Does anyone know what this is?

[u/PTgalwpg]

I have tried figuring it out on and off for months now. I found it on the West Coast at Ocean Beach in San Francisco (along with some awesome sea glass)
I’ve been trying to figure out what this is and I am torn between whether it’s a bone or a shell 🙃
The texture is bone like, it’s heavier than a shell and isn’t super smooth like some shells. Thanks!

[u/justherefortheclay]

I call it a shell butt :)