SYNCHROTRON X-RAY MICROTOMOGRAPHY: AN INSIGHT INTO UPPER TRIASSIC CONODONT ULTRASTRUCTURE

In order to study the ultrastructure and the ontogenetic processes of Late Triassic conodont P1 elements, we performed synchrotron x-ray microtomographies on 13 conodonts from the Pizzo Mondello section (Sicily, Italy; GSSP candidate for the Norian), providing internal tomographic images of Late Triassic conodonts for the first time. The analyses were performed at the Swiss Light Source of the Paul Scherrer Institut (Zurich, Switzerland), with the scanned conodonts belonging to 5 genera and 12 species (all of them phylogenetically related) and ranging from the Upper Carnian to the Lower Norian. The scanned specimens have two CAI values (1.5 and 7) and have different degrees of preservation. The synchrotron x-ray microscopy is a non-invasive tool and it has the great advantage to examine an almost unlimited number of sections per conodont that can be oriented in all the directions, allowing investigations of the inside of an element from all perspectives. The different kind of tissues and the internal ultrastructure are distinguishable at different levels in most parts of the scanned conodonts. Growth lines are visible in all parts of the platforms, providing valuable data concerning the growth processes of the P1 elements. In particular, it is possible to observe in detail the ontogenetic processes of some diagnostic morphological characters of the platforms, allowing us to distinguish homologies from analogies and thus, to unravel evolutionary convergences that, otherwise, could not be distinguished with other analytical techniques. X-ray synchrotron analysis is thus a reliable tool to investigate the internal structure of conodonts and to refine preexisting phylogenetic models.