Conodonts versus triassic climatic and eustatic changes

Abstract

From astronomical, sedimentological, paleo-geographical and geochemical points of view, there is a general agreement that the Triassic period was exceptionally warm. The 51 MA long Triassic period started during the Siberian Traps and ended at the height of the Central Atlantic Magmatic Province activity. It is comprised between End Permian and End Triassic mass extinctions. Conodonts survived the former but got extinct by the end of the latter. Three major waves characterise the evolution of Triassic conodonts:

I. The 5 MA long Scythian recovery by intensive speciation (23 S/MA);

II. The 10 MA long Dinarian of intensive radiation (8.5 S/MA);

III. The 16 MA long Julian - Lacian survival (2S/MA) and 20 MA of Alaunian Rhaetian decline until extinction.

The major causes of stress affecting the evolution of Triassic conodonts are environmental, such as marine regressions, anoxic episodes, and thermal or trophic (nutritional) stress. These stressful episodes caused dwarfing and extinction of larger forms (r selection). Smaller forms with a short life span and rapid proliferation are the result of heterochrony such as proteromorphic retrogradation (Atavism).

The disappearance of the conodonts was not caused by a single mass extinction event, but the result of summing up stress factors from hostile environments over a long time.