A previously undiscovered species of dinosaur was unearthed by palaeontologists who made a rare find of four skulls.
Abydosaurus was a type of sauropod, a group of huge plant-eating dinosaurs - including Brachiosaurus - which had light skulls because the head was at the end of a long neck.
Complete skulls were recovered for only eight of more than 120 types of sauropod so researchers were shocked and thrilled when they found four Abydosaurus skulls - including two intact - at a quarry in the Dinosaur National Monument in eastern Utah, US.
Dr Brooks Britt, a palaeontologist at Brigham Young University who worked on the project, said: "Their heads are built lighter than mammal skulls because they sit way out at the end of very long necks.
"Instead of thick bones fused together, sauropod skulls are made of thin bones bound together by soft tissue. Usually it falls apart quickly after death and disintegrates."
Most of what scientists know about sauropods is from the neck down but the newly discovered skulls provided a few clues about how the largest land animals to roam the Earth ate their food.
Dr Britt said: "They didn't chew their food; they just grabbed it and swallowed it.
"The skulls are only one two-hundredth of total body volume and don't have an elaborate chewing system."
Dr Britt said Abydosaurus is thought to have lived 105 million years ago as crystals of the mineral zircon within the surrounding rock have been dated to that period.
Bone analysis suggests Brachiosaurus, which grew to around 25 metres long and lived 45 million years earlier than Abydosaurus, is thought to have been its closest relative.