Phacopida Trilobites


Phacopida Range Over Geologic TimeSuborder Calymenina is considered to be the earliest and most primitive of the Phacopida, primarily because it has some of the phenotype chracteristics in common with the Ptychopariida. Suborders Calymenina Cheirurina have rostral plates in contrast to suborder Phacopina where the librigena is a single connected piece.

Schizochroal eyes are unique to Suborder Phacopina. While they had fewer lenses (< 700 or so) than the ubuiquitous holochroal eyes, the lenses were larger and each one had its own cornea that extending into a rather large sclera (Treatise, 1997). Schizochroal eyes appear with the Phacopina in the early Ordovician, ostensibly evolved from an ancestor with holochroal eyes (Clarkson, 1975).


Trilobite Order Phacopida

  • Suborder Calymenina
    • Superfamily Calymenoidea
  • Suborder Phacopina
    • Superfamily Phacopoidea
    • Superfamily Dalmanitoidea
    • Superfamily Acastoidea
  • Suborder Cheirurina
    • Superfamily Cheiruroidea

Also see: Phacopida Trilobites Classification

Phacopida Trilobite Fossils