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.

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.)

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