A rare and finely preserved skull unearthed in Argentina belonged to a dinosaur with a drooping head, far bigger eyes and keener hearing than some of its more evolved relatives, providing new clues about this group of lumbering plant-eaters.

The discovery of the skull and part of the neck led paleontologists to announce on Tuesday in the journal PLOS One the naming of a new dinosaur, Sarmientosaurus musacchioi.

The fossil is from a dinosaur that was part of a group known as titanosaurs, and is considered modest in size, about 40 feet long and 10 tons in weight, in contrast to some others in that grouping. “About two elephants’ worth,” estimated Matthew C. Lamanna, an assistant curator at the Carnegie Museum of Natural History in Pittsburgh.

Titanosaurs were plant-eaters with long necks and long tails that could be as small as a cow or as big as a house. While much is known about them, researchers still do not know much about their brains because so few skulls have been found.