Tyrannosaurus rex took 40 years to reach full size

New analysis of bone growth rings shows the'tyrant lizard king' grew very slowly. Breakthroughs, discoveries, and DIY tips sent six days a week. Based on the annual growth rings (like those on trees) within fossilized leg bones, scientists estimate that usually reach adulthood at around 25 years old. However, new research argues that their growth phase lasted significantly longer. They may have become fully grown--approximately eight tons--after 40 years.