Dinosaurs had bones in their eyes. You don’t, and nor does any other mammal, from dogs to whales to elephants. We’re the odd ones out. Birds, lizards, turtles and fish all have a ring of thin bony plates sitting in the white of the eye, holding a big eyeball steady so it can focus. Because it’s bone, it sometimes fossilises, and that matters, because the age of the dinosaurs lasted around 160 million years and roughly half of it happened in the dark.

This week’s word is sclerotic ring. Sclerotic comes from a Greek word meaning hard, and the ring is usually made of 10 to 15 overlapping plates, arranged like the stones in an archway. Measure the hole in the middle, like the hole in a Polo mint, and compare it with living animals. A big hole lets in lots of light, which suits an animal that was up at night. A small hole means a daytime animal. It works just like a camera.

Lauren and Cassius Morrison hear from Dr Stephan Lautenschlager, a palaeontologist at the University of Birmingham who uses computer models to work out how dinosaurs looked, lived and behaved. Bigger eyes mean bigger lenses and room for more light-sensing cells, so bigger eyes see better. The middle of a Jurassic night was probably busy, with some dinosaurs out in the day, some at night and some at dawn and dusk, which may have been ideal hunting conditions for meat-eaters. He explains why owls hear so well (one ear sits higher than the other), what the optic lobes in a dinosaur’s brain tell us, and admits that nobody knows how dinosaurs slept or what colour their eyes were.

Fresh from the Dig names the owl dinosaur: Shuvuuia, a chicken-sized dinosaur from the Mongolian desert with huge eyes and an inner ear to match a barn owl’s. Then a study that compared the eye rings of dozens of fossil animals with living ones: small meat-eaters were mostly out at night, big plant-eaters snacked around the clock, and big predators came out at dawn and dusk. And birds can see ultraviolet light that humans can’t, so dinosaurs may have been far more patterned than any picture shows. In the Dino-Mite Question, Noor, nine, from Birmingham, asks whether dinosaurs slept standing up or lying down. The best clue is Mei long, the “sleeping dragon”, a duck-sized fossil from China found curled up with its head tucked in, just like a bird.

Then it’s Build a Dino Lab. Week nine is the eyes: small, cheap daytime eyes, or big eyes, a wide sclerotic ring and big optic lobes for working in the dark. Big eyes win, with a twist. Our dinosaur’s reflective skin, chosen back in episode five, would shine like a headlight under the moon and stand out at midday, so it hunts at dawn and dusk, when the night animals are going to bed, the day animals are only just getting up, and everyone is half asleep. Lions and foxes do the same. Next week, arms.

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