 Paleontologist Gregory Erickson and colleagues have studied the growth and life history of tyrannosaurids . Analysis of bone histology can determine the age of a specimen when it died . Growth rates can be examined when the age of various individuals are plotted against their size on a graph . Erickson has shown that after a long time as juveniles , tyrannosaurs underwent tremendous growth spurts for about four years midway through their lives . After the rapid growth phase ended with sexual maturity , growth slowed down considerably in adult animals . A tyrannosaurid growth curve is S @-@ shaped , with the maximum growth rate of individuals around 14 years of age . 
