Why have so many modern-day mammals evolved adaptations suited for the night? The answer might very well be dinosaurs, according to new research.
A study published in the journal Nature Ecology & Evolution suggests that the threat of dinosaurs, who ruled the world during the daytime more than 65 million years ago, encouraged mammals to only come out under the dark of night.
This idea – known as the “nocturnal bottleneck hypothesis” – has intrigued scientists for years, but it’s been difficult to prove by direct means. The new study explores the hypothesis further by analyzing the behavior patterns of 2,415 mammal species, and then using computer models to predict the behavior of their ancestors. The international team of researchers classified each species’ behavior into five categories:
- Nocturnal – active at night
- Diurnal – active in the day
- Cathemeral – active during both day and night
- Crepuscular – active only at twilight, around sunrise and sunset
- Ultradian – active in cycles for several hours at a time
Focusing on the first three categories – nocturnal, diurnal, and cathemeral – the team found that most of the ancestors of modern-day mammals were likely nocturnal, but probably switched to other activity patterns after the dinosaurs died off.
“On balance, our evidence suggests that mammals remained nocturnal throughout the Mesozoic,” the authors…
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