The rooted cheek teeth have occlusal patterns dominated by re-entrant enamel folds. In North American porcupines the female reaches sexual maturity at about 18 months old. The estrous cycle is 29 days, and these animals have more than one period of estrus in a year. The females form a copulatory plug because they have a vaginal closure membrane. The gestation period averages 210 days.
Females give birth to their young in tree cavities.
There is usually only one young produced, although rarely there can be twins. In North American porcupines the weight of the precocial newborn is 21 ounces. The newborn animals feed on their own after the first few days, although lactation continues for 56 days. Porcupine young are born able to walk with their eyes open. They display typical defense reactions and within a few days are able to climb trees.