Artiopoda

Artiopoda is a clade of extinct arthropods within Euarthropoda that includes the well-known trilobites and a number of closely related, now extinct lineages. The group is defined mainly through phylogenetic analyses that seek to reconstruct relationships among early arthropods, rather than by a single diagnostic character. Artiopods are primarily known from the fossil record and span a wide range of Middle Cambrian to late Paleozoic rocks.

Anatomy within Artiopoda is diverse, but many members share a generally compact body plan with a head region (cephalon) and a segmented trunk. Trilobites, the most familiar artiopods, typically possess a calcified exoskeleton, a distinct cephalon and pygidium, and an axial lobe with lateral pleural regions. Some artiopod groups show enrollment or other defensive postures, and limb morphology varies across lineages, reflecting ecological diversification.

The fossil record of Artiopoda is global and spans major Paleozoic intervals, with trilobites being especially abundant and long-lasting in the early Paleozoic seas. Artiopod fossils have contributed significantly to understandings of early euarthropod evolution, including the development of segmentation, exoskeletal types, and the transition from soft-bodied to more heavily sclerotized forms in this segment of arthropod history. While trilobites dominate popular depictions, artiopodan diversity showcases a broader spectrum of ecological roles in ancient marine ecosystems.