THE LILLIPUT EFFECT IN CRINOIDS AT THE END OF THE OCEANIC ANOXIC EVENT 2: A CASE STUDY FROM POLAND

The Cretaceous period consists of many Oceanic Anoxic Events, likely stimulated by global greenhouse effect. The so-called Oceanic Anoxic Event 2 (OAE2) had occurred worldwide from the Late Cenomanian up to the Early-Middle Turonian, causing a significant faunal turn-over in marine biota pushing some species to the brink of extinction. It has been argued that numerous organisms had also undergone morphological changes, including reduction in size during this time. This anoxic event also drove other changes, including habitats or strategy of life. We show that stalkless crinoids (comatulids) from the oxygen-depleted Turonian sediments of Poland had adapted to unfavorable environmental conditions by reducing their body size. Furthermore, we demonstrate that at the moment when environmental factors become favorable again, these crinoids regained their regular (pre-event) size. This phenomenon likely illustrates the so-called “dwarfing”.