This giant was the 'heron from hell' – new research reveals controversial dinosaur secrets

Research by University of Chicago paleontologists and their partners reveals major flaws in previous theories suggesting that the giant sail-powered predator Spinosaurus actively hunted its prey underwater.

For years, there has been debate about how Cretaceous period– Age of sail-powered dinosaurs – Giant Egyptian Spinosaurus– He hunted his prey. Spinosaurus It was among the largest predators ever to roam the land and one of the most water-adapted animals, but was it an aquatic sea dweller, diving deep to chase its meals, or a semi-aquatic wader snatching its prey from the shallows close to shore?

A new analysis led by paleontologists from University of Chicago He re-examines his bone density as a way to determine his water habits.

Deep water swimmer or beach predator?

When providing a detailed description of an almost complete sample of Spinosaurus It was first published in Sciences In 2014, a University of Chicago-led research team described it as a devil that haunts the beach or swims on the surface, rather than a fully aquatic underwater predator (read more about the history Spinosaurus and its initial discovery). Later in 2020, an international group of researchers responded to this description with a study conducted in natureusing its newly discovered long tail bones to suggest that it propelled itself like an eel to hunt underwater.

A 2022 nature A study by several of these same authors confirmed their 2020 assessment making this clear Spinosaurus It had dense bones to use as ballast in diving like a penguin. They've also argued that there were some other spinosaurs, like its older African cousin SocumimusIts bones were less dense and it was likely that it was a wader.

Around the same time in 2022, a group of paleontologists at the University of Chicago collaborated with colleagues elsewhere to test these ideas by creating digital skeletons and flesh models of ancient organisms. Spinosaurus And Socumimus. Their results were published in eLifeI found that both Classify It will be unstable when swimming on the surface and far away Very thriving for diving And completely immersed.

the Spinosaurus The femur (left) was thinly sectioned with a diamond saw (middle) to reveal under magnification its bony structure (right). Credit: Stephanie Baumgart and Evan Saitta

Now, the same team has taken up the question of bone density, led by senior author Paul Serino, Ph.D., of the University of Chicago and first author Nathan Myhrvold, Ph.D., founder and CEO of Intellectual Ventures. Their study, “Diving Dinosaurs? Cautions on Using Bone Pressure and pFDA to Infer Lifestyle,” was recently published in the journal One plus.

“We've made thin sections of these species that have been used in bone density calculations, so we thought we'd start by trying to replicate their measurements,” said Serino, a professor of organismal biology and anatomy at the University of Chicago. Led the initial discovery of new Spinosaurus Sample in 2014. “But we encountered several factors that generated a range of values ​​sufficient to undermine the conclusions.”

New accounts of ancient fossils

The team began asking new questions about bone density, such as how to digitize thin sections, where to cut femur and rib bones, and whether to include bones from more than one individual.

Some modern aquatic mammals, such as manatees, have bulging, dense bones that help them stay underwater, like a diver's weight belt. Large land animals, such as elephants and dinosaurs, have dense bones to support increased body mass. Most modern birds and many including dinosaurs Spinosaurus They have the opposite condition, where there are air sacs attached to the lungs or inside the bones that act as a life jacket to prevent submersion. Assessing the water capabilities of extinct species e.g Spinosaurus You must take into account all these factors.

Given the complexity of understanding what bone density means, Sereno and his team worked with Myhrvold to re-evaluate how the statistical technique would be used in the 2022 tournament. nature The study was applied to support the claim that Spinosaurus He was a deep diver. This approach is similar to, known as flexible phylogenetic discriminant analysis (pFDA). Machine learning: pFDA trains a classification algorithm on a set of species whose lifestyle is well understood.

In principle, researchers could then use the algorithm to estimate the probability of the presence of poorly understood species e.g Spinosaurus It falls into one behavioral group or another. But in practice, Myhrvold said there are problems to overcome.

“Unfortunately, this technique only works properly if you have a lot of data, make comprehensive comparisons, and make sure the data meets certain statistical requirements,” he said. “None of these requirements were met in that previous study, so the results do not hold up under reexamination.”

The new paper should help paleontologists understand the dangers of pFDA and other types of broad statistical analyzes and how to avoid them. The researchers explain 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 results also show the importance of taking measurement errors and individual differences into account when assessing bone density.

“We believe Spinosaurus“It is one of the largest predators that ever evolved, and it needed additional bone strength to support its weight on its relatively short hind limbs,” Serino said. “Spinosaurus Able to wade into waterways more than six feet deep without floating, it can ambush fish of any size with its claws and jaws—but keep its toes firmly planted in the mud.

Reference: “Diving Dinosaurs? Cautions on Using Bone Compression and pFDA to Infer Lifestyle” by Nathan P. Myhrvold, Stephanie L. Baumgart, Daniel Vidal, Frank E. Fish, Donald M. Henderson, Evan T. Saitta, and Paul C. Sereno, March 6, 2024. , One plus.
doi: 10.1371/journal.pone.0298957

Additional authors on the study include Stephanie L. Baumgart of University of Florida; Daniel Vidal and Ivan T. Saitta of the University of Chicago; And Frank E. Fish of West Chester University in Pennsylvania; and Donald M. Henderson of the Royal Tyrrell Museum of Paleontology, Alberta, Canada.