Corallite increase and mural pores in <i>Lichenaria</i> (Tabulata, Ordovician)

다국어 초록 (Multilingual Abstract)

<P><I>Lichenaria</I> may be a representative of the most primitive stock of tabulate corals. The degree of paleobiologic complexity discovered in <I>L. globularis</I> and <I>L. grandis</I> is therefore surprising. Six types of corallite increase are recognized. All are lateral, which is the predominant mode in tabulates. Most types, however, are unique or are comparable to those in few other Ordovician taxa. Only Type 1 (<I>L. globularis</I>), yielding a single offset with a simple basal mural pore, is typical of tabulates. In Type 2 (<I>L. globularis</I>), one parent produces two offsets simultaneously, whereas in Type 3 (<I>L. globularis</I>), two offsets arise from separate parents at nearly the same time and join via a connective mural pore. Types 4 (<I>L. globularis, L. grandis</I>), 5 (<I>L. grandis</I>), and 6 (<I>L. globularis, L. grandis</I>), respectively, involve one, two, and two to four corallites in addition to the parent, which join via a connective mural pore at the site of offsetting.</P><P>Several features of <I>L. globularis</I> and <I>L. grandis</I> point to unexpectedly high levels of colony integration. Continuously fused common walls lacking back-to-back epithecae suggest soft tissue continuity among polyps above the corallum. Connective mural pores indicate temporary fusion of polyps. Coordinated behavior of polyps is suggested by the development of conjoined offsets from two parents during Type 3 increase, and by fusion during Types 4 to 6 increase. Attempts at certain types of increase sometimes failed to yield offsets, suggesting expendability of incipient buds, perhaps reflecting subjugation of individuals for the good of the colony.</P><P>In light of this study, genera that have previously been included in Lichenariidae and Lichenariida require reassessment and their phylogenetic relationships should be reconsidered. Unfortunately, this is hindered because fundamental characters such as corallite increase and wall structure remain inadequately known in most early tabulates.</P>