This is one of the results of two groundbreaking studies published Thursday examining, reconstructing and comparing the inner ears of ancient fossilized animals with the ear canals of living animals.
The results offer fascinating insights into how dinosaurs may have experienced their world, including whether they were nocturnal hunters, observant parents, awkward fliers, or land rubbers.
“Of all the structures that can be reconstructed from fossils, the inner ear is perhaps the most similar to a mechanical device,” said paleontologist Bhart-Anjan Bhullar, lead author of one of the new studies published in Science. in a press release.
“It is so wholly devoted 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 almost unprecedented ways,” said Bhullar, an Earth and Assistant Professor Planetary Sciences and an assistant curator at the Yale Peabody Museum of Natural History.
Both studies used computed tomography (CT) scanning technology to look through rocks and bones, and to visualize and model the inner ear, which is located deep inside an animal’s skull. This means that it is often well preserved and protected in fossils, but it is also difficult to access for paleontologists.
“Until recently, the advances made by these teams of authors have been unthinkable as many aspects of internal anatomy, and certainly its connection to habits such as parental care and daily activity patterns, have been unreachable,” said Lawrence Witmer, professor of paleontology and anatomy at Heritage College’s Institute of Biomedical Sciences of Ohio University’s Osteopathic Medicine in an article accompanying the studies. Witmer was not involved in the research.
Hunter of the night
The traditional scientific Dinosaurs believed that they were mostly active during the day. Anatomical evidence that would suggest it sensory innovations – like sharp vision and hearing – needed to hunt prey at night, went undetected in the fossil record and was In the second study, Lars Schmitz, Associate Professor of Biology at WM Keck Science Center at Claremont McKenna, Pitzer, and Scripps Colleges, worked with a team of international researchers to collect detailed information about the relative sizes of the eyes and inner ears of nearly 100 live birds – and extinct species of dinosaurs. The scientists looked specifically at the Lagena, which processes incoming sound information in the ear. (This structure corresponds to the cochlea in mammals and modern birds and crocodiles.) The team also measured the bone ring that makes up the eye socket. The larger the eye, the larger the pupil, which means more light can penetrate – which allows for better night vision.
The researchers found that a small dinosaur, Shuvuuia deserti, had pupils that were proportionally larger than any living bird or dinosaur, and an inner ear that resembled that of a barn owl. These characteristics indicated that it was a highly specialized nocturnal hunter. As a Therapod – the same family as the T. rex and a lineage that ultimately evolved into live birds – the chicken-sized creature would have lived in very arid habitats in what is now Mongolia about 66 million years ago.
“It’s a strange dinosaur,” said Schmitz said. “What we see are really large pupils, an elongated inner ear canal. Hypersensitive eyes. It can really compete with the nocturnal specialists like barn owls and bats.”
“We believe it would have chased its prey – small mammals – at night when the temperatures were cooler.”
The team found that many carnivorous theropods, such as Tyrannosaurus, had daytime eyesight and above-average hearing, presumably to help them hunt. Other dinosaurs such as Velociraptor, the predatory meat eater made famous by the Jurassic Park film franchise, may have been active in Schmitz at dusk said.
Bhullar’s study used CT scan technology to determine its three-dimensional shape and compared the inner ear of 128 different living and fossilized animals, including Hesperornis, an 85-million-year-old bird-like species with teeth and beak. the velociraptor; and the flying pterosaur Appendixuera.
The researchers found clusters of different species with similar inner ear features. The clusters, according to the team, correspond to different ways in which animals move around the world and perceive them.
For example, one cluster included restless or awkward fliers like modern chickens and ducks that fly in quick, straight bursts, as well as sea birds and vultures. Called the inner ears of bird-like dinosaurs, troodontids, pterosaurs, flying reptiles, Hesperornis, and the “dino-bird” Archeopteryx, they fell into this group, suggesting that they had easy flight ability but may not have flown gracefully in 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 stretching of the lower part of the inner ear – the cochlear system – that has been associated with greater hearing sensitivity in particular at higher pitches. Live animals in this group have a very complex vocal repertoire, explained Bhullar, who said the common ancestors of crocodiles and birds likely sang too.
While this could be explained as an evolutionary adaptation for finding prey, avoiding predators, or communicating, the authors said their analysis suggested that this was more related to parental care – giving the creatures the high shouts their offspring can react to attract their attention (think of chirping baby birds in a nest).
Recent technological advances, like the CT scanning used in these studies, offer scientists more opportunities for future knowledge, Witmer said. “Teeth and limbs always provide clues for reconstructing evolutionary history,” he said. “But relatively new anatomical players like the inner ear and the bony dark circles open new windows into the past.”