The design takes inspiration from the interlocking suture patterns found on the fossilized shells of ammonites, an extinct relative of the octopus that roamed the ancient oceans. Sutures are complex, fractal boundaries that separate the chambers of an ammonite's shell. Though their true origin is unknown, we used a simulation of dendritic solidification to make suture-like patterns. Branching structures emerge during supercooled crystal growth due to the interplay of phase change and temperature as liquid becomes solid. The result are fluid, branching forms where positive and negative shapes interpenetrate to form a complex boundary.