Stratigraphic column of the Xiazhen Formation with the 18 stromatoporoid-bearing intervals (clathrodictyid stromatoporoids)

<p><span>Clathrodictyids are the most abundant stromatoporoids in the Upper Ordovician Xiazhen Formation (middle to upper Katian) of South China. </span><span>A total of nine species belonging to four clathrodictyid genera are identified in the formation, including <em>Clathrodictyon idense (</em>Webby and Banks, 1976), <em>Clathrodictyon</em> cf. <em>Cl. microundulatum</em> (Nestor, 1964), <em>Clathrodictyon</em> cf. <em>Cl. mammillatum</em>  (Schmidt, 1858), <em>Clathrodictyon megalamellatum</em> Jeon n. sp., <em>Clathrodictyon plicatum</em> (Webby and Banks, 1976), <em>Ecclimadictyon nestori</em> Webby, 1969, <em>Ecclimadictyon undatum</em> (Webby and Banks, 1976), <em>Camptodictyon amzassensis</em> (Khalfina, 1960) and <em>Labyrinthodictyon cascum </em>(Webby and Morris, 1976). The </span><span>clathrodictyid fauna</span><span> in the Xiazhen Formation is very similar to those from both New South Wales and Tasmania, although the latter two Australian regions do not share any common clathrodictyid species during the Late Ordovician. The paleobiogeographic pattern indicates that the northward drift of South China resulted in a favorable environment for the migration of clathrodictyids from other peri-Gondwanan terranes to South China. Also, these peri-Gondwanan clathrodictyid species hosted various endobionts, representing a variety of paleoecological interactions. The high abundance and species-level diversity of clathrodictyid species presumably increased the substrate availability of </span><span>suitable host taxa,</span><span> judging from the diverse intergrowth associations between clathrodictyids and other benthic organisms. These paleoecological interactions between stromatoporoid and other organisms are known from the Late Ordovician and became more abundant and widespread in the Siluro–Devonian. Overall, the Late Ordovician clathrodictyid assemblage in South China demonstrates one of the highest species-level diversities among all </span><span>peri-Gondwanan terranes</span><span> and represents a precursor of the complex, clathrodictyid-dominanted communities of later metazoan reefs</span> <span>during the Great Ordovician Biodiversification Event.</span></p>