By Will Dunham

WASHINGTON (Reuters) - Large, carnivorous dinosaurs reached their large size through very different growth strategies, with some following a slow, steady path and others experiencing a growth spurt in adolescents, according to scientists who analyzed slices of fossilized bones.

The researchers looked at annual growth rings - similar to those of tree trunks - in the bones of 11 theropod species, a large group spanning all large carnivorous dinosaurs, including Tyrannosaurus rex and even birds. The study provides a glimpse into the lives of some of the most formidable predators to ever walk on Earth.

The team examined samples from museums in the United States, Canada, China and Argentina, and even received permission to cut into bone from one of the most famous T. rex fossils in the world. world, known as Sue and kept at the Field Museum in Chicago, using a diamond-tipped saw and drill.

Sue's leg bones - a huge femur and fibula - were used to illustrate that T. rex and its parents - known as tyrannosaurs - experienced a period of extreme growth during adolescence and reached their adult size around the age of 20. Sue, standing about 42 feet (13 meters), lived about 33 years.

Sue lived in South Dakota about a million years before dinosaurs and many other species were wiped out by the impact of an asteroid 66 million years ago.

Other groups of large theropods tended to have more stable growth rates over a longer period. This growth strategy was detected in lines that appeared around the world earlier in the age of the dinosaurs and later were concentrated in the southern continents.

Examples included Allosaurus and Acrocanthosaurus from North America, Cryolophosaurus from Antarctica, and a recently discovered yet unknown species from Argentina that rivaled T. rex in size. The Argentinian dinosaur, belonging to a group called carcharodontosaurs, did not reach full adult size until around 40 and lived to be around 50 years old.

Large theropods share the same general body design, walking on two legs and possessing large skulls, strong and menacing jaws.

the teeth.

"Before our study, we knew that T. rex grew very quickly, but it was not clear if all theropod dinosaurs grew to gigantic size in the same way, or if there were several ways of doing it," said the paleontologist and study leader. author Tom Cullen of the North Carolina Museum of Natural Sciences and North Carolina State University, also affiliated with the Field Museum.

The research was published this week in the journal Proceedings of the Royal Society B.

"Theropod dinosaurs represent the largest bipedal animals to ever live and have also been the dominant predators in terrestrial ecosystems for over 150 million years - more than twice as long as mammals have been dominant," added University of Minnesota paleontologist and study co-author Peter Makovicky.

(Reporting by Will Dunham; Editing by Peter Cooney)