After years of digging and research, paleontologists have identified a new species of dinosaur – and it seems to be the largest land animal to ever walk the Earth. Over 150 bones from at least six individual animals were found in a dig site in Argentina, and from those scientists were able to estimate their body mass, age, and the environment the beasts came from.
As the name suggests, the family group titanosaur contains some of the biggest known dinosaurs, and the newest addition is the largest yet. Dubbed Patagotitan mayorum, the first part of its name means "giant from Patagonia," while the second bit honors the Mayo family, who owns the ranch where the fossils were discovered in 2012.
Excavating the site was a three-year project, as the team pieced together at least six different animals, all young adults, from over 150 fossils, spread across three layers of rock. Then, it took a further two years of preparation and research in the lab of the Museum of Paleontology Egidio Feruglio before it could be declared a brand new species and named.
"When we discover a new dinosaur in the field, it does not mean that we baptize it as soon as we return to the museum; this is a process that takes a lot of work," says José Luis Carballido, lead author of the study. "We compared the remains with all the species that could be related to Patagotitan, not only in terms of size but also also those that lived at the same time or had certain features in common. Among them we included species such as Argentinosaurus, Puertasaurus and Futalognkosaurus, which are other giant species of dinosaurs from Argentina. We performed a detailed comparison against all these species and found some striking differences."
Since the creatures' most notable feature is its size, the scientists used several techniques to estimate its body mass. The first calculations were made based on the circumference of its leg bones, which can reveal how much weight they needed to support. The second strategy involved trying to reconstruct the animal as it may have been in life, to determine the volume and density of the tissue that once surrounded the bone.
"To achieve this, a tridimensional reconstruction of Patagotitan was made," says Carballido. "In the first place, a scanning of each fossil had to be performed. Later on, a reconstruction of what its possible soft tissue volume would be like was added to be able to calculate its weight by comparing it to living animal's density."
This technique was made possible thanks to the relatively complete skeletons found, allowing the team to estimate the Patagotitan's average weight to be about 70 tons. That makes it one of the largest land animals to ever exist, although it's still dwarfed by the largest animal of all time – the blue whale – which can tip the scales at up to 200 tons.
Comparing the new species to existing relatives, the paleontologists were able to determine its place in the family tree, helping them understand the evolutionary history of the creature. According to their findings, all of the titanosaur species in Patagonia belonged to a single lineage.
"This means that the evolution of extreme gigantism within titanosaurs happened but only once, and not in multiple separate events," says Diego Pol, co-author of the study. "We can see some other cases of size increase relative to the ancestral size of titanosaurs, but none of them was as dramatic as the one seen in this group and exemplified by Patagotitan. This means that apparently almost all the truly giant dinosaurs were related to each other and form the group known as Lognkosauria."
The crowded dig site also allowed the researchers to piece together the environment of the area as it would have been during the mid-Cretaceous period, some 100 million years ago, and the social lives of the titanosaurs that frequented the spot.
"The environment in which those bones were deposited and buried was a floodplain, where successive river overflows had covered the dead animals' remains," says Carballido. "These overflow's energy wasn't strong enough as to move the bones. In other words, these dinosaurs were there, died there and had gone to that place in at least three different occasions. In one of the levels there is a femur that, clearly, had been stepped on by another animal. At present, this is something common in places where elephants come back frequently, for example. It is very normal that they step on another elephant that was dead before."
The research describing Patagotitan mayorum was published in the journal Proceedings of the Royal Society B, and a 122-ft (37-m) long replica skeleton is currently on display at the American Natural History Museum in New York.
