Frankfurt, 03.11.2026 (PresseBox) - An exceptionally well-preserved, approximately 47-million-year-old owl fossil from the UNESCO World Heritage Site Messel provides new clues as to when owls became nocturnal. The newly described species Masillastrix blattophaga was likely still diurnal?as indicated by an iridescent cockroach in its stomach, as well as the structure of its feathers and wing bones. In their new study, published today in the journal ?Current Biology,? the Senckenberg researchers speculate that nocturnal behavior in owls only developed toward the late Eocene, some 47 and 34 million years ago.

For most owls, their day begins when darkness falls. Thanks to their exceptionally keen hearing, they can locate their prey even in dim light, and their uniquely designed wings allow them to glide almost silently through the night. ?It is still unknown when, in the evolutionary history of owls, the transition from a diurnal to a nocturnal lifestyle took place,? explains Dr. Gerald Mayr of the Senckenberg Research Institute and Natural History Museum in Frankfurt, and he adds, ?This is partly due to the fact that, although quite a number of owl fossils have been found, most are represented by only a few isolated bones.?

The situation is different for the fossil that was recovered during the 2025 excavation season in the German fossil site Messel and has now been described as Masillastrix blattophaga by the Frankfurt-based ornithologist and his colleagues. ?Except for the skull, the bird?s skeleton is complete and exceptionally well-preserved,? says Mayr. ?It is an owl from the Middle Eocene that measures about 12 centimeters in length and lived some 47 million years ago. It is only the second owl species known from the Messel site, whose fossiliferous sediments were deposited in forested environment.?

The preservation of this owl fossil is unprecedented: its wing and tail feathers are preserved and in the stomach area researchers found the remains of a greenish-blue iridescent insect?apparently the bird?s last meal. ?The shape and structure of the wing remnants?including their strong longitudinal veins and numerous transverse veins?indicate that the insect is a fossil cockroach,? explains Dr. Sonja Wedmann, head of the Messel excavation at the Senckenberg Research Institute and Natural History Museum in Frankfurt, and she adds, ?At the same site, we found a very similar?though much better-preserved?cockroach just a few meters away from the owl fossil. This confirms that the greenish-blue iridescent remains in the owl?s stomach are indeed part of a cockroach wing.?

In extant cockroaches and other insects, iridescent wings are associated with a diurnal lifestyle. ?Therefore, the cockroach found in the little owl?s stomach provides an important clue about the bird?s own period of activity,? concludes Mayr. And it is not only the consumed insect that argues against the newly discovered Messel owl being nocturnal; its flight feathers also lack the typical characteristics of today?s nocturnal owls. ?Furthermore, the fossil owl?s humerus is significantly more abbreviated than that of modern owls. This suggests that its wings were not yet as long and adapted for silent flight,? adds Mayr.

Based on the known fossils, the exact transition of owls from a diurnal to a nocturnal lifestyle remains difficult to pinpoint. However, the shape of the humerus provides an important clue. The oldest owl with humerus proportions typical of modern owls lived in France about 35 million years ago. According to the research team, this suggests that nocturnal activity likely developed between the middle and late Eocene, i.e., about 47 to 34 million years ago.

?The discovery of this new owl species impressively demonstrates what makes the Messel Pit so unique: its exceptional preservation environment have kept intact for over 47 million years even the finest details, such as feathers and stomach contents. This allows us now to not only get an idea of what the bird looked like, but also to understand how it lived and to narrow down the time period during which owls developed their nocturnal lifestyle,? adds Wedmann in conclusion.

Publication: Gerald Mayr, Lucia ?mídová, Adrian Richter, Sonja Wedmann (2026): Evidence for diurnal habits in an exceptionally preserved Eocene owl, Current Biology. https://doi.org/10.1016/j.cub.2026.09.079