Myfanwy

Myfanwy was a pteranodon kept by Torchwood Three as a pet.

History
Myfanwy was a pteranodon, possibly from either Cretaceous Earth or an alternate Earth where its kind never became extinct. (TW: Meat) It came through the Rift in 2007. (TW: Everything Changes)

It was originally found hunting in the countryside, killing sheep at night. (TW: Everything Changes) Eventually, Ianto Jones was able to trap it in a warehouse and persuaded Jack Harkness to help him catch it. (TW: Fragments) Ianto named it "Myfanwy" after a Welsh goddess with beautiful singing (ironically, as the pteranodon's screeches sound horrible). (WEB: torchwood.org.uk)

It became Torchwood Three's mascot and pet, and an essential part of their everyday life, even taking part in a basketball game (TW: Cyberwoman)

Jack Harkness was later able to use the pteronodon to attack Lisa Hallett, mortally injuring her. (TW: Cyberwoman) The pteronodon, on the other hand, survived the encounter. (TW: Meat)

When an Apatosaurus-like alien was accidentally brought into the Torchwood hub, Myfanwy tried to fight it, allowing Toshiko Sato to get to the armoury. After it was destroyed by a Jamolean lance, Myfanwy seemed to take pleasure on feeding on the burnt corpse. (TWN: Pack Animals)

It is unknown if Myfanwy survived the destruction of Torchwood Three. (TW: Children of Earth: Day One) However, it is possible, as Myfanwy had been allowed out of the Hub into the open at times, so it may not have been present during the Hub's destruction. (TW: Everything Changes)

Personality
Myfanwy came and went from the main base as it pleased, entering through a large opening on the ceiling. Jack Harkness trained it well enough so that it it returned to the base on hearing a signal from his wristwatch, it never attacked a member of staff, never made a mess and only ate food treated with a certain "barbecue sauce", which Suzie Costello had developed. (WEB: torchwood.org.uk, TW: Cyberwoman, TWN: Pack Animals) The pteranodon also had a fondness for dark chocolate, (TW: Fragments) cod, (WEB: torchwood.org.uk) and would also feed on birds which perched around Torchwood Three (TWN: Another Life).

Behind the scenes

 * Torchwood Declassified mentions that the pteranodon was nicknamed "Myfanwy" by the cast. This is later shown to be the case in-universe, when the Torchwood site featured an IM conversation between Ianto and Owen about Myfanwy's feeding habits. (WEB: torchwood.org.uk)
 * Jack refers to the beast as a dinosaur but it is not as Pteranodons were pterosaurs, flying reptiles, while dinosaurs only lived on the land.