US paleontologists 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.<br/> <br/>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.<br/> <br/>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.