Debunking the Myth: Was Spinosaurus Really a “7-Ton Heron From Hell?”

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. Credit: Daniel Navarro

Researchers think they have discovered critical flaws in the studies advocating for aquatic hunting behavior in Spinosaurus.

Nathan Myhrvold of Intellectual Ventures, US, and his team suggest in a study recently published in the open-access journal PLOS ONE, that the theory supporting the aquatic hunting behavior of Spinosaurus may have fundamental flaws.

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 the 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.

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

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.

Methodological Flaws and Recommendations

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 the 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.”

Reference: “Diving dinosaurs? Caveats on the use of bone compactness and pFDA for inferring lifestyle” 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.0298957