Most of the classic creatures that come to mind when you think of dinosaurs are from the Cretaceous period, when evolution seems to have hit its stride and splashed out with things like the huge, long-necked sauropods. But dinosaurs weren't always giants – during the earlier Triassic period they were mostly chicken-sized critters, and they didn't really grow to be massive until the Jurassic. Now, the discovery of a new species in Argentina is pushing back the clock on dinosaur gigantism by up to 30 million years.
The creature has been dubbed "Ingentia prima" (Latin for "first giant"), and it's been classed as a sauropodomorph, the group that would later evolve into the gigantic sauropods. Although it has a much shorter neck and more theropod-like feet, the family resemblance is clear. Ingentia has been estimated to have weighed about 10 tons, which is huge for its time but makes it a relative lightweight next to some of its descendants like Patagotitan, the largest land animal to ever walk the Earth.
"Before this discovery, gigantism was considered to have arisen during the Jurassic period, about 180 million years ago, but Ingentia prima lived at the end of the Triassic, between 210 and 205 million years ago," says Cecilia Apaldetti, lead author of a study describing the new find. "It is a true giant, especially for that moment of evolution where most of the animals that coexisted did not exceed two meters in height and the largest reached, at most, three tons.
"That is why we see in Ingentia prima the origin of gigantism, the first steps so that, more than 100 million years later, sauropods of up to 70 tons will come into being, as Argentinosaurus or Patagotitan, from southern Argentina."
The team also found biological evidence for just how the creature managed to get so big so early. Ingentia seems to have had a respiratory system much like that of modern birds: in addition to lungs, it had a pair of air sacs that would allow it to have a reserve of oxygenated air and let it cool down faster.
"Ingentia had pneumatic cavities in its bones, which indicates the presence of highly developed air sacs, a very efficient breathing system such as that of current birds, and that consequently lightened his weight," says Oscar Alcober, co-author of the study.
On top of that, Ingentia also seems to have grown in seasonal spurts kind of like a tree, instead of steadily like most other animals. Based on this unusual growth pattern, the researchers have classed Ingentia into a new family called Lessemsauridae, which includes a few other previously-disparate members.
The research was published in the journal Nature Ecology & Evolution.
Source: National University of San Juan
