Onocerane attests to dry climatic events during the Quaternary in the tropics

An unusual molecular fossil (onocerane I) has been detected in Quaternary lacustrine sediments (Lagoa do Caçó, NE Brazil) for the first time. This component was initially thought to attest to the former presence of ferns or club mosses. From consideration of possible plant precursors of onocerane-related molecules recorded in the literature and comparison with palynological results and palaeoclimatic data, we here provide evidence that club mosses and ferns cannot account as sources of onocerane I in this setting. Onocerane I is abundant in the lipid extracts of sediments deposited during the two driest periods recorded in Northern Brazil (Last Glacial Maximum and Younger Dryas). This component is therefore suspected to be diagnostic of the development of plants adapted to dry or semi-arid conditions in this region.