Well, the chick grew up into a chicken, but you’re still not sure how the egg got into that cave...

Piko was born into the company of dragons- oddly enough.  In fact, she initially thought that she was a dragon herself.  Soon, though, she realized she was different from the golden wyverns who raised her from birth.  And when the dragons her age began to grow up and tease her for being different, she left the family to find out if there were any other creatures like her.  She found one: a chick who she named Piyo Piyo after the sounds it made.  They both returned to the mountain-cave to show the other dragons.  But the other chick did not seem to age as she had.  It was quite confusing for Piko, not knowing where she was from.  But, being quite lighthearted and unaccustomed to thinking seriously, she didn't really care.