Anyways, the picture on the previous post seems to have been quite straightforward after all. Yes, it is part of a narwhal tusk, so congrats to all who guessed right! Narwhals, which go by the scientific name Monodon monoceros, are odontocetes (toothed whales), distinguished by the long spiraled tusk seen in the males (and occasionally females) of the species, and are thus sometimes called the "unicorn of the sea".
|Dorsal view of a double-tusked narwhal, on exhibit at the Sant Ocean Hall at the National Museum of Natural History in Washington, DC. Normally, narwhals only have one enlarged tusk (the left one) so this one is an exception.
|Ventral view of the rostrum of extant monodontids.
And here if you or someone you know wants to be a marine biologist.
Muizon, C. de. 1993. Walrus-like feeding adaptation in a new cetacean from the Pliocene of Peru. Nature 365:745–748.
Whitmore, F. C., Jr. 1994. Neogene climatic change and the emergence of the modern whale fauna of the North Atlantic Ocean. Proceedings of the San Diego Society of Natural History 29:223–227.