Natural assemblages of the earliest Triassic conodont Hindeodus parvus from the Shangsi section, Sichuan province, Southwest China

The morphology and number of elements in the Early Triassic conodont apparatus of the genus Hindeodus, particularly Hindeodus parvus (Kozur and Pjatakova, 1976), still remain controversial. In order to shed light on the apparatus composition of this iconic genus, here we report two well-preserved conodont natural assemblages of Hindeodus from the base of Member I of the Feixianguan Formation (Induan, lower Griesbachian, in age) at Shangsi section, Sichuan Province, Southwest China. These two natural assemblages preserve direct evidence of the number, morphology, and arrangement of elements in the apparatus of Hindeodus, and in particular H. parvus. The apparatus of H. parvus consists of six morphotype elements with S, M, and P positions, showing the typical ozarkodinid 15-element arrangement. The S1-S4 array comprises a set of nine ramiform elements: a crown-shaped alate element without a ‘posterior’ process situated at the S0 position, two inner pairs of digyrate elements positioned at the S1–2 positions, and two outer pairs of bipennate elements located at the S3 and S4 locations. A pair of dolabrate elements occupy the M position outside the S array. The paired P1 and P2 positions are occupied by carminiscaphate and angulate elements, respectively. The 15-element apparatus architecture for the genus, resembles the well-known template of ozarkodinid model, further indicating the conservative architecture of the apparatus in Order Ozarkodinida spanning more than 250 million years.