Abstract

The response of conodont-phylogeny to eustatic cycles is examined. Speciation, radiation and extinction are not fortuitous and evolution uses diverse strategies to cope with events such as heterochrony (progenesis and neoteny).

Basinal gondolellid-, outer shelf ellisoniid- and inner shelf Hindeodus-apparatus bearing conodontophorids flitted by the Permo-Triassic boundary.

Hindeodus, best adapted to the eustatic lowstand that prevailed in Late Permian, vanished in early Induan. The radiation of ellisoniids in newly conquered Olenekian epicratonic shelf environments ended in late Spathian.

Triassic conodont evolution is well paced by the speciation and extinction of gondolellid morphs: iterating Dienerian to Rhaetian progenetic cavital neospathid morphs, radiation of the Smithian to Ladinian genus Neogondolella, advent of a short lived Spathian genus Plativillosus and radiation of the late Spathian to Norian genus Paragondolella.

The late Spathian through early Carnian range of the equatorial-Tethyan and basinal genus Gladigondolella seems to correspond to a relatively higher global sea level stand. Neogondolella was dominant on the shelf and so were the short lived Ladinian Pseudofurnishius and Sephardiella. Paragondolella occupied Middle Triassic basinal niches before spreading to Carnian shelf environments as a result of an early Carnian extinction and salinity crisis.

Radiation recurred in the late Carnian and early Norian with the appearance of offsprings of the genus Paragondolella, the genera Ancyrogondolella (emend.) and Epigondolella (emend.). The unfolding of new features in the phylogeny of conodonts came virtually to a halt by middle Norian and the ultimate means of survival was paedo-morphosis. The repetition of ancestral morphs in the Norian was followed by the return of neospathid morphs in the Rhaetian. The neospathid cryptic encoding of gondolellid features which permitted their survival from Induan into Olenekian times, merely signaling Anisian, Ladinian and Carnian crises, became critical in terminal Rhaetian times and ultimately vain.

The conodont taxonomic diversity curve reached peaks in the Smithian, Spathian and Ladinian only, and relates radiation to transgression. Epoch boundaries correspond to eustatic lows and decline in diversity. Extreme extinctions are related to sharp diminution of the world-ocean.