When did animals start communicating using sound, and why?

A couple of weeks ago, as I wandered through towering ash forests in the foothills of the Dandenong Ranges, I found myself in the middle of an eastern whipbird conversation. It traced the trait back 400 million years to the last common ancestor of four-limbed vertebrates and lungfish, raising the question: did acoustic communication first appear even earlier, underwater, in marine critters? While there were aspects of the katydids' songs that couldn't be elucidated from the fossils — such as their volume, or if they trilled with a particular pattern or tempo — " can conclude that insects … evolved with acoustic communication at least 240 million years ago", Dr Xu says. How insect communication shaped us mammals Michael Engel, an entomologist at the American Museum for Natural History who also worked on the study, says the katydids' calls likely started at a frequency higher than what other animals around them could hear — a bit like how us humans can't hear the high pitch of a dog whistle. While the Chinese katydid fossils show acoustic communication had evolved by at least the early Triassic, phylogenetic studies suggest it arose in Orthoptera around 100 million years earlier.