it is not possible to pin-point when sea otters began using tools consistently. it is hypothesized that certain behaviors were selected for, in the process of evolution, which led to this adaptation. the first instance of a rock as a tool may have occurred when an otter was unable to access a prey item at the bottom of the ocean and used a rock to facilitate access to the object. similarly, an otter at the surface of the water may have chosen to crush two bivalves against each other when faced with an inability to crush the prey items with the forelimbs or teeth. shellfish are found on rock structures at the bottom of the ocean, so collecting multiple rocks and shellfish from the bottom of the ocean in one diving episode and crushing the objects together on the surface may have led to the association of rocks with crushing shells of foods items. if a behavior which was performed in a conflict situation happened to open a prey item, an otter may have attempted to repeat the behavior and therefore learned to repeat the behavior consistently.