Modern mammals have unique hearing abilities, able to sense a broad range of volumes and frequencies using middle-ear features, including our eardrums and a few small bones.

A new study from paleontologists at the University of Chicago in the US has revealed these physical features began to emerge nearly 50 million years earlier than we thought.

They found their evidence within a 250-million-year-old fossil of the mammal ancestor, Thrinaxodon liorhinus. Using computed tomography scans of the animal's skull and jaw, they created 3D models that allowed them to simulate how Thrinaxodon's anatomy might have reacted to the different sound pressures and frequencies, using engineering software to see how its bones 'wiggled' in response.

Thrinaxodon lived during the Early Triassic, before the first dinosaurs. It was a cynodont – a close relative of early mammals – with a body that looks somewhere in between a lizard and a fox.

Some of its genes follow the same blueprint modern mammals carry today, and this new study suggests the architecture of its hearing is also something we share.

Early cynodonts had ear bones – the malleus, incus, and stapes – that were attached to their jaw. In later species, these tiny fragments eventually became detached from the jaw to form the distinctly mammalian middle ear.

Before the middle ear and its associated 'tympanic' hearing abilities, animals relied on bone-conducted sound, where nerves carry signals from vibrations in the jawbone to the brain.