I am a meat broker, and although that amounts to a hill of beans here. I would have to say, I have no clue. I am not convinced on anything, but idea of a hoof is more aceptable from what I have seen through animal slaughters and "breaking"! Are there any reports of the chemical make-up?, or just the pics?
Sorry to intrude, because there are a lot of brilliant minds already taking a stab, but I would have to say it is a hoof/nail that has not been exposed to much wear and tear. Hence the extra curved point. Think Guiness Books "Longest Nails"
There are 2 PhD and 1 masters students working on fish gut contents for the next few years, and this sort of problem is just a taste of things to come. Classifying animals based on fragmentary remains .... it's an artform.
Myopsida seems supremely confident that this is a bit of fish, John that it's a bit of turtle, and others (like your fine self) that it's an overgrown toenail/hoof. That vascularisation/porosity must be a dead giveaway .... I don't think all the beasts in question would have structure like this; problem is I'm not familiar with horse hoofs, fish lips or turtle bits, so am in no position to comment. Would love to get to the bottom of this, but need access to museum collections to do so ...
I'm in the mammalian nail/claw/hoof camp too. The porous looking structure (subunguis?) does seem to have directional growth lines, unless my eyes are playing tricks with me, which would seem to be consistant with mammalian physiology.
But I could be completely wrong!
Quote on nails fronm the Uni of Colorado:
Mammalian claws are similar to claws of reptiles and birds, embracing and enhancing the tip of each digit. A claw is composed of a harder dorsal plate called the unguis and a softer ventral plate termed the subunguis. The subunguis is continued by the cushion-like pad. Mammals like dogs and cats walk on these pads. In cross-section unguis and subunguis form a U-shaped structure with the unguis enclosing the subunguis. The downward curve is caused by a higher growth rate of the upper surface of the unguis. A claw is thicker in the median line than at the sides. The sides wear more quickly than the center, producing a more or less sharp point. In addition to the protection of the digits, claws are used in many ways for climbing, digging, hanging, or grasping and even killing prey.
Its the shape that has me at a loss, though. If only I had the specimen here I could give a thumbs up/thumbs down on the turtle idea. Hoofs aren't out of the question, but what mammals hang out in that region that have them? Also, is there any indication that this opbject was broken from a cloven hoof, or worn down in any way?