plosone-phylo
Figure 1
Opposing views on the interpretation of trilobite trunk segmentation and alternative phylogenetic hypotheses for the group.A. Direct correspondence between the segments and the dorsal exoskeletal plates (i.e. tergites) [11], [14]?[16], illustrated in the corynexochid Olenoides serratus; this interpretation is reflective of the plesiomorphic trunk segmentation present in most arthropods, in which the segment and tergite borders are coincident. Every second segment is shaded. A1. Morphological features and articulating devices of a typical trunk tergite, dorsal view. B. Indirect correspondence between segments and tergites [12], [19], [20]; the intersegmental boundaries of the trunk occur within each tergite, being delimited by the articulating (af) and pleural (pf) furrows. C. Trilobites have been variously interpreted as stem-euarthropods, stem-chelicerates, and stem-mandibulates [24], although most recent studies favour the latter affinities. The position of trilobites within total-group Euarthropoda indicates that the segment polarity gene engrailed had a role in the segmentation of these extinct organisms. Other abbreviations: ahr, articulating half ring; fp, fulcral process.
Figure 1
Opposing views on the interpretation of trilobite trunk segmentation and alternative phylogenetic hypotheses for the group.A. Direct correspondence between the segments and the dorsal exoskeletal plates (i.e. tergites) [11], [14]?[16], illustrated in the corynexochid Olenoides serratus; this interpretation is reflective of the plesiomorphic trunk segmentation present in most arthropods, in which the segment and tergite borders are coincident. Every second segment is shaded. A1. Morphological features and articulating devices of a typical trunk tergite, dorsal view. B. Indirect correspondence between segments and tergites [12], [19], [20]; the intersegmental boundaries of the trunk occur within each tergite, being delimited by the articulating (af) and pleural (pf) furrows. C. Trilobites have been variously interpreted as stem-euarthropods, stem-chelicerates, and stem-mandibulates [24], although most recent studies favour the latter affinities. The position of trilobites within total-group Euarthropoda indicates that the segment polarity gene engrailed had a role in the segmentation of these extinct organisms. Other abbreviations: ahr, articulating half ring; fp, fulcral process.