Lion

Lions were a type of cat found on Earth (PROSE: Romans Cutaway). Natural prey for lions included zebra (PROSE: Birthright) — though they would certainly attack humans. (TV: The Romans) The Fifth Doctor indicated that, unlike other Terran animals (such as the horse), lions were unique to Earth. (AUDIO: The Bride of Peladon)

Biology
Lions were carnivores. They had canine teeth, which were used for spearing and ripping through meat. Lions used them for catching their prey. They also had incisors, which were used for cutting up food. Their molars were used for grinding up food and their pre-molars were used for chewing food. (WC: Teeth and Eating)

According to the First Doctor, it was the female lions that did the hunting and attacking, while the male lions were lazier, preferring to steal food from another animal than do the chasing themselves. (PROSE: Romans Cutaway)

BC
In 2700 BC, lions inhabited Mesopotamia. The Seventh Doctor and Ace heard one roaring, indicating that one of them had just made a kill. Gilgamesh was fond of hunting lions. (PROSE: Timewyrm: Genesys)

When the Tenth Doctor and June visited Greece in the 16th century BC, they went to the Acropolis, where the Parthenon would later be situated. There, they were attacked by lions. The Doctor defeated one and they both escaped. Later, when they were leaving, they encountered the lions again, which the Doctor subdued by using his sonic screwdriver to tickle the beasts. (PROSE: The Slitheen Excursion)

First millennium AD
Caligula once tried to throw the Doctor to the lions as he did not like the cut of his trousers. (AUDIO: The Labyrinth of Buda Castle)

Ian Chesterton and Barbara Wright were attacked by a lion shortly after arriving in Italy in 64 AD. Ian managed to kill it with a boulder, though he regretted the action. (PROSE: Romans Cutaway) A month later, in July, Ian saw a lion while imprisoned in the city of Rome. It was intended that he fight the beast, but this event was cancelled in favour of a duel for the Roman Emperor Nero. (TV: The Romans)

In about 120 AD, the Tenth Doctor found himself opposing lions, tigers and bears in the Flavian Amphitheatre. However, the lion was easily dispatched with the sonic screwdriver. One burst at the correct frequency immediately sent the cat to sleep. (PROSE: The Stone Rose)

16th century
In 1590, the Moon was home to a species of lion which was invulnerable to weapons made from iron, bronze or stone, but not glass. They were occasionally hunted by the Lunaries. One such hunt was observed by Iris Wildthyme and ambassadors from Earth; the hunt was interrupted by the arrival of a Hydra, which fought and killed the lion. (PROSE: Minions of the Moon)

20th century
On a visit to the Ngorogoro Crater in March 1926, the Seventh Doctor spotted some lions and was reminded of a time when he, perhaps in another incarnation, had seen the last lion on Earth shot in the same area. (PROSE: Prelude Birthright)

In New York City in the 1960s, lions were among the zoo animals released by a mad scientist. (COMIC: The Monsters from the Past) The Third Doctor and Brigadier Lethbridge-Stewart met a lion at a zoo in the 20th century. The lion was as docile as an ordinary house cat. This odd behaviour convinced the Doctor and UNIT to investigate the strange goings-on in the area. (COMIC: The Arkwood Experiments)

In the 20th century, the Fourth Doctor and Sarah Jane Smith went to the London Zoo on the trail of a dying Pescaton. They noted that even the lions were afraid of the shark-like creature. (AUDIO: Doctor Who and the Pescatons)

22nd century
In the 22nd century, the Tenth Doctor again crossed paths with lions, this time at a zoo. After a Dalek invaded the facility, he was momentarily surrounded by lions who had escaped. He escaped the pride only with the help of a vulgle. (COMIC: Carnage Zoo, Flight and Fury)

At some point after the 22nd century Dalek invasion, lions began to live in the forests of England. Men from Becca's village killed and skinned a lion from a forest close to them. (PROSE: Legacy of the Daleks)

Far future
In circa 10,000,000, a lion was one of the animals on board the Ark. (PROSE: The Ark)

Undated events
K9 once encountered lions on a 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, prides of lions lived around acacia trees, males in the branches, females in the shade underneath. (PROSE: K9 and the Missing Planet)

At some point, the Tenth Doctor and Martha Jones encountered lions in the wild in Kenya, whereupon the Doctor falsely advised that they'd be safe because "the lions were more scared of them" than they of the lions. (PROSE: The Pirate Loop)

Alternate realities
In an alternate timeline, lions survived despite the Silurians' reintroduction of extinct species. In Africa, Baryonyx would kill and feed on antelope and leave the scraps for the lions. (PROSE: Blood Heat)

In Pete's World, Mr Crane had "track 90" played once a large-scale cyber-conversion was underway in London. This song referred to sleeping lions. (TV: Rise of the Cybermen)

Cultural references
The Lion, the Witch and the Wardrobe was a book by C. S. Lewis. (COMIC: The Professor, the Queen and the Bookshop)

Nelson's Column, a monument to Horatio Nelson, had four lion statues around it. (TV: The Dalek Invasion of Earth)

Erimem wore a signet ring with the symbol of a female lion. (AUDIO: The Bride of Peladon)

During World War I, there was a Royal Navy ship called the Lion which participated in the Battle of Jutland. Ben Jackson's uncle was one of its crewmembers. (AUDIO: The Mouthless Dead)