THE MODULAR ORGANIZATION OF THE TRILOBITE HEAD
Newly collected three-dimensionally preserved material of the trilobite Ceraurus pleurexanthemus was examined to assess whether these results are consistent in three-dimensions (3D). Morphologically mature silicified cranidia were picked from sieved residues of dissolved rock and then microCT scanned. To rigorously quantify shape, 3D meshes were produced from scan reconstructions and high-density geometric morphometrics was performed. In the most complex modular hypothesis, landmarks were divided into eight (8) partitions and the degree and structure of modularity was assessed using CR and the associated effect size measure as before. Results of 3D analyses are consistent with prior 2D analyses. The eyes highly covary with the anterior glabella with and without inclusion of the eye ridges. The developmental coupling of the eyes with the anteriormost region of the head may have imposed a constraint on patterns of diversification that may have either impeded or enhanced the rate of evolution depending on its congruence with selective pressures. Assessment of this will require further study of modularity across trilobite groups throughout the Paleozoic.