Apparatus architecture of Belodina (Conodonta): Interpretations based on fused clusters of Belodina compressa (Branson and Mehl, 1933) from the Middle Ordovician (Turinian) Plattin Limestone of Missouri and Iowa

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Abstract
Twelve fused clusters of conodont elements representing the apparatus of Belodina compressa (Branson and Mehl, 1933) were recovered from the Plattin Limestone (Turinian) near New London, Missouri, and Hanover, Iowa. These clusters show that the apparatus of B. compressa consisted of four morphologically distinct elements: eobelodiniform (M), compressiform (S1), grandiform (S2), and dispansiform (S3) elements. All four element types are also present in fused clusters of B. confluens Sweet, 1979, supporting the interpretation that Belodina had a quadrimembrate apparatus. The B. compressa clusters were recovered from pellet-rich wackestones that yielded relatively large and diverse conodont faunas, in which only the elements of B. compressa were fused. The elements of B. compressa present in the fused clusters may have been deposited in fecal pellets, where a higher concentration of calcium phosphate, combined with the relatively large surface area contacts between B. compressa elements, facilitated the fusing of these elements into clusters. These fused clusters provide the basis for interpretation of the apparatus architecture of Belodina.