According to the Independent, bones belonging to what seems to be two “teenage” Tyrannosaurus rex dinosaurs provide fresh clues as to how these predators grew up to become “plodding, crushing monsters”. The fossil skeletons showed that the juvenile T rex dinosaurs were slender, fleet-footed, had knife-like teeth for cutting food, unlike their lumbering, bone-crushing adult counterparts. Prior to that, it was believed that the bones, which are preserved at the Burpee Museum of Natural History in Illinois, US, belonged to a different dinosaur species, a smaller pygmy relative known as Nanotyrannus. An examination of the microstructures of their tissues within the bones revealed they were part of the T Rex family.
The two fossils examined by the staff at the Burpee Museum of Natural History were given the name Peter and Jane. At its peak, T. rex was 40 feet long. Yet the two small fossils are just a bit taller than a Clydesdale horse and twice its length. According to CNN, researchers sliced into leg bones from the two fossils to understand the age at the time of death for the dinosaurs. Like tree rings, the leg bones of the dinosaurs showed growth rings that put Jane and Petey at 13 and 15 years old, respectively. According to their publication in the journal, Science Advances, the fossils also showed a vascular record, or evidence of blood vessel activity, supporting a rapidly growing young dinosaur. The growth rings revealed how the T-rexes endured years of scarcity. “The spacing between annual growth rings record how much an individual grows from one year to the next,” said Holly Woodward, lead study author at the Oklahoma State University Center for Health Sciences. “The spacing between the rings within Jane, Petey, and even older individuals is inconsistent some years the spacing is close together, and other years it’s spread apart.”
Suggesting that if food was scarce one year, Jane and Petey didn’t grow as much, but they made up for it by growing even more during years when food was abundant. Small, juvenile fossils of larger dinosaurs are equally as important to researchers as adult specimens because paleohistology, or the study of fossil bone microstructure, can actually be used to show how dinosaurs grew as they aged. In the case of T. rex, the dinosaur could take 20 years to reach its massive size, meaning it likely went through a number of dramatic changes over time.
Given how much T. rex changed from juvenile to adult, the researchers believe that the different age groups of these dinosaurs fed on varied prey. Scott Williams, study co-author and paleontology lab and field specialist at the Museum of the Rockies. “That tells us they go through a drastic change when they grow up from these sleek, slender, fleet-footed T. rexes with these wonderful knife-like teeth to these big, monster, plodding crushing tyrannosaurs that we are familiar with. It also tells us these animals probably dominated their ecosystems at all ages.”