Palaeontologists say they have found evidence of a new species here related to the Triceratops, known to have the largest head of any animal ever to have walked the earth.

The new species is slightly smaller at around 23 feet (7 meters) than most Triceratops, but its three-foot-long (0.9 meter) horns were just as big. Holes in its neck frill would also have set it apart.

The scientific name of the new dinosaur will not be revealed until the end of the year, said Scott Sampson, a curator from Utah Museum of Natural History who helped make the discovery with Mexican investigators.

It will be only the second dinosaur species named in Mexico after scientists in February announced a new duck-billed dinosaur from the same region called Velafrons coahuilensis, which cruised the ancient beaches in large herds.

Scientists say they expect to find evidence of dozens of other new dinosaur and plant species buried in Coahuila's rich sediment in coming years.

"This is just the beginning," said Martha Aguillon, a palaeontologist at the local museum near the Rincon Colorado fossil beds in the northern state of Coahuila.

The new three-horned species likely used its massive horns to fight off meat-eating predators.

But scientists say the flamboyant head armour and neck frills were also an important part of courtship rituals, showing dominance with head-butting battles much like modern-day horned animals such as antelope.

"That whole section of the head was for sexual display, it was all ornamentation," said palaeontologist Terry Gates, who works with Sampson at the University of Utah museum and is also one of the scientists behind the Velafrons discovery.

"The females liked it," he added, with a chuckle.

RISING SEA LEVELS

Vegetarian dinosaurs like the new three-horned species and the Velafrons, a much bigger 35 feet (10.7 meters) long, had only their size to protect them from vicious predators like a local cousin of the giant T-rex.

"The Tyrannosaur in Coahuila was a little smaller (than the T-rex) but still nothing you would want to run into in a dark alley," said Sampson. "It was more than 30 feet (9 meters) long and rather intimidating."

The dinosaur discoveries are helping open a window into life in the late Cretaceous Period on the southern tip of western North America.

The continent at the time was sliced in two by a big inland sea stretching from the Arctic Ocean to Mexico's Gulf. The lush, tropical environment provided a perfect habitat for a wide variety of wildlife.

"The land mass these animals lived on was less than one-fifth the size of present-day North America yet we have all of these different elephant-sized animals," said Samson.

Gates said what makes the area in Mexico unique is evidence of sea levels that rose and receded over a period of thousands of years, forcing animals to adapt to new types of environments or pushing some towards extinction.

He said clues from tens of millions of years ago can help scientists understand how nature could react to rising sea levels due to climate changes that are melting polar ice caps.

"We have very little knowledge of the response of land animals to sea level rise," said Gates. "That's exactly why I want to do this study."