Mammoth

Mammoths were a species native to Earth in prehistory. Though remembered by humans merely as large, lumbering beasts, they possessed great power and intelligence in the time before time and their leader Cernunnos would later become a great threat to the Great Houses themselves.

Prehistory
In the Dark Times before the Time Lords created history, there existed cities carved into gigantic ivory tusks where scholars and philosophers rode on the backs of steam-powered mammoth skeletons. (PROSE: Christmas on a Rational Planet) The mammoths ruled these cities and were in turn ruled by Cernunnos. The mammoths created stone men and then used breeding-engines to create humanity.

After the creation of the Spiral Politic, Cernunnos ordered the humans to hunt mammoths to extinction. A trace of loyalty to mammoths remained in humanity's collective memory for billions of years. The ruins of one of the mammoths' ivory cities stayed hidden in an alter-time realm. (PROSE: Cobweb and Ivory)

Around 100,000 BC, Martha Jones watched herds of mammoths while the Tenth Doctor went to retrieve the bodies of Modrikanians who had died in a crash on Earth. (PROSE: Snowglobe 7)

Nimrod's Neanderthal tribe herded mammoths "sunward to find new grazing." (TV: Ghost Light) According to the Fourth Doctor, the Neanderthals could knock up a good Mammoth casserole. (PROSE: The Romance of Crime)

While being pursued by the Trods through time, the Second Doctor visited prehistoric Earth, where he used his recorder to befriend a herd of mammoths and get them to destroy the Trods' power supply. (COMIC: Pursued by the Trods)

The Ninth Doctor and Rose Tyler on a visit to prehistoric Earth encountered a mammoth killed by a Hy-Bractor. (PROSE: Only Human)

After being flung back in time by a Time Cube, the Fourth Doctor, Sarah Jane Smith and Dr. Bhoul encountered a caveman and a raging mammoth. (PROSE: The Time Snatch)

Circa 35,000 years ago, the Eleventh Doctor and Rory Williams visited the future site of Los Angeles, California, where the TARDIS became stuck in a tar pit. A mammoth was also stuck in the tar pit with them. (COMIC: The Doctor and the Nurse)

There was a picture of a mammoth in Malohkeh's database. (TV: Cold Blood)

Modern times
In 1774, King George III of the United Kingdom received a weakened Cerunnos as a gift from Catherine II of Russia. (PROSE: The Adventuress of Henrietta Street, Cobweb and Ivory, Grass, COMIC: Political Animals) As late as 1804, Thomas Jefferson believed that woolly mammoths still roamed the North American midwest and even sent an expedition to find one. An woman named Lucia Cailloux killed all the North American mammoths to prevent him from finding them. (PROSE: Grass, The Adventuress of Henrietta Street)

In 1894, a spaceship containing temporal radiation exploded near the London Zoo, devolving one of its elephants to a mammoth. (PROSE: The Evolution Episode)

When Professor Grisenko discovered Skaldak encased in ice in 1983, he thought that he was a mammoth. (TV: Cold War)

In 2010, woolly mammoths were some of the prehistoric creatures brought into Sydney by chronal waves caused by the SKARDIS. (COMIC: The Age of Ice) In the same year, the Eleventh Doctor and Amy Pond encountered an alien spaceship disguised as a mammoth in New York City. (PROSE: The Forgotten Army)

In the posthuman era, Cernunnos was resurrected at Terra Primagenia. Returning to the remains of the pre-Anchoring mammoth empire with the unwitting help of Avus, Cernunnos began planning to undo the anchoring of the thread in a War against the Great Houses. (PROSE: Cobweb and Ivory)

Alternate timelines
In an alternate timeline, the Silurians brought back the mammoths, raising them for food and allowing them to roam the mountains of Earth. (PROSE: Blood Heat)

In another alternate timeline, an American news anchor told her audience that the Holy Roman Emperor Winston Churchill had a "personal mammoth", and that he returned to the Buckingham Senate atop it. (TV: The Wedding of River Song)

Other planets
A zoo on an Earth-like planet exhibited a mammoth or a mammoth-like creature. (COMIC: The Didus Expedition)

The Junlangis of Dellah were white, mammoth-like creatures. (PROSE: Twilight of the Gods) Yahoomer's species resembled orange mammoths with four trunks. (PROSE: The Monsters Inside)

K9 once encountered some mammoths on an unnamed planet in another dimension, partially inhabited by ex-Tellac miners. They lived alongside other Earth animals from widely varying periods of evolutionary history. On this planet, he observed a mammoth fighting a sabre-toothed tiger. (PROSE: K9 and the Missing Planet)

Due to a fracture in time caused by the Last Great Time War, mammoths on Traxis coexisted with dinosaurs, neanderthals, and robots. (COMIC: Weapons of Past Destruction)