Myfanwy

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

History
Myfanwy was a pteranodon (TW: Meat), which came through the Rift in 2007. (TW: Everything Changes)

It was found hunting in the countryside, killing sheep at night. (TW: Everything Changes) Ianto Jones trapped it in a warehouse and persuaded Jack Harkness to help him catch it. (TW: Fragments) Ianto named it "Myfanwy" after a Welsh goddess who sang beautifully (the pteranodon's screeches sounded 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 used the pteranodon to attack Lisa Hallett, mortally injuring her. (TW: Cyberwoman) The pteranodon 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 in feeding on the burnt corpse. (TWN: Pack Animals)

Personality
Myfanwy came and went from the main base as it pleased, entering through a large opening in the ceiling. Jack Harkness trained it well enough 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 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. Pteranodons were pterosaurs, flying reptiles, while dinosaurs only lived on the land.