For a long time, non-avian dinosaurs (the dinos that didnt branch off into birds) were the only group that didnt have any water-dwellers. That changed in 2014, when a brand-new Spinosaurus skeleton was explained by Nizar Ibrahim at the University of Portsmouth.
Lead author Matteo Fabbri doing fieldwork. Credit: Diego Mattarelli
Scientists already knew that spinosaurids invested a long time by water– their long, cone-shaped teeth and croc-like jaws are comparable to other water predators, and some fossils had actually been found with tummies filled with fish. But the brand-new Spinosaurus specimen explained in 2014 had actually pulled back nostrils, brief hind legs, paddle-like feet, and a fin-like tail: all signs that pointed to a water lifestyle. But scientists have continued to debate whether spinosaurids really swam for their food or if they simply stood in the shallows and dipped their heads in to purchase victim. This continued back-and-forth led Fabbri and his colleagues to look for another way to resolve the problem.
” The concept for our research study was, okay, plainly we can translate the fossil data in various ways. One of these laws concerns density and the capability of immersing into water.”
Simone Maganuco (middle), Davide Bonadonna (ideal) and lead author Matteo Fabbri (left) organizing fossils at night. Credit: Nanni Fontana
Across the animal kingdom, bone density is an inform in regards to whether that animal is able to sink below the surface area and swim. “Previous studies have actually shown that mammals adapted to water have dense, compact bone in their postcranial skeletons,” says Fabbri. Thick bone works as buoyancy control and enables the animal to immerse itself.
” We believed, okay, maybe this is the proxy we can utilize to determine if spinosaurids were really aquatic,” states Fabbri.
Fabbri and his associates, including co-corresponding authors Guillermo Navalón at Cambridge University and Roger Benson at Oxford University, put together a dataset of thigh and rib bone cross-sections from 250 types of living and extinct animals, both water-dwellers and land-dwellers. The researchers compared these cross-sections to cross-sections of bone from Spinosaurus and its relatives Baryonyx and Suchomimus. “We had to divide this research study into successive actions,” says Fabbri. “The very first one was to comprehend if there is really a universal correlation in between bone density and ecology. And the 2nd one was to presume ecological adaptations in extinct taxa” Essentially, the group had to show a proof of concept among animals that are still alive that we know for sure are marine or not, and then used them to extinct animals that we cant observe.
Figure from paper revealing relationship in between bone density and ecology. Credit: Fabbri et al
. When picking animals to include in the study, the researchers cast a broad web. “We were trying to find severe diversity,” states Fabbri. “We included seals, whales, elephants, mice, hummingbirds. We have dinosaurs of different sizes, extinct marine reptiles like mosasaurs and plesiosaurs. We have animals that weigh numerous lots, and animals that are simply a few grams. The spread is huge.”.
This menagerie of animals exposed a clear link in between bone density and marine foraging habits: animals that immerse themselves underwater to discover food have bones that are almost entirely solid throughout, whereas cross-sections of land-dwellers bones look more like donuts, with hollow. “There is a very strong correlation, and the best explanatory model that we found remained in the correlation between bone density and sub-aqueous foraging. This indicates that all the animals that have the habits where they are fully submerged have these dense bones, and that was the excellent news,” says Fabbri.
Figure from paper comparing animals bone densities. Credit: Fabbri et al
. When the researchers used spinosaurid dinosaur bones to this paradigm, they discovered that Spinosaurus and Baryonyx both had the sort of thick bone related to complete submersion. The closely related Suchomimus had hollower bones. It still lived by water and consumed fish, as evidenced by its crocodile-mimic snout and cone-shaped teeth, but based upon its bone density, it wasnt in fact swimming.
Other dinosaurs, like the giant long-necked sauropods likewise had dense bones, but the researchers do not think that indicated they were swimming. “Very heavy animals like elephants and rhinos, and like the sauropod dinosaurs, have really dense limb bones, because theres a lot tension on the limbs,” discusses Fabbri. “That being said, the other bones are quite light-weight. Thats why it was very important for us to look at a variety of bones from each of the animals in the study.” And while there are restrictions to this type of analysis, Fabbri is excited by the capacity for this study to tell us about how dinosaurs lived.
” One of the huge surprises from this study was how rare undersea foraging was for dinosaurs, and that even amongst spinosaurids, their behavior was far more varied that we d believed,” says Fabbri.
Jingmai OConnor, a manager at the Field Museum and co-author of this study, says that collective studies like this one that draw from numerous specimens, are “the future of paleontology. Theyre extremely lengthy to do, but they let scientists shed light onto huge patterns, instead of making qualitative observations based on one fossil. Its really awesome that Matteo had the ability to pull this together, and it needs a lot of perseverance.”.
Fabbri likewise keeps in mind that the study demonstrates how much details can be gleaned from incomplete specimens. “The good news with this research study is that now we can move on from the paradigm where you need to referred to as much as you can about the anatomy of a dinosaur to understand about its ecology, because we reveal that there are other trusted proxies that you can use. If you have a new species of dinosaur and you just have just a few bones of it, you can develop a dataset to compute bone density, and at least you can presume if it was marine or not.”.
Reference: “Subaqueous foraging amongst carnivorous dinosaurs” by Matteo Fabbri, Guillermo Navalón, Roger B. J. Benson, Diego Pol, Jingmai OConnor, Bhart-Anjan S. Bhullar, Gregory M. Erickson, Mark A. Norell, Andrew Orkney, Matthew C. Lamanna, Samir Zouhri, Justine Becker, Amanda Emke, Cristiano Dal Sasso, Gabriele Bindellini, Simone Maganuco, Marco Auditore and Nizar Ibrahim, 23 March 2022, Nature.DOI: 10.1038/ s41586-022-04528-0.
By evaluating the density of spinosaurid bones and comparing them to other animals like alligators, hippos, and penguins, the team discovered that Spinosaurus and its close relative Baryonyx had dense bones that likely would have allowed them to submerge themselves undersea to hunt. Throughout the animal kingdom, bone density is a tell in terms of whether that animal is able to sink beneath the surface and swim. This menagerie of animals exposed a clear link in between bone density and marine foraging behavior: animals that immerse themselves undersea to discover food have bones that are practically completely strong throughout, whereas cross-sections of land-dwellers bones look more like donuts, with hollow. When the researchers used spinosaurid dinosaur bones to this paradigm, they found that Spinosaurus and Baryonyx both had the sort of thick bone associated with full submersion. If you have a brand-new types of dinosaur and you just have only a couple of bones of it, you can create a dataset to determine bone density, and at least you can presume if it was aquatic or not.”.
Contrary to previous tips, this animal was not a heron-like wader– it was a “river monster,” actively pursuing victim in a huge river system located in modern-day North Africa. Thick bones in the skeleton of Spinosaurus strongly suggest it spent a significant amount of time immersed in the water.
Its close cousin Baryonyx most likely swam too, however Suchomimus mayve waded like a heron.
By analyzing the density of spinosaurid bones and comparing them to other animals like hippos, penguins, and alligators, the group discovered that Spinosaurus and its close relative Baryonyx had dense bones that likely would have allowed them to immerse themselves underwater to hunt. Another related dinosaur called Suchomimus had lighter bones that would have made swimming more tough, so it likely waded rather or invested more time on land like other dinosaurs.
Baryonyx, from Surrey in England, swims through an ancient river with a fish in its jaws. Like its much bigger African relative Spinosaurus, Baryonyx had thick bones, suggesting that it too invested much of its time submerged in water.
” The fossil record is difficult– amongst spinosaurids, there are only a handful of partial skeletons, and we dont have any complete skeletons for these dinosaurs,” says Matteo Fabbri, a postdoctoral researcher at the Field Museum and the lead author of the study in Nature. “Other research studies have actually focused on interpretation of anatomy, however clearly if there are such opposite interpretations relating to the same bones, this is already a clear signal that possibly those are not the very best proxies for us to infer the ecology of extinct animals.”
