The formation mechanisms of complex BaSO4 fiber bundles and cones in the presence of polyacrylate sodium salt via a bioinspired approach at ambient temperature in an aqueous environment are reported. These complex organic-inorganic hybrid structures assemble after heterogeneous nucleation of amorphous precursor particle aggregates on polar surfaces, and the crystallization area can be patterned. In contrast to earlier reports, three different mechanisms based on the oriented attachment of nanoparticles were revealed for the formation of typical fibrous superstructures depending on the supersaturation or on the number of precursor particles. (A) High supersaturation (S > 2): large amorphous aggregates stick to a polar surface, form fiber bundles after mesoscopic transformation and oriented attachment, and then form a narrow tip through polymer interaction. (B) Low supersaturation (S) 1.02-2): only a few fibers nucleate heterogeneously from a single nucleation spot, and amorphous particles stick to existing fibers, which results in the formation of a fiber bundle. (C) Vanishing supersaturation (S) 1-1.02): nucleation of a fiber bundle from a single nucleation spot with self-limiting repetitive growth as a result of the limited amount of building material. These growth processes are supported by time-resolved optical microscopy in solution, TEM, SEM, and DLS.