Phacopina

Phacopina is a suborder of trilobites within the order Phacopida. These extinct arthropods are characterized by their distinctive schizochroal eyes, which are composed of separate lenses, each with its own lens element. Phacopina trilobites were a diverse group, exhibiting a range of morphologies and ecological niches.

They are often identified by their inflated glabella (the central lobe of the cephalon or head shield) and prominent eye structures. The schizochroal eye is a defining characteristic, setting them apart from other trilobite groups which typically possessed holochroal eyes. The number, arrangement, and shape of the lenses varied between different genera and species of Phacopina.

Phacopina first appeared in the Ordovician period and persisted through the Devonian period, becoming extinct during the Devonian-Carboniferous extinction event. They are important index fossils used in biostratigraphy, particularly for dating and correlating Ordovician and Devonian rock formations. Fossils of Phacopina have been found worldwide, providing valuable insights into ancient marine ecosystems. Some notable genera within Phacopina include Phacops, Eldredgeops, and Dipleura. The study of Phacopina contributes to our understanding of trilobite evolution, paleontology, and the geological history of the Earth.