Challenging Darwin: Evolution of Triassic Conodonts and Their Struggle for Life in a Changing World

Abstract

Abstract The phylogeny and distribution of Triassic conodonts reveal many aspects of their natural history. Conodonts incorporate the morphologic response to temperature as well as to eustatic cycles. Speciation, radiation, and extinction are not fortuitous and evolution uses heterochrony (progenesis and neoteny) in response to stress-generating events. Proteromorphosis (reappearance of ancestral morphs) and paedomorphosis (retention of juvenile traits) is a reaction to sublethal environmental stress. This often follows radiation of fully developed forms in the recovery stage after extinction that timely matches transgressions. Evolutionary retrogradation (neoteny) during eustatic high stands often precedes extinction. The 51-Ma long Triassic Period consists of the Induan–Olenekian first 5 Ma with a post Permian extinction recovery rate of 13 speciations/Ma. The next 10 Ma of the Anisian–Ladinian saw a drop in speciations to 8 S/Ma, but during the remaining Carnian–Rhaetian 36 Ma, the rate was down to below 2 S/Ma, until the end of the Triassic. Roughly a dozen Permian survivors became extinct during the Induan. Soon after, Gondolellidae saw a revival with the Neospathodus–Kashmirella lineage. The Paragondolella–Misikella lineage emerged in the Aegean (Early Anisian) and dominated the Triassic scene for the next 45 Ma until extinction. In pelagic environments Gladigondolellidae ranged from Late Spathian until Mid-Carnian. Neogondolella became extinct by the Late Ladinian, and Paragondolella was replaced by Metapolygnathus during Julian times. The evolutionary trends of a free blade, platform adornment, widening of the posterior end, and bifurcation of the basal cavity were initiated sporadically during Late Ladinian and became the norm, reaching their peak in Early Norian Ancyrogondolella. Strongly ornamented Mazzaella and Carnepigondolella marked the Julian Pluvial Event and the Late Tuvalian LST (lowstand systems tract). The atavistic (neotenic) Norigondolella came in around the Tuvalian–Lacian boundary and a generalized posterior acumination set in with Alaunian (Middle Norian) Mockina. Catastrophes of various origin, such as global LST events and temperature rises, precipitated retrogradation with Dienerian Neospathodus, Pelsonian Nicoraella, Illyrian Pseudofurnishius, Cordevolian Mosherella, Tuvalian Neocavitella, and Sevatian–Rhaetian Misikella. Bithynian Kamuellerella–Ketinella–Gedikella in the Istanbul Zone define a North Tethyan Prepontic faunal subprovince. Late Anisian early forms of Pseudofurnishius initiated a Ladinian Sephardic faunal Province along the northern Gondwanian shelf. A stepwise decrease in speciation linked Triassic conodont evolution in unison to climatic–eustatic events.