How old did dinosaurs live? Or how long was the general lifespan of dinosaurs? In the realm of living creatures, longevity is shaped by a creatures size and metabolic rate. For example, animals with sluggish metabolisms, such as reptiles, typically enjoy more protracted lifespans compared to warm-blooded birds and mammals of equivalent size. Considering the evidence indicating that many dinosaurs exhibited metabolic traits akin to birds, it's improbable that they shared similar lifespan characteristics with sizable reptiles.

It's plausible that sauropods might have reached ages of 50 to 100 years, while larger theropods likely had somewhat shorter lifespans. Smaller dinosaurs, on the other hand, may have had lifespans ranging from approximately 10 to 20 years.

In 1983, researchers initially identified growth lines within dinosaur bones when examining remains from the Late Jurassic period. These bones belonged to a sauropod called Bothriospondylus, possibly belonging to the herbivorous brachiosaur family. These fossils, discovered over a century earlier, underwent a reevaluation of their age due to this study. It's now believed that this particular Bothriospondylus passed away at the age of 43, although it had only reached around half of its eventual adult length, projected to be between 15 to 20 meters.

In the case of the most substantial and well-preserved Tyrannosaurus rex specimen, housed at the Field Museum in Chicago, scientists estimate its lifespan to be nearly 29 years. However, it's important to note that this T. rex wouldn't have reached full adult size until roughly 20 years into its life.