The distribution of all known Cambrian echinoderm taxa, encompassing both articulated specimens and taxonomically diagnostic isolated ossicles, is documented for the first time. The database described by 2011 comprises 188 species recorded from 65 formations from around the world. Formations that have yielded articulated echinoderms are unequally distributed in space and time. Only Laurentia and West Gondwana provide reasonably complete records at the resolution of Stage. The review of the biogeographical distributions of the eight major echinoderm clades shows that faunas from Laurentia and Northeast Gondwana (China and Korea) are distinct from those of West Gondwana and Southeast Gondwana (Australia); other regions are too poorly sampled to make firm palaeobiogeographical statements. Analysis of alpha diversity (species per formation) shows that diversity rose initially to Cambrian Stage 5, declined into Guzhangian and Paibian before returning to Stage 5 levels by the end of the Cambrian. This pattern is replicated in Laurentia and West Gondwana. We show that taxonomically diagnostic ossicles found in isolation typically occur significantly earlier than the first articulated specimens of the same taxa and provide important information on the first occurrence and palaeobiogeographical distribution of key taxa, and of the phylum as a whole.Supplementary material:Articulated Cambrian echinoderms and Isolated plates of Cambrian echinoderms are provided at:http://www.geolsoc.org.uk/SUP18668

The phylogenetic relationships between major groups of plesiomorphic pentaradial echinoderms, the Paleozoic crinoids, blastozoans, and edrioasteroids, are poorly understood because of a lack of widely recognized homologies. Here, we present newly recognized oral region homologies, based on the Universal Elemental Homology model for skeletal plates, in a wide range of fossil taxa. The oral region of echinoderms is mainly composed of the axial, or ambulacral, skeleton, which apparently evolved more slowly than the extraxial skeleton that forms the majority of the body. Recent phylogenetic hypotheses have focused on characters of the extraxial skeleton, which may have evolved too rapidly to preserve obvious homologies across all these groups. The axial skeleton conserved homologous suites of characters shared between various edrioasteroids and specific blastozoans, and between other blastozoans and crinoids. Although individual plates can be inferred as homologous, no directly overlapping suites of characters are shared between edrioasteroids and crinoids. Six different systems of mouth (peristome) plate organization (Peristomial Border Systems) are defined. These include four different systems based on the arrangement of the interradially-positioned oral plates and their peristomial cover plates, where PBS A1 occurs only in plesiomorphic edrioasteroids, PBS A2 occurs in plesiomorphic edrioasteroids and blastozoans, and PBS A3 and PBS A4 occur in blastozoans and crinoids. The other two systems have radially-positioned uniserial oral frame plates in construction of the mouth frame. PBS B1 has both orals and uniserial oral frame plates and occurs in edrioasterid and possibly edrioblastoid edrioasteroids, whereas PBS B2 has exclusively uniserial oral frame plates and is found in isorophid edrioasteroids and imbricate and gogiid blastozoans. These different types of mouth frame construction offer potential synapomorphies to aid in parsimony-based phylogenetics for exploring branching order among stem groups on the echinoderm tree of life.

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Localities bearing abundant enrolled Cambrian trilobites are extremely rare, but here we report a new and exceptional such assemblage with a high diversity of enrolled specimens from the middle Cambrian of Spain. This novel fi nd demonstrates that encapsulated enrollment was a behavioral response available to many of the early benthic trilobite morphotypes. This result provides a new perspective for reviewing the evolution of trilobite enrollment through the Paleozoic. We fi nd a signifi cant and consistent increase in the proportion of enrolled trilobites within assemblages bearing abundant articulated trilobites. Similarly, the mean number of coaptative devices also increased progressively during the Paleozoic. Such devices likely provided later enrolled trilobites with greater structural integrity, and may support an escalatory model of trilobite defense evolution. Likewise, environmental circumstances favoring the preservation of enrolled trilobites may have become more common during post-Cambrian time.on June 4, 2015 geology.gsapubs.org Downloaded from