(So it's not exactly a mythical creature, but I couldn't seriously stop picturing the Eighth Doctor with a dinosaur. Have a Double drabble :))
"Comet B/124 !" the Doctor exclaimed as they exited the TARDIS. "Oh you're going to love it, Lucie! A truly peaceful jungle planet- perfect for a holiday. "
"Yeah, heard that before" Lucie remarked. As she trekked through the tall grass, however, something caught her eye. "Doctor, hold on" she began, pointing to a small green creature munching on grass, "Is that a dinosaur?"
The Doctor nodded. "Actually, it's an Ankylosaurus. Name meaning, "great belly."
Lucie watched as the creature came towards them. "Fascinating, I'm sure. But why's it out here? In space? And- Oi!" It licked her hand.
"Greeting you!" the Doctor said, laughing a bit.
----
"Okay, you're barking!" Lucie exclaimed, back at the TARDIS. "There's no way we're keeping that thing."
" Oh I don't know," the Doctor said, patting the dinosaur on the head. "I travelled with a vortisaur for awhile. And she wants to come, don't you Angie?" He asked, his voice in practically a coo.
Oh great, Lucie thought. He's gone and named it!
She sighed, "Oh all right, But I'm warning the both of you," She wagged a finger at Angie and the Doctor. "I'm not cleaning up after her. One mess, and she's straight back here!"