Back in 1997, Argentine paleontologist Rubén D. F. Martínez of the National University of Patagonia found a well-preserved dinosaur skull near the town of Sarmiento. But it wasn’t until recently that Martínez realized he’d discovered a new species of titanosaur, the largest animals to have ever roamed the planet.
Using CT scans, Martínez along with Lawrence M. Witmer, a professor of paleontology at Ohio University and Matt Lamanna, assistant curator at the Carnegie Museum of Natural History in Pittsburgh, determined that the skull and associated neck bones came from an undescribed species of dinosaur, which they named Sarmientosaurus musacchioi and detail in an article published in the journal PLOS One.
The scans revealed that Sarmientosaurus is quite different than other titanosaurs, most of which lived 100 to 95 million years ago during the mid-Cretaceous period, including 70-ton giants like Puertasaurus and Argentinosaurus. Sarmientosaurus is a little smaller, roughly 40 feet long and weighing only 10 tons.
According to Kenneth Chang at The New York Times, the dino had a broad snout and fatter teeth. Large eye sockets suggest that its vision was more advanced than later titanosaurs. Also, its inner ear was tuned to low-frequency sounds. “Maybe to track predators…or the movements of its own herd,” Witmer tells Chang. The position of the inner ear also suggests that Sarmientosaurus kept its head drooped at a 45-degree angle as it foraged on plants.
The scans also suggest the large creature's brain likely was only about the size of a lime. “It’s pretty small,” Witmer tells Chang. “You try not to judge him, but it’s a pretty small brain.”
The skull is special for another reason: according to a press release, despite having identified over 60 species of titanosaur, researchers only have complete or semi-complete skulls for four of them. “Sarmientosaurus has probably the most complete and best preserved skull of any sauropod from South America to date,” paleontologist Mathew Wedel of Western University of Health Sciences in California tells Brian Switek at National Geographic.
Wedel is also a fan of the specimen because it fills in an evolutionary gap in the titanosaurus tree between older species like Brachiosaurus and later relatives. “To me, Sarmientosaurus is cool because it bridges that gap,” Wedel tells Switek. “You can take one look at this thing and say, ‘Yeah, cool, we’ve been waiting for someone like you.’”
Because of the lack of skulls, the mass of detail from the scans is a step forward for paleontologists. “This group, to me, they’re quite mysterious,” Lamanna tells Chang. “By combining data from these different discoveries, we’re gradually building up a picture as to what the biology of these animals was like. In other words, what makes the largest land animals of all time tick?”
For Martínez, the 20-year wait to add his find to the dinosaur family tree has been worth it. “Discoveries like Sarmientosaurus happen once in a lifetime," he says in the press release. “That’s why we studied the fossils so thoroughly, to learn as much about this amazing animal as we could.”