Phylogenetic and palaeobiological implications of a new Carboniferous rugose coral with unusual trait combinations from the Akiyoshi Terrane of Japan

Abstract

Morphologically and reproductively constrained colonial Rugosa were recovered from Late Carboniferous (possibly Bashkirian) strata of the Akiyoshi Terrane, south-west Japan. Individual corallites are very small (diameter c.1.7 mm) and exhibit a uniserial fasciculate form with a deep calice. The essential characteristics of the Rugosa, including walls, major and minor septa, tabulae and columellae, are present. However, each morphological component shows an end-member feature (e.g. thick walls for corallites with very small diameter and simple columella), especially consistent with rugose corals considering phylogenetic and structural constraints. Increase is parricidal, occurring only by dichotomous branching in the cardinal–counter plane. The combination of these components results in a somewhat unbalanced morphology, and is the basis for the establishment of Yamatophyllum ultimum gen. et sp. nov. It is likely that the new genus was a terminal lineage, an ephemeral evolutionary experiment within the rugosan clade. Interestingly, morphologically similar but phylogenetically distinct corals commonly appeared in the initial stages of both rugosan and scleractinian diversifications, suggesting restrictions on the available morphospace of corals throughout the Phanerozoic.http://zoobank.org/urn:lsid:zoobank.org:pub:F847EC54-28F3-405B-AC7A-459F60458FF0