"It makes sense to envision Sarmientosaurus standing with its feet planted and moving that long neck around like the wand of a vacuum cleaner while the head vacuums up all the low-growing plants in the area," study author Lawrence Witmer of Ohio University told Reuters. The presumed posture of the 95-million-year-old Argentinian dinosaur was revealed by the orientation of its inner ear.
That inner ear info makes Sarmientosaurus musacchioi pretty special. Titanosaurs are the biggest creatures ever known to walk on land, and they were once pretty common. But their heads are shockingly hard to come by.
"When you've got a river system, or any kind of environment where the water is moving quickly enough to transport enough sediment to bury one of these behemoths in time for it to be relatively well preserved, oftentimes, currents of that magnitude are probably going to wash away pretty small and delicate structures, such as heads," study author Matthew Lamanna of the Carnegie Museum of Natural History told Live Science.
As a result, titanosaur skulls are some of the rarest kinds of dinosaur fossils. Sarmientosaurus is only the fourth titanosaur to come with a fairly complete skull to study — out of over 60 named species.
Its precious skull offered up more than just hints at a droopy head: Like other known sauropods, musacchioi's brain was downright puny relative to the size of its body. The creature was 50 feet long and weighed around 12 tons (the weight of three or four female elephants), but had a brain the size of a lime.
"Sarmientosaurus, bless its heart, was not the sharpest tooth in the jaw," Witmer told Reuters.
But the dinosaur also had relatively large eye sockets, according to the researchers — which could mean that it had better eyesight than other titanosaurs, at least in theory. The researchers also believe that the dinosaur's inner ear was well suited for picking up low frequencies, suggesting that it may have used low, rumbling calls to communicate with its own kind.
The skull also reveals facial structures associated with more primitive dinosaurs — the older sauropods that titanosaurs descended from. It helps fill in the fossil record of its family tree, indicating that some of the headless titanosaurs out there may have retained the looks of their ancestors even as others evolved in different directions.
“To me, Sarmientosaurus is cool because it bridges that gap,” paleontologist Mathew Wedel of Western University of Health Sciences, who wasn't involved in the study, told National Geographic. “You can take one look at this thing and say, ‘Yeah, cool, we’ve been waiting for someone like you.’"