LSAT Logical Reasoning Question of the Day

A paleontologist found a dinosaur tibia and fibula bone group that was too large to be placed into a stabilized storage chest. Luckily, an assistant discovered a way to safely separate the tibia and fibula bones. These bones could be reassembled later without a noticeable change in either bone. Now the bones can be placed in two stabilized storage chests.

The argument above depends on which of the following assumptions?