Proceratosauridae is a family of mostly small-bodied tyrannosauroids -- an early branch of the lineage that would eventually produce Tyrannosaurus itself -- known from the Middle Jurassic through Early Cretaceous, roughly 168 to 110 million years ago. The family's hallmark feature is an elaborate cranial crest formed from the nasal bones, paired with unusually enlarged nostrils that in some species exceed a fifth of the skull's total length; crest shape varies widely across genera, from the tall blade-like crest of Guanlong to smaller bumps and ridges in other members. Most proceratosaurids were modest in size, in the range of 2 to 4 meters long, a sharp contrast to the giant tyrannosaurids that would evolve from this lineage tens of millions of years later.
The type genus Proceratosaurus, from the Middle Jurassic of England, was for decades misidentified as an early relative of Ceratosaurus before its true position near the base of Tyrannosauroidea was recognized. Other genera include Guanlong and Kileskus from Jurassic Asia and the much larger, long-crested Yutyrannus from the Early Cretaceous of China, one of the largest feathered dinosaurs known. Because the family sits so close to the root of the tyrannosauroid family tree, it has been central to understanding how the group's later hallmark size and bite force evolved from small, crested, comparatively lightly built ancestors.