS SOAR OVERHEAD SOME 95 MILLION YEARS AGO ON THE NORTHERN COAST OF AFRICA. PAINTING BY DANIEL NAVARRO.
view moreCREDIT: DANIEL NAVARRO, CC-BY 4.0 (HTTPS://CREATIVECOMMONS.ORG/LICENSES/BY/4.0/)
The support for the hypothesis of Spinosaurus as an aquatic pursuit predator may have had fundamental flaws, according to Nathan Myhrvold of Intellectual Ventures, US and colleagues, in a study published March 6, 2024 in the open-access journal PLOS ONE.
Paleontologists generally agree that the famous Spinosaurus was a fish-eater, but exactly how these dinosaurs caught their prey is the subject of lively debate, with some researchers suggesting that they hunted on the shore, some that they waded or swam in the shallows, and others that they were aquatic pursuit predators. One recent study provided support for the latter hypothesis using a fairly new statistical method called phylogenetic flexible discriminant analysis (pFDA) to analyze density and proportions of spinosaur bones. In the present study, Myhrvold and colleagues critically assess the methods of that prior research and identify significant flaws.
This assessment identifies inconsistencies and biases in the former study’s selection of data, as well as in the definitions of certain behavioral terms. The researchers also find that this method has low accuracy when applied to the datasets used in that study due to small sample sizes and high variability of certain data. Myhrvold and colleagues believe that there are enough problems with this methodology to invalidate the findings of the previous research.
This new study does not aim to settle the debate over the lifestyle of spinosaurid dinosaurs, but it does refute the conclusions of the previous paper which supported the aquatic pursuit predator hypothesis, an idea which the authors note is also contradicted by several other studies. The authors also provide guidelines for future research, urging caution when applying pFDA to limited datasets, and highlighting limitations in the use of bone density to infer aquatic lifestyles in dinosaurs.
The authors add: “Spinosaurus, and its close relatives, are fascinating because of their unusual anatomical features, the scarcity of specimens, and the fact that scientists had not found bones from parts of its body until very recently (2020). Unlike other meat eating dinosaurs, there are strong clues that it lived near water and ate fish or other aquatic fare. This has fueled a lot of controversy about how Spinosaurus lived—was it a fast swimming predator that chased fish like a sea lion? Or was it an ambush predator at the water’s edge, grasping with its clawed hands like a giant version of a brown bear chasing salmon, or plunging its head into water like a 7-ton heron from hell? Fabbri et al. attempted to resolve the lifestyle question using statistics of bone density, but we found that the statistical method and data used are inaccurate and inappropriate.”
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In your coverage please use this URL to provide access to the freely available article in PLOS ONE: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0298957
Citation: Myhrvold NP, Baumgart SL, Vidal D, Fish FE, Henderson DM, Saitta ET, et al. (2024) Diving dinosaurs? Caveats on the use of bone compactness and pFDA for inferring lifestyle. PLoS ONE 19(3): e0298957. https://doi.org/10.1371/journal.pone.0298957
Author Countries: USA, Spain, Canada
Funding: The author(s) received no specific funding for this work.
JOURNAL
PLoS ONE
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Diving dinosaurs? Caveats on the use of bone compactness and pFDA for inferring lifestyle
ARTICLE PUBLICATION DATE
6-Mar-2024
COI STATEMENT
The authors have declared that no competing interests exist.
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