The 72-million-year-old herbivore has two large horns above its eyes measuring up to 1.22 metres long. (The University of Utah: Lukas Panzarin)
US palaeontologists say they have unearthed a new species of dinosaurs standing some 1.8 metres tall and weighing up to 4.5 tonnes, with the longest horns of all.
The 72-million-year-old herbivore, now named coahuilaceratops magnacuerna, has two large horns above its eyes measuring up to 1.22 metres long - the largest of any other species, providing fresh insight into the history of western North America.
Scientists uncovered fossils belonging to both an adult and a juvenile of the rhino-sized tubby creature at the Cerro del Pueblo Formation in Coahuila, Mexico.
It measured about 6.7 metres long as an adult.
"We know very little about the dinosaurs of Mexico, and this find increases immeasurably our knowledge of the dinosaurs living in Mexico during the Late Cretaceous," said the study's lead author Mark Loewen, a palaeontologist with the Utah Museum of Natural History.
His team is to release a book next week detailing the find, which took place during expeditions in 2002 and 2003 in the Coahuila desert. The study was funded by the National Geographic Society and the University of Utah.
When dinosaurs lived in this corner of Mexico, it was a lush, humid estuary where ocean water mixed with fresh water from rivers, similar to the US Gulf Coast today.
Many dinosaur bones unearthed in the area are covered with fossilised snails and marine clams, indicating that the creatures lived close to the seashore.
The rocks in which the palaeontologists found coahuilaceratops contained large fossil deposits of jumbled duck-bill dinosaur skeletons.
According to the scientists, the dinosaurs likely died en masse in the area due to storms similar to present-day hurricanes.
During most of the Late Cretaceous Period, 97 to 65 million years ago, high global sea levels led to flooding of the central, low-lying portion of North America.
Ultimately, a warm, shallow sea emerged, stretching from the Gulf of Mexico to the Arctic Ocean and splitting the continent into eastern and western landmasses.
"We are confident that Mexican dinosaurs will be a critical element in unravelling the ancient mystery of this island continent," said Scott Sampson of the Utah Museum of Natural History.