UnScramble this Word: n e i v a n?

Questions

Nature - What animal has bony plates and rolls up into a ball if it is frightened?

Nature - What has approximately 1/4 pound of salt in every gallon?

Nature - What is the heart rate of the blue whale (in beats per minute)?

Nature - When does the human uterus expand 500 times its normal size?

Nomenclature - Eras are divided into units called ?