Late Triassic (Norian) Conodont Apparatuses Revealed by Conodont Clusters from Yunnan Province, Southwestern China

Almost all aspects of conodont research rely on a sound taxonomy based on comparative analysis. This is founded on hypotheses of homology which ultimately rest on knowledge of the location of elements in the apparatus. Natural assemblages-fossils that preserve the articulated remains of the conodont skeletal apparatus-provide our only direct evidence for element location, but very few are known from the Late Triassic. Here we describe fused clusters (natural assemblages) from the late Norian limestone beds of the Nanshuba Formation in Baoshan, Yunnan Province, southwestern China. Recurrent arrangements and juxtaposition of S and M elements in multiple clusters reveal the composition of the apparatus of Mockina and, probably, Parvigondolella. They indicate that these taxa had a standard 15 elements ozarkodinid apparatus, and provide new insights into the morphology of the elements occupying the P-2, M and S locations of the apparatus. The apparatus comprised a single alate (hibbardelliform) S-0 element, paired breviform digyrate (grodelliform) S-1 and (enantiognathiform) S-2 elements, paired bipennate (hindeodelliform) S-3 and S-4 elements, paired breviform digyrate (cypridodellifrom) M elements, paired, modified-angulate P-2 elements (with reduced or lacking 'posterior' process) and segminiplanate (mockiniform and parvigondolelliform) P-1 elements. Our results will allow testing of the hypothesis that Mockina, Parvigondolella and Misikella-critical taxa in Late Triassic biostratigraphy-are closely related and possessed morphologically similar elements in homologous locations.

Automated summary

The study relies on natural assemblages from late Norian limestone beds in southwestern China to describe the apparatus composition and element morphology of Mockina and Parvigondolella. The findings provide insights into the relationships and morphological similarities of critical Late Triassic taxa.