The Arachnomorpha or Arachnata concepts have resolved Trilobita as most closely related to Chelicerata amongst extant Arthropoda. An alternative position of trilobites in the stem lineage of Mandibulata is suggested by their pattern of head tagmosis. The antennae of trilobites and Mandibulata are considered non-homologous with the antennae of Onychophora and stem lineage Euarthropoda: they repr...

Correlation of Lower Cambrian rocks is hampered because there are no widespread and rapidly evolving organisms such as the later agnostids, graptolites, conodonts, ammonites, or planktonic foramini fers, that might provide basis for a consistent intercontinental biostratigraphy. Four problems illustrate issue: 1) age oldest trilobites China; 2) acritarch correlations between Siberia Baltica; 3)...