Vortisaur

Vortisaurs were pterodactyl-like creatures who lived in the Vortex.

Biology
The Doctor described vortisaurs as birds of prey. 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 are fixed with sharp teeth; on biting, beyond the physical wound, the chronal energies of the creature age the wound and the surrounding tissue by decades. (BFA: Storm Warning)

Individual Vortisaurs
The Doctor encountered a flock of Vortisaurs scavenging from the hulk of a time ship; his efforts to drive them off, only resulted in his being attacked himself. Although he managed to retreat to 1930 France, 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 rid it to escape the crash of the airship. Charley takes a liking to the Vortisaur, naming it Ramsey after the Prime Minister of her time, James Ramsay MacDonald. (BFA: Storm Warning) After a number of failed domestication attempts, Ramsay is eventually released back into the Vortex. (BFA: Minuet in Hell)

The Doctor also encountered Vortisaurs ridden by marauding time warriors; again showing his affinity for the species, the Doctor at one point mounts one of these Vortisaurs, quickly giving it the name "Margaret, presumably after Margaret Thatcher. (BBCR/BFA: No More Lies)

Other information
The Doctor appeared to have training in the handling of Vortisaurs. He referred to them as "bloodhounds" and showing a proficiency for handling of the beasts. On at least two occasions he offered anecdotes of his days as a youth, riding Vortisaurs bareback. (source?)