Four skulls of a giant new species of plant-eating dinosaur may give scientists a head start on understanding the biggest animals ever to have walked the Earth, a new study says.

The 105-million-year-old skulls of Abydosaurus mcintoshi were discovered between the late 1990s and 2003 in a sandstone quarry in eastern Utah's Dinosaur National Monument.

Video: Rare Skulls of New Dinosaur Unearthed

Although the site is known as for fossil bonanzas, the newfound skulls are extremely rare, paleontologists say.

That's because the new species—part of a group of ancient four-legged lumberers called sauropods—had long necks capped with tiny, delicate heads, which disintegrated quickly after death.

Since sauropod skulls are so rare, "in my mind I envision herds of these sauropods all with their heads cut off," said study co-author Brooks Britt, a paleontologist at Brigham Young University. "We know so little about their skulls. Now, suddenly, we have four." (Take a dinosaur quiz.)

The recently discovered skulls belonged to young adult dinosaurs, each about 25 feet (8 meters) long, whose skeletons were well preserved because the dinosaurs were quickly entombed by sand and mud. If the animals had lived, they could have reached adult sizes of about 50 feet (15 meters).

It's unknown how the four dinosaurs perished, Britt added. But the animals were probably huddled together in a small valley, possibly near a stream.

The team plans to study each bone of the "mind-boggling" skulls in detail for more clues about the dinosaurs' deaths—"instead of CSI in New York, it's CSI in the mid-Cretaceous," he quipped.

New Dinosaurs Had Dainty Teeth

What's most amazing about the research, Britt noted, is that the Abydosaurus skulls are so similar to skulls of the species' closest relative, the gargantuan Brachiosaurus, which plodded across Earth 45 million years earlier.

But, though the two species' skulls were nearly identical, Abydosaurus had strangely tiny teeth contrasted with its kin: A typical Brachiosaurus tooth is the width of a human thumb, while a tooth from the newfound dinosaur is slimmer than a pinkie finger, generally speaking.

The dainty tooth size is a mystery, but Britt and colleagues have two theories: A lot of wear and tear could have meant that the dinosaurs replaced their teeth often. Replacing smaller teeth takes up less precious body energy.

Likewise, reducing tooth size may have enabled the giants to pack more teeth into their mouths. That would have increased the relative amount of enamel, which was crucial for scraping or biting off plant matter, which sauropods would have then swallowed whole.

Such insights are likely only the beginning of what will be revealed by Abydosaurus, whose Latin name is inspired by the ancient Greek city Abydos, the mythical burial place for the head and neck of Osiris, the Egyptian god of life, death, and fertility.

"With Abydosaurus, we're starting off backward"—working from the head first instead of using other bones, such as backbones, to piece together what the rest of the body would look like, Britt said.

"It gives us a whole new way to look at the dinosaur right out of the blocks."