Spinacanthidae is an extinct prehistoric family of tetraodontid bony fish that lived from the Lutetian epoch of Eocene Monte Bolca.

Protobalistum is distinguished from its close, sympatric relative, Spinacanthus, in that its scales are large, and form a sort of armor.

In Spinacanthus, the individual scales are relatively small, and do not touch each other.

Protobalistum and Spinacanthus were a part of the ecosystem of the lagoon that became Monte Bolca.

Because of their similarity to boxfish, and due to their close relation to modern-day triggerfish, spinacanthids may have preyed on shellfish and small fish.