Trilobite systematics: the last 75 years

Fortey's order-level review documents that traditional Ptychopariida is a problematic, probably paraphyletic assemblage used in historical trilobite classification. This entity is therefore a historical navigation grade, not a demonstrated clade, ancestor or globally bounded lineage.

Crônier et al. document Siluro-Devonian Phacopidae material and ontogenetic series, while Fortey reviews sampled trilobite systematics; these records are regional and taxon-sampled rather than a complete geographic distribution of Phacopida.

The cited phacopid taxonomy studies focus on morphology, ontogeny and classification, not diet, habitat use, locomotor performance, body size or ecological guild; those fields remain unassigned for Phacopida here.