Proteromorphosis in Early Triassic Conodonts

Abstract

Herein we emphasise how environment, palaeoecology and palaeobiogeography play key roles in the evolution of organisms. Nineteenth-century ammonoid biochronology led to the definition of the Mesozoic stages. Their beginning and end are bound by the biggest mass extinctions of Earth history. This study deals with the initial Triassic stages that needed a remarkably short biotic recovery time. The Lower Triassic stages, all named after nineteenth-century researchers of the Himalayas, are the Griesbachian, Dienerian, Smithian and Spathian. If the twentieth century saw an increasing use of alternative biotic groups, among which were those conodonts and radiolarians that permit the relative timing of open marine sequences, one can say that twenty-first century isotopic excursion events became increasingly dominant. For the Early Triassic alone, the succession of positive and negative excursions determines the following five events: (I) Late Permian-Early Triassic boundary (II) Late Griesbachian (III) Dienerian-Smithian boundary (IV) Smithian-Spathian boundary (V) Middle Spathian-Early Aegean interval These events comprise three negative events (I, III and IV) and two positive events (II and V). The nature of these events, in control of environmental instabilities and system tracts (sea-level changes), is the key for understanding biological morphogenesis and evolution. This contribution aims to analyse the phenomena during one of the five largest mass extinctions of Earth history and the fast recovery that followed in its aftermath. Our study of the conodont subfamily Neogondolellinae suggests that stress-generating phenomena and events appear to have paced successive lineages, alternating from Darwinian anagenesis to atavistic reversal and rediversification. © Springer Nature Switzerland AG 2020.