Dinosaurs Inside and Out

Growing Bones

When did primary bones develop during a dinosaur’s life?

Scientists believe primary bones, also called fibro-lamellar bones, were formed during the rapid growth phase of a dinosaur’s life—in particular, when the dinosaur was young. These bones were very similar in structure to bones with blood vessels found in birds and mammals; the dinosaur’s primary bones also contained blood vessels, which helped them to grow fast. These tissues are especially noticeable in fossil dinosaur leg bones.


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