Daohugou, ~165 Ma — a forest you can walk around in, in the dark, by ear↩ mino.mobi
Nine ensiferans sang in this forest, and we know roughly what each of them
sounded like. Five called in low pure tones below 7 kHz; three sang above
10 kHz; and one — Sigmaboilus peregrinus — sang at 22.5 kHz, above
the top of human hearing. That is the oldest ultrasonic communication known
from any animal, about a hundred and ten million years before the first bat.
Press play and walk about. Every call here is synthesised
from its own instrument — the tooth-by-tooth spacing of that species'
fossilised file, driving a wing resonator at its published sharpness — and
then thrown across the air by ISO 9613, with the distance, the weather and
the leaves all taken off it.
off — ultrasound is being rendered at its true pitch, where you almost certainly cannot hear it
loading the engine…
The plot
Click or drag the forest to walk there · WASD / arrows to step
(hold shift to stride) · click a dot to select that species.
The gap this closes
Katydid ultrasound has usually been explained as an answer to bats. These
fossils are a hundred and ten million years too early for that, and Gu
et al. say so plainly: they reject the hypothesis that bats
were the sole driver of ultrasound evolution in katydids, and propose
instead that early mammals and non-mammalian ancestors were already
listening in. Bats, in their phrase, emerged into a soundscape already busy
with ultrasounds.
That is why the who is listening control matters more than
it looks. Switch between an early mammal and an archosaur and watch the
ultrasonic circle swell and vanish: against one ear the pitch bought no
privacy at all, against the other it bought a private channel. The fossils
do not settle it. The physics only tells you what each answer costs — and
the Q panel shows the other half of the same defence, the
one that does not depend on pitch at all.