I'm not totally sure those are square nails, but it's hard to tell from your pictures.
At any rate this could have come for just about anything made of wood.
Being found near water a boat is a good guess.
The nails were in the tree when it was still standing and was alive. Each nail has a knot around it. Signs that the tree was trying to protect itself from the damage the nails caused.
The nails were in the tree when it was still standing and was alive. Each nail has a knot around it. Signs that the tree was trying to protect itself from the damage the nails caused.