Attempts to duplicate the teeth marks left by juvenile T. rexes in ancient bones indicate that these young predators possessed a fairly strong bite – but one that paled in comparison to their parents’ formidable chomp.
Previous attempts to estimate the biting force generated by juvenile T. rexes focused on musculoskeletal modelling, which employs anatomical and physical concepts to provide a greater range of possibilities.
For the latest study, published Wednesday in the journal PeerJ, scientists ditched the models and opted for experimentation.
“Musculoskeletal modeling provides broad ranges of movement … whereas experimentation replicating the outcomes of direct behavior such as puncture marks provide specific estimates of necessary physical forces to perform a single task,” study co-author Jack Tseng told UPI in an email.
While modeling can help with comparing different fossil species, Tseng said experimentation can provide insights into the behavior of individuals or single species.
“The presence of puncture marks attributed to juvenile tyrannosaurs afforded an opportunity to use experimentation to get at the bite force question for these young predators,” said Tseng, an assistant professor of integrative biology at the University of California, Berkeley.
A number of studies have suggested that behavior and ecology of the juvenile T. rex was quite different than those of an adult.
One study even estimated that the prevalence of teenage T. rexes was to blame for a lack of diversity among smaller dinosaurs during the Cretaceous.
More accurate estimates about a young T. rex’s real world bite force can help scientists understand the ecological differences between juvenile and mature T. rexes.
Tseng said the study’s findings are consistent with the idea of juvenile tyrannosaurs being ecologically distinct from their adult counterparts.
He noted, however, that while the new bite force estimates bring teenage T. rexes closer to adults, researchers remain unsure “just how ecologically different or similar” differently aged individuals may have been.
“The fact that geologically older deposits contained higher diversity of smaller bodied dinosaurs strongly suggest those predatory niches were successful ways to make a living,” Tseng said. “If so, juvenile T. rex individuals remain the best candidates for having filled those ecological roles during late Cretaceous times.”
In the lab, Tseng and his research partners attempted to replicate the teeth marks left in the well-preserved skull of a juvenile T. rex — specifically, an upper tooth-bearing element called the maxilla, which is thin but quite dense.
Scientists forged a metal replica of a saber-shaped tooth, attached it to a mechanical testing frame and clamped it onto cow bones to see how much force was required to match the depth of bite marks in the fossil bones.
“We also used a bitten tail vertebra from an Edmontosaurus which is considerably softer,” lead author Joe Peterson, a professor of geology at the University of Wisconsin, Oshkosh, told UPI in an email.
“Presumably, a juvenile T. rex didn’t use its maximum potential to bite both of these just as we don’t always bite down as hard as we can when we are eating. But by replicating bites in bones of various density, we could see a range of bite force potential in a juvenile tyrannosaur,” Peterson said.
The tests showed young T. rexes were able to generate up to 5,641 newtons of force — more powerful than the bite of a hyena but not quite as forceful as the chomp of a crocodile. Previous studies suggest the jaws of adult T. rexes could generate upwards of 35,000 newtons of force.
Previous modeling efforts have put the bite force of young T. rexes at somewhere around 4,000 newtons. The latest findings suggest they were a bit more powerful.
The data generated by the latest experiments allowed researchers to begin building a bite force curve for juvenile T. rexes, which can provide further context for broader T. rex growth curves.
While more analysis is necessary, the research supports the notion that juvenile T. rexes are ecologically distinct from their parents, and perhaps occupied a variety of niches over the course of the maturation.
As scientists fill out the growth curve with new discoveries and data points, they said they hope to answer a variety of outstanding questions about juvenile T. rexes — such as whether or not they experienced a dramatic growth spurt during their teenage years.
“Were juvenile tyrannosaurs ecologically different from adults in aspects other than bite force?” Tseng said.
“What fossilized behavioral evidence can paleontologists bring to bear on this ecological question? Finally, how soon was the predator void filled by other species after the end-Cretaceous mass extinction event that wiped out tyrannosaurs and other non-avian dinosaurs, if those ecological roles remained at all?” Tseng said.