Gondolelloid multielement conodont apparatus (Scythogondolella) from the Lower Triassic of Jiangsu, East China, revealed by high-resolution X-ray microtomography

摘要

The application of high-resolution X-ray microtomography on conodont natural assemblages has provided new information on the structure of the elements and enabled the three-dimensional reconstruction of apparatuses. We herein report four conodont natural assemblages from uppermost Lower Qinglong Formation, Longtan, Nanjing, East China. Using X-ray microtomography, we reconstructed the apparatus of the end-Smithian (Olenekian, Early Trassic) Scythogondolella milleri. Our result confirms that Scythogondolella has an octomembrate apparatus composed of 15 elements (a single S0 element, two pairs of S1_4, M and P1_2 elements) like other gondolelloid apparatuses that have been tested by their corresponding natural assemblages, including Neogondolella, Novispathodus and Nicoraella. Element morphology of Scythogondolella closely resembles that of Neogondolella apparatus from the Illyrian (Anisian, Middle Triassic) of Monte San Giorgio: an alate (hibbardellan) S0 element with two long lateral processes that meet at a denticle anterior of the cusp, a bipennate (hindeodellan) S3 element with a bifurcated anterior process branching from the third denticle anterior of the cusp and an enantiognathiform S2 element with two dissimilar processes of nearly equal in length. It differs from the latter in the length of the inner-lateral process of M element and the posterior process of S0 and S3_4 elements without considering the obvious morphological differences in P elements between them. The element positional homologues of Scythogondolella conforms to those of the standard 15-element plan shared primitively among ozarkodinin, prioniodinin and prioniodontid conodonts, and again confirms that the breviform digyrate elements of cypridodellan and enantiognathiform morphotypes occupy the S1 and S2 positions, respectively, within the superfamily Gondolelloidea.