An ancestor to the horned dinosaur Triceratops reigned long before its well-known descendant, making it the earliest member of the family, U.S. researchers say.

Paleontologists at Yale University said the new species, dubbed Titanoceratops after the Greek myth of the Titans, rivaled Triceratops in size with an estimated weight of nearly 15,000 pounds and a massive 8-foot-long skull, a university release reported Monday.

Living in the American Southwest about 74 million years ago, Titanoceratops is the earliest known triceratopsin horned dinosaur, suggesting the group evolved into its large size more than 5 million years earlier than previously thought, paleontologist Nicholas Longrich says.

Longrich was searching scientific papers when he saw a description of a partial skeleton of a dinosaur discovered in New Mexico in 1941 which went untouched until 1995 when it was identified incorrectly as Pentaceratops, a species similar to Triceratops common to the area.

"When I looked at the skeleton more closely, I realized it was just too different from the other known Pentaceratops to be a member of the species," Longrich said.

The newly identified Titanoceratops is very similar to Triceratops, but with a longer nose and slightly bigger horns, Longrich says.

Longrich says he hopes paleontologists will find other fossil skeletons that would help confirm the differences between Titanoceratops and its descendants.

"There have got to be more of them out there," Longrich said.