Prehistoric Soundscape

Imagine you’re being chased by a T. rex. What would you hear? Some very big footsteps. Some very heavy breathing. Someone screaming—maybe that’s you. What else? Scientists have been trying to determine what the prehistoric world sounded like by studying the sounds of modern animals. Sounds of aggression, like roars and screams. Sounds of communication, like birdsong or a wolf howl. Perhaps most amazing, echolocation—used by bats and whales to find prey and avoid obstacles. The organs required to make, and hear, these sounds had to evolve sometime. So scientists went looking for them in the fossil record. And here’s what they found: For 90% of Earth’s history, the only sounds were natural phenomena, like waves and thunder. That would have made little difference to early life forms—because none of them could hear. Then around 400 million years ago, crustaceans started making clicking sounds. Early fishes, looking for a meal, developed the ability to hear them. It took land animals a long time to catch up. But by 200 million years ago, insects were chirping, early birds were honking, and, to track them, predators developed the tympanic eardrum. So what would you have heard from that tyrannosaur? Well, not much. He might have been able to huff or hiss. But with no vocal cords, he couldn’t roar like in the movies. And he’d probably be too far behind you anyway. Turns out T. rex may have been much slower than we thought. But that’s a story for another EarthDate.