"Torosaurus" is a ceratopsid genus first identified from a pair of skulls in 1891, two years after the identification of "Triceratops". The genus "Torosaurus" resembles "Triceratops" in geological age, distribution, anatomy and size and it has been recognised as a close relative. Its distinguishing features are an elongated skull and the presence of two fenestrae, or holes, in the frill. Paleontologists investigating dinosaur ontogeny (growth and development of individuals over the life span) in the Hell Creek Formation, Montana, US, have recently presented evidence that the two represent a single genus.