sentences:  After just two years, juveniles were larger than any other predator in the region aside from adult "Albertosaurus", and more fleet of foot than most of their prey animals.This resulted in a dramatic decrease in their mortality rate and a corresponding rarity of fossil remains.Mortality rates doubled at age twelve, perhaps the result of the physiological demands of the rapid growth phase, and then doubled again with the onset of sexual maturity between the ages of fourteen and sixteen.