This is the conclusion of an international team of paleontologists who present their results in the journal Nature and who have analyzed and compared the densities of 380 bones from a wide range of current and extinct animals.
After being declared the first known swimming dinosaur in 2020, Spinosaurus was, at more than 18 meters long, the largest predatory dinosaur that ever lived. Now, a new analysis of its remains has pointed the needle towards the concept that it dived underwater to hunt its prey; that he was an excellent swimmer and that he took advantage of this advantage to hunt underwater.
Discovering Spinosaurus Behavior
Researchers at the Field Museum in Chicago (USA) came to this conclusion after studying the bone density of spinosaurids and comparing them to other animals such as penguins, hippos and alligators. They found that while Spinosaurus and its close relative Baryonyx had dense bones that allowed them to dive into water, another related dinosaur called Suchomimus had much lighter bones that would have made swimming difficult.
The experts assembled a dataset of femur and rib cross-sections from 250 species of living and extinct animals, both terrestrial and aquatic. This selection of animals revealed a clear link between bone density and aquatic foraging behavior : those that dive underwater to find food have bones that are almost completely solid, while cross-sections of the bones of terrestrial animals resemble each other. more like doughnuts, with holes in the center.
“The fossil record is complicated: Among spinosaurids, there are only a handful of partial skeletons, and we don’t have complete skeletons for these dinosaurs,” says Matteo Fabbri, a postdoctoral researcher at the Field Museum and lead author of the study. “Other studies have focused on the interpretation of the anatomy, but clearly if there are such opposite interpretations regarding the same bones, this is already a clear signal that perhaps those are not the best indicators to infer the ecology of the animals. extinct”.
Life began in the water
Life came from water, so it is common to find that most land vertebrates have limbs that returned to the water . For example, of mammals, otters, tapirs or hippopotamuses, they are semi-aquatic; in birds, cormorants and penguins are also; in reptiles, crocodiles, sea snakes or alligators.
So it was an aquatic animal?
The study suggests yes. For aquatic hunters to dive into the water, they need dense and compact bones, as this contributes to the buoyancy control of the animals. The results showed a clear association between lifestyle and skeletal phenotype, and animals that practice aquatic feeding behaviors were found to exhibit higher bone density . Just like the almost solid bones of Spinosaurus or Baryonyx.
” Spinosaurus could have moved through shallow water using a combination of ‘bottom walking,’ like modern hippos, and side-to-side motions of its giant tail. It probably used this means of locomotion not to chase its prey over long distances in open water, but to ambush and catch very large fish such as lungfish or coelacanths that lived in the same environment” , explains Guillermo Navalón from the University of Cambridge, co-author of the work.
Of course, the new study has not convinced the skeptics. Although they approve of Spinosaurus having very dense bones, they say it’s not clear what exactly they were doing in the water. Certainly hippos, for example, spend a lot of time in the water, but they don’t eat in the water.
The authors argue that “the bones don’t lie, and we now know that even the internal architecture of the bones is fully consistent with our interpretation of this animal as a giant predator that hunts fish in vast rivers, using its paddle-shaped tail to propel itself.” .
“I believe that, with this additional line of evidence, speculative notions regarding Spinosaurus as a species of giant mosquito lack evidential support and can be safely excluded,” concludes study co-author Nizar Ibrahim.
Referencia: Matteo Fabbri et al. “Subaqueous foraging among carnivorous dinosaurs”. Nature. DOI: 10.1038 / s41586-022-04528-0
