Triceratops

The Triceratops were a type of herbivorous dinosaur on prehistoric Earth.

History
Triceratops had two large horns at the top of their heads and one small one near their nose. They weighed over a ton and could be very dangerous in a fight. They had a frill made of solid bone above their heads and ate with a beak.

The Third Doctor encountered a few that had been transported to the 1970s. (TV: Invasion of the Dinosaurs)

In an alternate universe Triceratops were one of the creatures bought back from extinction by the silurians and were allowed to roam free (PROSE: Blood Heat)

The Eighth Doctor and Samantha Jones once returned a baby triceratops to its mother. (PROSE: Unnatural History)

The Triceratops was worth 550 points in the I-Spyder Book of Earth Creatures. (PROSE: The Last Dodo)

Triceratops was among the species placed aboard the Silurian Ark to repopulate the Earth with after the catastrophe the Silurians incorrectly predicted had passed. In the 24th century, when the Eleventh Doctor and his companions came aboard the Ark, they used a Triceratops, nicknamed Tricey as a mount. Solomon later had the Triceratops killed to make an example out of it.

It is unknown whether there were any other Triceratops aboard the Ark at the time, but if there were then they were presumably moved by the Doctor to the planet Siluria with the other dinosaur specimens. (TV: Dinosaurs on a Spaceship)

Similar creatures
The planet Skaro was also home to creatures that resembled dinosaurs, specifically the Triceratops, but with only one horn. Normally peaceful herbivores, they would attack Daleks on sight. The Third Doctor and Finney used a herd of these to destroy a group of Daleks that had taken them to Skaro. (COMIC: The Planet of the Daleks)

Behind the scenes
According to non-narrative material in DWBIT 7, the Triceratops was also native to the planet Raxas, and along with the other Raxas dinosaurs, proved to be more than a match for a Dalek attack.