This illustration shows a Spinosaurus catching a large sawfish underwater. (David Bonadonna)
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CHICAGO – It has long been thought that dinosaurs were terrestrial creatures—terrestrial creatures that largely stayed out of the water.
a Pioneering discovery In 2014 a Spinosaurus with features suggestive of an aquatic lifestyle — retracted nostrils, short hind legs, fin-like tail and paddle-like feet — challenged this view.
However, whether some dinosaurs were really comfortable in the water or just stood in shallow water and dunked their heads in pursuit of prey. As the heron does Paleontologists have been divided.
In an effort to resolve this heated debate, a group of researchers studied 380 bones belonging to 250 animals — some living, some extinct — including marine reptiles and flying reptiles, as well as mammals, lizards, crocodiles and birds.
“There are certain laws that apply to any organism on this planet. One of those laws is about density and the ability to submerge in water,” said Matteo Fabri, a postdoctoral researcher at Chicago’s Field Museum, in a press release. He was the lead author of the study, which was published Wednesday in the journal Nature.
The study said that bone density can be used as a guide to adaptation to life in the water, even aquatic animals that were not clearly formed for an aquatic lifestyle – such as the hippopotamus – have very dense bones.
The researchers found that spinosaurs — a family of predatory dinosaurs that could reach 49 feet (larger than T. rex) — had dense bones, indicating that they adapted to life in the water. They said it was likely that none of the other 39 dinosaurs the research team examined as part of the study would have been comfortable in the water.
Spinosaurus’ relationship with water
Within the Spinosaurus family, they concluded that Spinosaurus, which has a sail-like feature on its backbone, and its close relative Baryonyx had increased bone density and could swim and fish while submerged underwater — a bit like a crocodile or a hippopotamus. Sucomimus, another closely related dinosaur, had lighter bones that would make swimming more difficult. The study found that it likely lived by water and ate fish, as indicated by its crocodile-like nose and conical teeth, but judging by its bone density, it wasn’t actually swimming.
Thomas Holtz, principal lecturer in vertebrate palaeontology at the University of Maryland, said the study confirmed that the ancestors of Spinosaurus and Baryonyx spent enough time in the water to develop heaviness, to provide stability, in the form of dense bones. However, he said His work on Spinosaurus Show that it is more likely to hit food from above – perhaps from shore, or while lazily sailing on the surface of the water – rather than from diving into the depths.
“The nostrils of a Spinosaurus are not positioned at all as in animals such as hippos and crocodiles, which spend most of their time submerged in water; instead, they are positioned back on the skull as in herons and other animals that feed by dipping them,” he said. Holz, who was not involved in the study: “Snout in water to feed.”
“The new evidence is consistent with his ability to dive, at least for some time. But as we showed in last year’s paper, he couldn’t be a really fast swimmer with that huge sail, at least not in water.”
Jason Ball, assistant professor at Drexel University and director of fossil preparation at the Bighorn Bassin Paleontological Institute, said he would have liked to see more Spinosaurus specimens included in the study.
“Oddball dinosaurs tend to provide insight into the extremes of dinosaur evolution,” said Ball, who was not involved in the research. “The more specimens there are, the better it is to understand how they got so weird.”
“I think this study is good for keeping the movement going but more work is always needed to get a better picture of the life of something very exotic and far in time.”
The researchers, including scientists from the United States, Europe and Morocco, have compiled a database of fragments of femurs and rib bones from a variety of animals to understand whether there is a global association between bone density and behavior.
They cast a wide net. “We’ve included seals, whales, elephants, mice, and hummingbirds. We have dinosaurs of various sizes, and extinct marine reptiles like Mosasaurs and plesiosaurs. We have animals that weigh several tons, and animals of only a few grams. The spread is very large,” Fabry said.
They found that animals that submerge themselves underwater to find food have bones that are almost completely solid, while the cross-sections of the bones of land dwellers look more like cakes, with hollow centers.
They discovered that other dinosaurs, such as the perennial plant-eating sauropods, also had dense leg bones, but other bones were lighter in weight. This was a pattern also seen in very heavy live wild animals such as elephants and rhinos, Fabry said.
The research is an example of a big data approach to paleontology that has yielded intriguing insights into how dinosaurs lived their world — something that is often difficult to ascertain by studying the fossils of individual animals.
Such studies, according to Jingmaye O’Connor, a field museum curator and co-author of the bone density study, which were extracted from hundreds of specimens, are “the future of paleontology.”
“It takes a long time to do, but it has allowed scientists to shed light on large patterns, rather than making qualitative observations based on a single fossil.”
a A study published last year Examination and reconstruction of the inner ears of ancient fossilized beasts and their comparison with the ear canals of living animals. The researchers were able to deduce from this exercise whether the creatures would be night hunters, vigilant fathers, or clumsy flyers.
However, this type of research has limitations, because a single individual feature cannot give a complete picture of an animal’s lifestyle, Holz said.
“Each clue adds to the overall picture. In this particular case, they have provided a fantastic new database of bone density in a variety of animals with different lifestyle habits. So in the future we can now compare other animals with lifestyles that are not well understood,” said Holz.
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