Vortisaur

Vortisaurs, or Pterosauria vortexfera, (AUDIO: Storm Warning) were pterodactyl-like creatures which lived in the Time Vortex.

Biology
The Eighth Doctor described Vortisaurs as "extradimensional bird[s] of prey". (AUDIO: Storm Warning) They were large enough to support a human-sized creature. (AUDIO: Storm Warning, No More Lies)

In the vortex, Vortisaurs were drawn to the chronal distortions radiated by objects passing through. They would occasionally scavenge from ships wrecked and lost there. Their jaws were fixed with sharp teeth; on biting, beyond the physical wound, the chronal energies of the creature aged the wound and the surrounding tissue by decades. (AUDIO: Storm Warning)

Their skin was indigo with stripes. (AUDIO: The Book of Kells)

History
The Vortisaurs were known to the Time Lords. In his youth, the First Doctor had ridden them bareback while at the Academy on Gallifrey and was proficient in handling them. (AUDIO: Storm Warning)

Fitz Kreiner once compared them to Vortex Wraiths, calling them more common and less chaotic inhabitants of the vortex. (PROSE: The Slow Empire) The Eighth Doctor encountered a flock of Vortisaurs scavenging from the hulk of a time ship; his efforts to drive them off only resulted in him being attacked himself. Although he managed to retreat to France on 5 October 1930, materialising his TARDIS on board the airship R101, he unknowingly towed one of the creatures along with him, a fact revealed when it began to attack the airship crew. The Doctor and his new companion Charley Pollard then rode it to escape the crash of the airship. Charley took a liking to the Vortisaur, naming it Ramsey after the Prime Minister of her time, Ramsay MacDonald. (AUDIO: Storm Warning) After a number of failed domestication attempts, Ramsay was eventually released back into the Vortex. (AUDIO: Minuet in Hell)

The Eighth Doctor also encountered Vortisaurs ridden by Tar Modowk. He rode one of these Vortisaurs, naming it "Margaret." (AUDIO: No More Lies)

When the Meddling Monk used a time scoop in an attempt to drag the Doctor's TARDIS to Ireland in 1066, he accidentally pulled a Vortisaur out of the Time Vortex. Shortly before its death, the Vortisaur immolated Brother Timothy, one of the monks at the Abbey of Kells. The other monks used the Vortisaur's hyde to make vellum. (AUDIO: The Book of Kells)