The Ingentia prima – or ‘first giant’ – discovery spurs a rethink on gigantism in dinosaurs.
Research published this week in Nature Ecology & Evolution outlines an early trend towards gigantism in Triassic dinosaurs, centring on the fossil of Ingentia prima.
The Latin name denotes the ‘first giant’ dinosaur, and Ingentia prima is believed to have measured 10 metres long and more than four metres tall, weighing in at about 10 tonnes – the equivalent of two or three elephants.
Ingentia prima is a member of the sauropodomorph family, which includes the largest land animals ever recorded. The early generations were small bipeds and it was thought that giant-size dinosaurs weighing in at more than 10 tonnes arrived with the Jurassic period, which spanned 56m years from the end of the Triassic period.
The origin of gigantism in sauropodomorphs is cited as a pivotal stage in the history of dinosaurs, but the placement of this evolutionary milestone has been obscured by an incomplete fossil record. In the Nature report, researchers from Universidad Nacional de San Juan palaeontology department describe a late Triassic sauropodomorph fossil from Argentina, indicating that the evolution point of gigantism was more than 30m years earlier than previously believed.
“Before this discovery, gigantism was considered to have started during the Jurassic period, about 180m years ago,” said Dr Cecilia Apaldetti, lead author of the study. “But Ingentia prima lived during the last part of the Triassic period, between 210m and 205m years ago.”
The size of Earth’s early inhabitants is important because of what it can tell us about how these long-dead creatures lived and survived. Immense size could have been a defence mechanism for herbivores as the carnivores might not want to take on a colossus for lunch.
The scientists outlined two particular characteristics of the fossil that favoured gigantism. One, a respiratory system similar to that of modern birds and, two, a specific type of bone growth that Dr Ignacio Cerda at the Universidad Nacional de Rio Negro described as “cyclic, seasonal growth”, similar to that of a tree.
Cyclical growth was common in the growth of primitive sauropods in the Triassic period, but these dinosaurs did not typically exceed two or three tonnes. “The interesting thing is that the type of tissue deposited on the bones during these periods of growth is different to that of other sauropods that we know of up ’til now,” said Cerda.