Phacopidae

Phacopidae is an extinct family of trilobites belonging to the order Phacopida. These marine arthropods were common during the Paleozoic Era, flourishing from the Devonian period until their extinction at the end of the Permian period. Phacopid trilobites are characterized by their large, compound eyes, which were often holochroal, meaning they were composed of many small lenses. Another distinguishing feature is their glabella, the central raised portion of the cephalon (head), which is typically segmented and inflated.

The exoskeleton of phacopids was generally robust. Many species possessed genal spines projecting from the cheeks of their cephalon. Like other trilobites, they underwent ecdysis, shedding their exoskeleton to grow. Their lifestyle varied, with some being bottom-dwellers, while others may have been pelagic or even burrowers. The diversity within Phacopidae is considerable, with numerous genera and species described from fossil sites worldwide. Their widespread distribution and long stratigraphic range make them important index fossils for dating Paleozoic rock formations. The study of phacopids has provided valuable insights into trilobite evolution, paleoecology, and the ancient marine environments they inhabited.