Unusual dagger, billfish or bone “blade”?

[Ian]

Hi David,

The baculum bone is an interesting structure that shows a high degree of variation in length and shape among the various mammal groups that have one. In several species, the baculum is actually a Y-shaped structure with two separate arms that unite into a singe longer bone. In others, the two arms may still be present but they appear fused together, as a widening at the proximal end of the bone. Basically the two arms fuse into a single bone. The two arms each have a medullary cavity (for bone marrow) and fuse to form a single such cavity more distally. Thus, the proximal end in cross section shows two central cavities. This is what drew me initially to think of a baculum for the example in the original post. Because the tissue in the canals is missing in the cavities shown in the OP, we don't know what may have been there, There is the suggestion of a membrane that may have lined the cavity, but not enough evidence to distinguish a "nerve cavity" from a "medullary cavity" in a long bone (at least as I look at it).

As far as straightness, some species (including the walrus) can have straight baculum. Attached is a picture of a walrus baculum that resides in the Medical Museum of the University of Melbourne not far from where I live now.

As I noted in my original comment, if this is a baculum, it is an uncommonly large and straight one, and would have had some carving done to produce an acute point. Then again it could be the bill of a swordfish.

Whether a walrus baculum or the rostrum of a swordfish, there is a nautical flavor to the item and I would opt for maritime SE Asia as its origin.
.