984


Journal of Paleontology


Figure 2. Stratigraphic correlation chart showing units with occurrences of Pilophyllia and Neopilophyllia n. gen. examined and cited in this paper, indicated in red font. Modified after Rong et al. (2012).


echoed by subsequent authors (e.g., He et al., 1989; Chen et al., 1997; He and Tang, 2013; McLean and Copper, 2013). Our study shows that the trabeculae, when well developed, are commonly comprised of coarse diverging rods of the secondary trabeculae, particularly as shown in transverse sections depicted herein (Figs. 4−16). Although we follow the widely accepted rhabdacanthine


interpretation, it should be noted that rhabdacanthine septa in the Pilophyllia-Neopilophyllia group are radially continuous, and therefore not acanthine, and rhabdacanths are seemingly completely comprised of fibrous tissues. Such observations do not completely conform to the classical definition of rhabdacanths by Hill (1936, 1981), in which each secondary trabecula is invested by lamellar tissues, as typically represented in some cystiphyllid corals such as Tryplasma Lonsdale, 1845.


Our study also shows that septa in all elements of the


pre-middle Telychian fauna are composed of club-shaped rhabdacanths or trabeculae of unknown original microstructure (e.g., Fig. 3.1), whereas the type of septal microstructure had apparently diversified in the succeeding middle Telychian fauna (e.g., Fig. 3.2−3.4). Of particular interest is the first appearance of wedge-shaped rhabdacanths in septa of species of Neopilo- phyllia n. gen. during the middle Telychian, probably marking a significant stage in the evolution of Silurian amplexoid corals. At the same time, the appearance of forms with septa entirely consisting of lamellar tissues, as in P. involuta, might have represented retrogressive forms, because this kind of septal microstructure is characteristic of forms such as Amplexoides Wang, 1947 and Synamplexoides Stern, 1956, among others, which are considered primitive by most authors (e.g., Wang


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