I was swimming in Sydney Harbour, Australia and I found this bone. I think it could be a tail bone from a fish and would like some help in identifying it if possible. It is 23cm long and 6cm in diameter. I apologise for the previous posts, I was having trouble with uploading a photo. Thank you.

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Tetrapod wizard Darren Naish says: "Mammal scapula, missing most of dorsal end. Looks like cow or similar big artiodactyl."