ONTOGENY AND LIFE CYCLE OF PERMIAN GONDOLELLIDS

Over the past several decades histological studies have greatly advanced our understanding on conodont growth and function. Despite these advances, few have attempted to fully characterize the ontogenetic sequence of conodont elements, leaving significant gaps in our understanding of the conodont life cycle. Conodonts are known to have grown by the external apposition of lamellae, but it is not understood if this growth occurs in distinct phases. Utilizing a Field Emission Scanning Electron Microscope (FESEM), we analyzed a number of histological sections through platform elements of both Jinogondolella from the Middle Permian Bell Canyon Formation of West Texas, and Clarkina from the Upper Permian Ali Bashi Formation of Iran. Our observations reveal both physical and chemical characteristics that can be used to define the ontogeny of these platforms into three distinct phases. These phases include the juvenile phase, defined by large interlamellar spaces and high sulfur content; a sub-adult phase, defined by 0.3 micrometer growth laminations and minor repair structures; and an adult to gerontic phase, whereby a series of laminations of consistent thickness are added along the top of the element only in conjunction with increased reparative structures and at times an elevated fluorine content. These observations imply that conodont platform element growth is not homogeneous, and that functionality of conodont elements varies throughout the life cycle of the animal. Most significantly, the juvenile phase does not show any evidence of function or repair, indicating juvenile phase platform elements of Permian gondolellids do not emerge from the soft tissue until reaching the sub-adult phase of growth.