Trilobite Systematics

Phylogenetics is the study of evolutionary relationships (progenitors, descendents, and evolutionary branching) among groups of organisms. The relationships are hypothesized through morphological data for fossils, and with molecular phylogenetics using nucleotide sequences encoding genes or amino acid sequences encoding proteins for extant organisms. Obviously, sequencing of trilobite genes and proteins is impossible, and so trilobite phylogenetics is largely based on cladistics,an approach to biological classification where organisms are grouped together based on whether or not they share morphological traits (particularly unique characteristics) derived from the group's last common ancestor, and that are not present in more distant ancestors. The process results in an evolutionary taxonomy that shows ancestral progenitors and descendants in a tree-like structure.

Taxonomy and Phylogeny within Class Trilobita

The taxonomy and basic phylogeny of Class Trilobita are shown below that are mostly consistent with the 1997 Treatise on Invertebrate Paleontology, Part O (Trilobita) and Richard Fortey's important 2001 work summarizing 75 years of trilobite systematics, where Fortey laments that despite "complex morphology and a long geological
history with an apparently good fossil record, their systematics is still in an unsatisfactory state".