SciTechDaily has a story about Tyrannosaurs rex and how it grew. A new study, published in the journal Proceedings of the Royal Society B, discusses diverse growth strategies in dinosaurs and how that relates to body size. The paper's authors include Tom Cullen of the North Carolina Museum of Natural History and Peter Makovicky of the University of Minnesota, who have both spoken at ESCONI General Meetings.
Tyrannosaurus rex was one of the biggest meat-eating dinosaurs of all time — it measured up to 42 feet long from snout to tail and would have weighed in at around 16,000 pounds. And it wasn’t alone — some of its less-well-known cousins could reach nearly the same size. Scientists have previously shown that T. rex got so big by going through a huge teenage growth spurt, but they didn’t know if that was true for just tyrannosaurs, just them and their close relatives, or perhaps all big bipedal dinosaurs. By cutting into dinosaur bones and analyzing the growth lines, a team of researchers got their answer: T. rex and its closest relatives had an awkward adolescence during which they got huge, while its more distant cousins in the allosauroid group kept on growing a little bit every year.
“We wanted to look at a wide swath of different theropods, two-legged, carnivorous dinosaurs, in order to understand broader patterns of growth and evolution in the group,” says Tom Cullen, the lead author of a new study in Proceedings of the Royal Society B.
Cullen, a scientific affiliate of Chicago’s Field Museum who worked on the study as a postdoctoral researcher at the Field with the museum’s then-curator of dinosaurs, Pete Makovicky, explains, “We particularly wanted to understand how some of them got so big — is the way T. rex grew the only way to do it?”
Makovicky, a scientific affiliate of the Field and professor of geology at the University of Minnesota and the paper’s senior author, says, “We also wanted to see if we got the same growth record when we sampled a variety of different bones from the same skeleton. All these questions about how theropods grew could impact our understanding of the evolution of the group.” Makovicky developed the idea for the project and also discovered several of the dinosaurs whose fossils were analyzed in the study.
The question of how an animal gets big is a surprisingly tricky one. Mammals like us tend to go through a period of extreme growth when we’re young and then stay the same size once we reach adulthood. In other animal groups, that’s not always the case. “Growth rate really varies, there’s no one size fits all,” says Cullen, who is now a postdoctoral researcher at the North Carolina Museum of Natural Sciences. “Birds have super growth spurts and reach adult size really fast, while reptiles like alligators and various lizards and snakes have extended growth. With them, a really, really big individual is probably really old.”
Osteohistological analyses reveal diverse strategies of theropod dinosaur body-size evolution
Abstract
The independent evolution of gigantism among dinosaurs has been a topic of long-standing interest, but it remains unclear if gigantic theropods, the largest bipeds in the fossil record, all achieved massive sizes in the same manner, or through different strategies. We perform multi-element histological analyses on a phylogenetically broad dataset sampled from eight theropod families, with a focus on gigantic tyrannosaurids and carcharodontosaurids, to reconstruct the growth strategies of these lineages and test if particular bones consistently preserve the most complete growth record. We find that in skeletally mature gigantic theropods, weight-bearing bones consistently preserve extensive growth records, whereas non-weight-bearing bones are remodelled and less useful for growth reconstruction, contrary to the pattern observed in smaller theropods and some other dinosaur clades. We find a heterochronic pattern of growth fitting an acceleration model in tyrannosaurids, with allosauroid carcharodontosaurids better fitting a model of hypermorphosis. These divergent growth patterns appear phylogenetically constrained, representing extreme versions of the growth patterns present in smaller coelurosaurs and allosauroids, respectively. This provides the first evidence of a lack of strong mechanistic or physiological constraints on size evolution in the largest bipeds in the fossil record and evidence of one of the longest-living individual dinosaurs ever documented.
