Tyrannosaurus growth

Dinosaurs grew very large in a relatively short period of time, and their bodies changed as they matured. This happened in T. rex too, but with a twist.

"Jane" a Juvenile Tyrannosaurus (image Wikipedia)

That Dinosaurs could grow to enormous size is common knowledge, but they were surprisingly small when they hatched. Even the largest known Dinosaur egg is no more that 25 by 30 centimetres. No T. rex egg is known, so we don't know exactly how big they were when hatching, but they were probably about the size of a chicken.

The growth pattern of Dinosaurs can be roughly summarized as a number of years of slow growth, followed by rapid growth until maturity and gradual growth until death. Depending on the size of the Dinosaur it could take anywhere from 2 years for the smallest species, to 15 years for the gigantic Sauropods to reach maturity (quite amazing if you consider the size of the largest Sauropods). 

Tyrannosaurus had a surprising twist on this pattern. Much like humans T. rex did not start its fast growth until around twelve years old, and would then grow rapidly until reaching maturity at 18 or 19 years old. Compare that to the basal Tyrannosaurid Guanlong which was found to have been mature at a mere seven years of age.

It has been suggested that the reason that Tyrannosaurus enjoyed such a long infancy and adolescence was that the juveniles filled the ecological niche normally occupied by medium-sized predators. So far no medium-sized carnivores have been found that shared an environment with T. rex. The "King the Tyrant Lizards" was definitely the top-predator in it's environment, it was probably also the dominant medium-sized predator.

"Sue" a mature Tyrannosaurus (image Wikipedia)

Despite the long years of youth Tyrannosaurus was not a particularly long-lived species. Sue, the oldest  known specimen, was 28 years old when she died. A ripe old age for a T. rex. Over half the known fossils were animals that had died within six years of reaching maturity.

Like most Dinosaurs Tyrannosaurus rex grew fast, and died young.