Happy alligator with earbuds. Image: Shutterstock
Scientists administered ketigalline alligators and listened to their sounds through earphones to better understand the auditory abilities of dinosaurs.
The Experiment Neuroscience described in a paper published on Monday  Journal of journal was developed to examine the "neural maps" produced by alligators to make noises in theirs To locate habitats. These maps have been vital to many vertebrates and have been developed especially for nocturnal predators such as Barn Owls, as they rely heavily on the sound for locating the prey.
The focus of the study was on a concept called the interaural time difference (ITD), which is the gap in the time of arrival of a sound to each ear. Although this time delay is typically only a few microseconds, it plays a crucial role in allowing animals to recognize where sounds are coming from.
Catherine Carr, a biologist at the University of Maryland, and Lutz Kettler, neuroscientists at the Technische Universität München, have spent years studying how ITD processes help animals such as birds and reptiles locate sounds. Since birds, alligators, and dinosaurs all descended from archosaurs, a lineage that thrived in the Triassic period, the new study provides clues to the hearing systems of dinosaurs by examining their existing relatives.
"Birds are dinosaurs and alligators are their closest living relatives," Carr told Motherboard in an email. "Properties shared by both groups could reasonably be considered as found in extinct dinosaurs, so we assume that dinosaurs can locate sounds."
Previous studies have shown that birds developed a different neuronal process of sound localization compared to mammals. In this study, Carr and Kettler attempted to capture where American alligators fell on the ITD spectrum.
The team injected 40 American alligators from the Rockefeller Wildlife Refuge in Louisiana with ketamine and dexmedetomidine to sedate them. While the animals were anesthetized, Yuin PK2 earphones with horns were inserted into their earlobes. On the heads of the alligators were electrodes to record the neuronal responses of the ear to the sounds and clicks played through headphones.
"We used both tones that the alligator could hear well (about 200 to 2000 Hz) and noise," said Carr. "We have selected the sounds and the noise to provide naturalistic stimuli."
Read more: These alligators have entered deep-frozen mode
The experiment showed that alligators using similar neuronal mapping systems search for birds, despite the large differences in their brain anatomies.
"One important thing we learn from alligators is that head size does not matter how their brains encode the sound direction," Kettler said in an email with the motherboard.
This means that dinosaurs as big as Tyrannosaurus Rex probably used similar auditory mechanisms as birds and alligators to locate sounds. While scientists can not look back in time to gaze into the dinosaur's brain, the surviving relatives of these iconic extinct animals provide an exciting window into the past.
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