Rejuvenescences in Permian rugose coral Ipciphyllum naoticum in Xizang and their ecological implications
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Abstract:
This study focuses on the rejuvenescences in massive rugose coral Ipciphyllum naoticum from the Late Permian Gyanyima section in Xizang, southwest China. Two types of rejuvenescences, axial and lateral, are observed. Based on serial thin sections, the process of rejuvenescence is described. The skeletal characteristics of axial and lateral rejuvenescences in I. naoticum are significantly different, due to the regrowth of related corallite from different stages of ontogeny. The axial rejuvenated corallite regrow from an earlier juvenile stage. The diameter of the rejuvenated individuals significantly decreases, however, the axial columns of the original and rejuvenated corallites are not only continuous, but also have little change in size. This phenomenon may be due to the polyp being squeezed by adjacent polyps, reducing its space and making it more difficult to get sufficient food. Nutrient deficiency leads to a decrease in corallite diameter. The lateral rejuvenated corallite regrow from the brephic stage, and subsequently build new axial column, independent of the axial column of the original corallite. This phenomenon may be related to polyp health or injury. The regrowth of rejuvenated corals from the brephic stage or a younger stage depends on the overall condition of the polyp. If the polyp is relatively healthy, it may regrow from a younger stage. If only remnant tissue fragments survive, the rejuvenated coral may secrete skeleton from the brephic stage. In this study, the size of remnant tissue fragments of the lateral rejuvenated corallite that regrow from the brephic stage is limited. It can be inferred that the polyp fragments of some rugose corals, including I. naoticum, can also regrow like extant corals. In massive corals, individual rejuvenation may be related to the overall condition of the polyps, including injury and intraspecific competition, rather than the surrounding environment.
