Eocene Fossil Suggests Owls Were Once Diurnal
"There exists a consensus that owls must have evolved from a diurnal ancestor," said Gerald Mayr, lead author of a new study published in Current Biology. This finding, based on a 47-million-year-old fossil discovered in the Messel Pit in Germany, challenges the long-held assumption that owls have always been creatures of the night.
The specimen, a newly described species named Masillastrix blattophaga, was unearthed in 2025. While the skull is missing, the rest of the fossil remains remarkably intact. Researchers identified a greenish-blue, iridescent cockroach within the bird’s stomach, which served as its final meal. According to the study, the presence of iridescence in the insect—and the owl’s own physical traits—points toward a daytime-active lifestyle.
Clues in the Messel Pit Fossil
The physical characteristics of Masillastrix blattophaga provide significant evidence for its daytime habits. Mayr, who serves as the head of ornithology at the Senckenberg Research Institute and the Natural History Museum Frankfurt, noted that the bird’s upper wing bones, or humeri, are notably stocky. In contrast, modern nocturnal owls possess slim humeri that facilitate silent flight, an adaptation that provides a stealth advantage in low-light environments.
For a bird hunting in the daylight, the need for silent flight is reduced because predators can be easily spotted. The study also highlights that the Messel owl measured less than 5 inches long. Researchers found a matching iridescent cockroach in sediment just a few feet from the bird, which allowed them to confirm the contents of the stomach.
Timeline of Nocturnal Evolution
The discovery helps narrow the window for when owls transitioned to their modern nocturnal behavior. Based on the fossil record, Mayr estimates that the shift to a night-active lifestyle likely occurred between 47 million and 35 million years ago. While the oldest known owl fossil, Ogygoptynx wetmorei, dates back approximately 60 million years, it is not until the Late Eocene—about 35 million years ago—that the fossil record begins to show owls with the elongated humeri typical of modern species.
The researchers acknowledged that the fossil record for early owls remains sparse, often relying on isolated bones. Consequently, the transition remains an estimate rather than a definitive timeline.
Unanswered Questions About Nighttime Behavior
The primary mystery remains why owls transitioned to hunting at night. Previous theories suggested that owls adopted this behavior to avoid competing with other diurnal birds of prey or to exploit the rise of nocturnal mammals. However, the study points out that both groups proliferated significantly later, between 20 million and 25 million years ago, making these drivers less likely to have triggered the initial change.
"We still know so little about the early evolution of modern birds," Mayr noted, emphasizing that each new fossil discovery carries the potential to overturn established theories in the field.
Common Questions Regarding the Messel Owl
When was the Masillastrix blattophaga fossil found?
Researchers unearthed the fossil in 2025 at the Messel Pit in Germany, a site renowned for its well-preserved Eocene epoch specimens.
Why do scientists believe this specific owl was active during the day?
The study cites the owl’s stocky humeri, which differ from the slim wing bones of modern nocturnal owls, and the presence of an iridescent cockroach in its stomach as evidence of a diurnal lifestyle.
How does this discovery change the understanding of owl evolution?
It provides concrete evidence that owls were not nocturnal 47 million years ago, shifting the focus toward the period between 47 million and 35 million years ago as the likely timeframe for the evolution of the nocturnal lifestyle.
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