47-million-year-old owl Masillastrix blattophaga had an iridescent cockroach in its stomach

The remains of an owl chick, Masillastrix blattophaga, lie in the shale of the Messel Pit in Germany, according to pravda.ru. The bird was only 12 centimetres long and lived 47 million years ago pravda.rupravda.rupravda.ruOpen source ↗. Its stomach preserved its last meal: a cockroach with a greenish-blue iridescent sheen.

Iridescent colouring of this kind is typical of insects that are active in daylight. If the owl hunted such a cockroach, it most likely saw it in sunlight rather than in the dark.

What the stomach contents and bones show

A single meal could be explained by hunting at dusk. So palaeontologists from the Senckenberg Institute also examined the skeleton. In modern nocturnal owls the humerus bones are thin, which is linked to silent flight: the birds need to approach prey without a sound.

In Masillastrix blattophaga the humerus bones were short and massive. This wing architecture is typical of diurnal predators, which do not need to hide the sound of their approach pravda.rupravda.rupravda.ruOpen source ↗. Earlier finds point the same way: bony ridges above the eye sockets of some fossil owls could have worked as visors shielding the eyes from bright sun.

When owls moved to the night shift

The Messel owl is evidence of a daytime lifestyle 47 million years ago. Classic nocturnal owls appear about 35 million years ago. The transition to night activity therefore falls between these two dates.

Two earlier explanations held that owls moved into the night to avoid competition with diurnal predators, or to exploit a surge in nocturnal mammals. The data show that both groups spread widely much later, about 20 to 25 million years ago, so the displacement scenario does not fit the timeline.

Gerald Mayr and colleagues, in a paper in Current Biology, state that the more precisely the timing of the shift in activity is determined, the clearer it becomes that the reason for the owls' nocturnal lifestyle lies in something not yet identified pravda.rupravda.rupravda.ruOpen source ↗.