Ingentia prima shows that gigantism in dinosaurs already began in the Triassic period

Ingentia prima
Ingentia prima

An article published in the journal “Nature Ecology & Evolution” describes the discovery of a sauropod dinosaur, a herbivore of the long-necked type dating back to the Late Triassic period. Named Ingentia prima by the team led by Dr. Cecilia Apaldetti of the Instituto y Museo de Ciencias Naturales in San Juan, Argentina, it was a giant herbivore that lived in today’s South America about 205 million years ago, 25 million earlier than thought.

Giant dinosaurs and in particular the enormous herbivores of the suborder Sauropodomorpha are typical from the Jurassic period or so it was believed. Already in 1999 in the Los Colorados Formation of today’s province of La Rioja, Argentina, fossils of Lessemsaurus sauropoides, a 9-meter long sauropod, dating back to the Late Triassic period, were discovered. Now a new search in a nearby location and precisely at the site of Balde de Leyes, in the province of San Juan, discovered another sauropod from the same period that could be even bigger.

Dinosaurs appeared in the Triassic period and slowly paleontologists are finding evidence that the gigantism of some groups wasn’t a phenomenon of the Jurassic but emerged already towards the end of the Triassic. Long between 7 and 10 meters for a weight that could reach 10 tons, Ingentia prima was already a giant about 205 million years ago.

Two partial skeletons of Ingentia prima were recovered and show a relationship with Lessemsaurus sauropoides. For this reason, the researchers created a clade called Lessemsauridae that includes those two species together with Antetonitrus ingenipes, another sauropod that emerged a little later, at the beginning of the Jurassic period.

According to the researchers, the rate of bone accumulation in Ingentia prima was greater than the species of its period and the largest giants that lived in today’s Patagonia, in southern Argentina. Its bone fragments show a cyclical and seasonal growth different from other sauropods that allowed it to grow rapidly.

Another reason for interest in the bones of Agentia prima is in their cavities, which made them lighter, favoring a greater body size. Those cavities indicate that this species had already well developed air pockets and a very efficient respiratory system that already had similarities with modern birds.

The two images (courtesy Jorge A. González, all rights reserved) show reconstructions of Agentia prima. The top one shows its hollow bones and the respiratory system with the air pockets in green. A reconstruction of this dinosaur’s general appearance can be seen in the bottom image.

In essence, the discovery of Ingentia prima’s fossils is really interesting because it shows the evolution of some characteristics typical of titanosaurs already in the Triassic period. In the Jurassic, thanks also to the evolution of further anatomical traits, other iconic species became the giants we’ve known for a long time.

Ingentia prima
Ingentia prima

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