THOSE TROUBLED TRILOBITES: CLARIFYING EVOLUTIONARY RELATIONSHIPS, DIVERGENCE TIMES AND RATES OF EVOLUTION IN TURBULENT TRILOBITE ORDERS
Here we present phylogenetic analyses using the largest and most comprehensive character matrix to date, which comprises >340 characters, including dependencies and continuous characters. The analyses include 57 exemplar species from all families assigned to either Proetida (sensu Fortey 1997), Aulacopleurida (sensu Adrain 2011), and those previously assigned to Ptychopariida (sensu Fortey 1997) that were excluded from Aulacopleurida. We conducted Bayesian phylogenetic analyses using the fossilized birth-death model to produce trees that would co-estimate topology, divergence times and evolutionary rates. We also assess leaf stability, character influence and stratigraphic fit. We found that the Aulacopleurida forms a non-monophyletic group, and suggest a new taxonomic paradigm incorporating some ‘aulacopleurid’ families back into a monophyletic Proetida with a ptychopariid sister group that has a divergence time in the early Cambrian. Rates of morphological evolution are largely constant through the Cambrian except for some specific taxa with elevated rates, and there is a distinct shift in evolutionary rates around the Cambrian-Ordovician boundary. This wholistic phylogenetic approach provides much needed insight into the evolutionary history of troubled trilobite groups.