"Jane" and "Petey" reveal mystery of how big T. rex grew

T. rex, the most famous dinosaur in the world, would have been slightly taller than a draft horse and twice as long

In the famous movie “Jurassic World”, the film's creators portrayed pterosaurs as huge dinosaurs flying in the air with talons that can swipe people from the ground and throw them away, although the last pterosaur was estimated to live millions of years before the evolution of humans.
While the tyrannosaurus rex (T. rex) is a very popular and legendary predator with a length of about 12 metres with a longitudinal head of up to five metres, containing strong teeth that can easily crush bones, we know relatively little about how large it was.
In a new study published in the journal Science Advances on Wednesday, a research team led by the Oklahoma State University Center for Health Sciences examined the bones of two non-adult and medium-sized pterosaurs to explore more information about the legendary and ancient creature.
In early 2000s, the fossils of two comparatively small T. rex skeletons were collected from Carter County, Montana, by Burpee Museum of Natural History in Rockford, Illinois.
Scientists nicknamed the two skeletons as “Jane” and “Petey", noting that the tyrannosaurs would have been slightly taller than a draft horse and twice as long.
Lead author of the study Holly Ballard, Ph.D., from Oklahoma State University Center for Health Sciences said that many museums used to collect the biggest and most impressive fossils of a dinosaur species for display.
“The problem is that those smaller fossils may be from younger animals. So, for a long time we've had large gaps in our understanding of how dinosaurs grew up, and the T. rex is no exception,” she added.
Ballard told Daily News Egypt that the tyrannosaurus rex is the most famous dinosaur in the world, but we know relatively little about how it grew so big. To help answer this question, the bone tissue microstructure of two half-grown T. rexes was examined. Bone microstructure reveals how fast an animal was growing, how old it was when it died, and whether or not it was an adult.
"When we looked at the leg bone microstructure in these two dinosaurs, we found they were growing quickly, showed no sign of approaching adult size, and were about 13-15 years of age. Taken together, our results refute the hypothesised presence of a smaller tyrannosaur living alongside the T. rex called ‘Nanotyrannus'. Instead, these smaller tyrannosaurs were juvenile T. rexes," Woodward noted.
She explained further that because the T. rex took about 20 years to reach adulthood, the paper's results support a growing body of evidence that the T. rex was able to exclude other carnivores from the mid-sized carnivore niche, giving it the ruling Hell Creek Formation that made it such a apex carnivore.
In order to get to the findings of the study, the researchers used bone histology, the study of bone tissue microstructure. From the microstructure, the scientists were able to obtain a cross-section from the leg bones of each tyrannosaur.
"We glued this cross-section to a glass slide and polished it down on a grinder-polisher wheel until the fossil section was so thin that light can pass through. This usually occurs at about 60 micrometres in total thickness. To view the bone tissue, we used a polarising microscope and a total magnification between 20x and 100x. At this level we observed bone tissue organisation, blood vessel canals, and the cavities that housed bone cells," Woodward added.
The results of this study are so important because this is the first time the bone histology of a juvenile T. rex has been described in detail, and the conclusions help add to our understanding of the most famous dinosaur in the world.
According to researchers, we have known very little about how the T. rex grew, and this research helps fill in some of those gaps. It also shows us that the T. rex was very successful ecologically: although it took 20 years to reach adult size, this allowed for the T. rex to exploit various ecological carnivore niches as it grew bigger. Essentially, the T. rex only had competition for a certain food source from other T. rexes of the same size.
Ballard said that the results of the study are part of a larger study she and her team began in 2014, to explore in detail the growth dynamics of the Tyrannosaurus rex and its close relatives. The results they report on here will be incorporated into this larger study.
One point that wasn't discussed in detail in the paper is that right now, only two juvenile T. rexes have been histologically examined in any detail (the two in this study), but it is important for future studies to histologically examine more specimens, both older and younger, to complete the picture. Although histology removes a part of bone for analysis, scientists still know nothing about T. rex growth rates or ages.