Some animals such as western grebes (above) and giant anteaters (below) carry their young piggyback.
Pigs don’t do this so why is it called piggyback?
The term began as two words that morphed into “piggy + back.” Here’s the origin from World Wide Words.
It started out in the sixteenth century as “pick pack,” carrying something on the back or shoulders. Pick is a medieval version of pitch, so it meant a load that was pitched on to a person’s back for carrying. … Piggy-back came along later in the century, with piggyback a modern loss of the hyphen— Origin of piggyback from World Wide Words
At first it was “pick pack.”
Now it’s piggyback.
(photos from Wikimedia Commons; click on the captions to see the originals)