This creature is based only a one photo of beluga-skeleton and from there you can see only some parts of spine and jaws. Rest are just creature's creator own imagination. *Forms a rainbow with hands*
A great pic of one of the classic SCPs.
Also apparently Butch Hartman used this image as a reference for what 682 actually looks like after he tried drawing a couple just going by the description he was given in a video he posted about two weeks ago.