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Journal of Paleontology 91(6):1220–1227
by “an anterior bar that is directed sharply upward” (von Bitter, 1972, p. 71), whereas the A2 element possesses a ‘posterior’ process with “upswept posterior end” (Baesemann, 1973, p. 706).Matsuda (1981), however, gives the clearest explanation for the morphology of the Sb element. According to him, the ‘anterior’ process of the element bends ‘inward’ around a cusp and the ‘inner’ surface of the ‘anterior’ process faces slightly ‘upward’ as a result of twisting at the bend. It seems that all previously illustrated S1–2 elements of Hindeodus possess a process with a similar bend and twist. The present study describes the bent and twisted process of a digyrate element as an ‘outer lateral’ process. That is, the S1–2 element bears two ‘lateral’ processes and bends around the cusp; the ‘outer lateral’ process twists at the bend and turns its ‘posterior’ surface ‘upward.’ The ‘outer lateral’ process, which can be compared with the ‘anterior’ processes or bars of Sweet (1970b), von Bitter (1972), Matsuda (1981), and Kozur (1996), and the ‘posterior’ process of Baesemann (1973), extends caudally in the conodont apparatus.
Conclusions
Although previous multielement reconstructions have strongly suggested a similarity between the apparatuses of Hindeodus and other ozarkodinids, the natural assemblages described by Agematsu et al. (2015) were insufficient to determine whether the S1 element was present. In this study, SR–μCT images of H. parvus specimens show that the element composition is consistent with the multielement definition of this genus given by Sweet (1977) and that the 15-element plan is quite similar to a well-known ozarkodinid model. These data will be useful for future studies of the classification and phylogeny of Hindeodus.
Accessibility of supplemental data
Data available from the Dryad Digital Repository:
http://dx.doi. org/10.5061/dryad.488rt Acknowledgments
We express sincere thanks to M.J. Orchard for his useful sug- gestions and comments. The synchrotron radiation experiments were performed at the BL20B2 of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2014B1442).
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