A friend showed me this bone. He picked it up in the intertidal zone on a sandy beach on the northern coast of NSW.

I told him I thought it was part of the naturally abraded rib of a Cetacean. Please correct me if I am wrong. I have never handled Cetacean bones.

https://app.box.com/shared/static/qs6n1h2urz9j09bikz0bisbsidjyhymk.jpg

What puzzles me is the taphonomic process that led to the visually odd form of the bone.

In particular, why is the left end forked, with ridges and grooves?

My assumption is that the rib of a Cetacean has longitudinal lines of differing amounts of bone apatite and collagen, leading to differential depth of abrasion.

Is there any literature on this? I would like to know, because some day or other a similar specimen will be handed in as an artefact.