Conodont diversity and evolution through the latest Permian and Early Triassic upheavals

Abstract

A study of latest Permian and Early Triassic multielement conodonts identifies eight steps in their evolutionary history during an interval when Earth's biosphere was highly stressed. These steps are: 1) gradual decline of families and genera through the Changhsingian (up to the late Griesbachian); 2) conodont biofacies change and extinction of Tethyan endemic species close to the Permian–Triassic Boundary (PTB); 3) faunal turnover with extinction and origination in the late Griesbachian; 4) initial radiation in gondolellids and diversification in apparatuses during the Dienerian; 5) explosive radiation in the early–middle Smithian; 6) major extinction in the late Smithian; 7) major radiation early in the Spathian; 8) gradual turnover and decline in the late Spathian through early Anisian. Conodontophorids were reduced from five families at the beginning of the Changhsingian to three by the PTB, and to two late in the Griesbachian. From the Changhsingian to the late Griesbachian, there was a single multielement apparatus represented in the Gondolellidae, whereas by the Olenekian there were at least twelve. Given absolute age constraints, the conodont recovery in the aftermath of the PTB was extraordinary. Conodont evolution during the Dienerian remains obscure but was very significant in terms of changes in multielement apparatuses. In spite of Induan extinctions, generic diversity generally increased from the PTB up to the late Smithian. In terms of species, genera, and multielement apparatuses, the acme of Triassic conodonts was in the middle Smithian, and the biggest extinction was in the late Smithian. After this extinction, generic and apparatus diversity quickly returned to high levels, marking a significant Spathian recovery. Gradual decline characterized the late Spathian and persisted into the early Anisian. A synthetic summary of the temporal distribution and proposed relationships amongst all known Lower Triassic conodonts provide an improved foundation for biostratigraphic and biochronologic studies. Extinction and radiation trends correlate well with sea-level changes and sequence boundaries: faunal turnovers correspond to lowstands in the late Griesbachian, late Smithian, and late Spathian, and radiations correspond to transgressions in the early Griesbachian, early Smithian, and early Spathian. The trends also correlate with perturbations in the carbon cycle, with Lower Triassic δ 13C minima corresponding to extinction and faunal turnover, and positive values generally occurring during radiations. However, Middle Triassic recovery of marine benthos follows a positive maxima and an overall decline in conodont diversity. New taxa Borinella chowadensis, B. megacuspa, Neogondolella griesbachensis, and N. mongeri are described.