A tiny dinosaur hunted in the dark and heard better than an owl

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That’s one of the findings of two groundbreaking studies released Thursday that examined and reconstructed the inner ears of ancient fossilized beasts and compared them to the ear canals of living animals.

The results offer intriguing insights into how dinosaurs may have experienced their world, especially whether they were nocturnal hunters, attentive parents, clumsy travelers, or dwellers of the earth.

“Of all the structures that can be reconstructed from fossils, the inner ear is perhaps the one that most resembles a mechanical device,” said paleontologist Bhart-Anjan Bhullar, lead author of one. new studies published in the journal Science, in a press release.

“It is entirely dedicated to a particular set of functions. If you are able to reconstruct its shape, you can reasonably draw conclusions about the actual behavior of extinct animals in an almost unprecedented way,” said Bhullar, assistant professor of Earth and Planetary Sciences and an Assistant Curator at the Yale Peabody Museum of Natural History.

It & # 39; s  is about  a reconstruction of  artist of Shuvuuia deserti by Viktor Radermaker.
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Both studies used computerized tomography (CT) scanning technology to scan rock and bones to visualize and model the inner ear, which is located deep within an animal’s skull. This means that it is often well preserved and protected in fossils, but also difficult to access for paleontologists.

“Until recently, the advances presented by these teams of authors were unthinkable, as many aspects of internal anatomy and certainly their connection to habits such as parental care and patterns of daily activity were out of reach, ”said Lawrence Witmer, professor of paleontology. and anatomy in the Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, in an article accompanying the studies. Witmer was not involved in the research.

Night hunter

The traditional scientist the opinion of the dinosaurs was that they were mainly active during the day. Anatomical evidence that would suggest sensory innovations – like acute sight and hearing – necessary for hunting prey at night has gone unnoticed in the fossil record and has been clouded by a lingering assumption that dinosaurs were cold-blooded creatures.
In the second study, Lars Schmitz, associate professor of biology at the WM Keck Science Center at Claremont McKenna, Pitzer, and Scripps Colleges, collaborated with a team of international researchers to collect detailed information on the relative sizes of the eyes and inner ears of nearly 100 species of living birds and extinct dinosaurs.
Scientists specifically looked at the lagena, which processes sound information entering the ear. (This structure corresponds to the cochlea in mammals and modern-day birds and crocodiles.) The team also measured the ring of bones that make up the orbit. The larger the eye, the larger the pupil, which means more light can enter, which allows for better night vision.
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Researchers found that a small dinosaur, Shuvuuia deserti, had proportionately larger pupils than any living bird or dinosaur and an inner ear similar to that of a barn owl. These characteristics suggested that it was a highly specialized night hunter, said. Therapod – the same family as T. rex and a lineage that eventually evolved into living birds, the chicken-sized creature is believed to have lived in very dry habitats in what is now Mongolia about 66 million years old.

“It’s a little strange dinosaur”, Schmitz mentionned. “What we are seeing are very large pupils, an elongated internal ear canal. Hypersensitive eyes. It really rivals today’s nocturnal specialists like barn owls and bats.”

“We think he would have stalked his prey – small mammals – at night when the temperatures were cooler.”

The team found that many carnivorous theropods such as the Tyrannosaurus had optimized daytime vision and above-average hearing, likely to help them hunt. Other dinosaurs such as Velociraptor, the predatory carnivore made famous by the “Jurassic Park” movie franchise, may have been active at dusk, Schmitz mentionned.

Shuvuuia deserti lived in very dry habitats in what is now Mongolia about 66 million years ago.

Dedicated parents?

Using computed tomography technology to determine its three-dimensional shape, Bhullar’s study compared the inner ear of 128 different living and fossilized animals, including Hesperornis, an 85-million-year-old bird species that has teeth. and a beak; the Velociraptor; and the flying pterosaur Anhanguera.

Researchers have found groups of different species with similar inner ear traits. The clusters, the team said, corresponded to different ways the animals moved and viewed the world.

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For example, one group included restless or clumsy fliers like modern chickens and ducks, which fly in fast, straight gusts, and seabirds and vultures. The inner ears of the bird-like dinosaurs called troodontids, pterosaurs, flying reptiles, Hesperornis and Archeopteryx “dino-bird” were part of this group, suggesting that they had a simple flight ability but perhaps did not have any. not be flown gracefully through the air.

Bhullar and his team at Yale also identified a group of a large group of species, including all modern birds and crocodiles, known as archosaurs, which had a similar elongation in the lower part of the inner ear – the cochlear system – which has been associated with greater hearing sensitivity, especially at higher locations. The living animals in this group have a very complex vocal repertoire, explained Bhullar, who said the common ancestors of crocodiles and birds probably sang too.

While this could be explained as an evolutionary adaptation to locate prey, avoid predators or communication, the authors said their analysis suggested it was more likely related to parental care – allowing the creatures to respond to their acute calls. offspring to grab their attention (think birds chirping in a nest).

Recent technological advancements, like the CT scans used in these studies, offer scientists more possibilities for future discoveries, Witmer said. “Teeth and limbs will always provide clues to reconstruct evolutionary histories,” he said. “But relatively new anatomical players like the inner ear and the bony eye rings are opening new windows to the past.”

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