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According to scientists who analyzed slices of fossilized bones, large carnivorous dinosaurs reached their great size through very different growth strategies, with some taking a slow and steady path and others experiencing a teenage growth spurt.
The researchers examined annual growth rings, similar to those in tree trunks, in the bones of 11 theropod species, a large group that includes all large carnivorous dinosaurs, including Tyrannosaurus rex and even birds. The study provides insight into the lives of some of the most fearsome predators to ever walk the Earth.
The team examined samples from museums in the United States, Canada, China and Argentina and even received permission to cut bones from one of the most famous T. rex fossils in the world known as Sue and housed at the Field Museum in Chicago, using a saw and diamond-tipped drill.
Sue’s leg bones – a huge femur and fibula – helped illustrate that T. rex and its relatives – known as tyrannosaurs – experienced a period of extreme growth in adolescence and reached adult size around 20 years. Sue, who measures around 42 feet (13 meters), lived around 33 years.
Sue inhabited South Dakota about a million years before dinosaurs and many other species were wiped out by an asteroid impact 66 million years ago.
Other groups of large theropods tended to have more constant growth rates over a longer period of time. That growth strategy was detected in lineages that arose around the world at the beginning of the dinosaur era and subsequently concentrated on the southern continents.
Read also: Fossil reveals a “dandelion toucan” who lived with dinosaurs
Examples included Allosaurus and Acrocanthosaurus from North America, Cryolophosaurus from Antarctica, and a recently discovered yet unnamed species from Argentina that rivaled T. rex in size. The Argentine dinosaur, from a group called carcharodontosaurs, did not reach its full adult size until age 40 and lived to be around 50.
Large theropods share the same overall body design, walk on two legs, and boast large skulls, strong jaws, and menacing teeth.
“Prior to our study, T. rex was known to grow very rapidly, but it wasn’t clear whether all theropod dinosaurs reached gigantic sizes in the same way, or if there were multiple ways it was done,” said the paleontologist and lead 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 that ever lived and have also been the dominant predators in terrestrial ecosystems for more than 150 million years – more than twice as long as mammals have been dominant,” added the University of Delphi paleontologist. Minnesota and study co-author Peter Makovicky.
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