"As soon as we found it, we realised it was something different".
The team also found biological evidence for just how the creature managed to get so big so early.
Ten-dinosaur weighing about ten tons was named Ingentia prima - "first giant".
Recently-unearthed fossils in Argentina suggest that giant dinosaurs roamed the Earth some 30 million years earlier than scientists had previously thought. "It was at least twice as large as the other herbivores of the time".
Ingentia prima was a four-legged herbivore which lived about 47 million years before diplodocus.
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 huge sauropods. However, Ingentia prima inhabited the Earth in the late Triassic period, somewhere between 210 and 205 million years ago.
She and her team discovered the remains in the San Juan province in 2015.
Sauropods are the largest known creatures to ever walk on land but these massive dinosaurs did not emerge with their bodies already bulked up. As for the bones, they belonged to the neck, tail, front and back legs. "That's the surprise", asserted Cecilia Apaldetti, a San Juan University researcher.
The researchers found that the weight of I. prima ranged between seven and 10 tons, and showed elongated neck and long tail albeit not as pronounced as those seen in their later relatives.
Large size, scientists believe they began to be achieved only in the middle and at the end of the Jurassic period, about 180-155 million years ago, when the first neosauropods, including Diplodocus, argentinosaurus and all of the largest dinosaurs of that era. Cyclic growth was common in the dinosaurs of that period, but they usually stopped growing until they reached nearly 1.8 tons in weight and 3 meters in length.
While later giant dinosaurs grew in an accelerated yet continuous manner, an examination of its bones showed that Ingentia grew seasonally rather than continuously, but at an even higher rate.
"These pneumatic cavities indicate that this new species had highly developed air sacs and a very efficient breathing system, similar to what happens in modern birds, which also helped it to keep its body cool despite its large size", said Apaldetti.
The last, iconic sauropods had the benefit of a long history of evolutionary innovation in this regard, said Dr Apaldetti.