Just came across this Fusion 360 tutorial in making an articulated hinged dolphin keychain.

https://www.thingiverse.com/thing:2860000

The designer has made a seperate file for the hinge for us to download and reuse.
F360 Hinge model: https://a360.co/2GWWRiM

I tried it out and made a simplied version with a whale tail. It works.