Deciphering the biomarkers of amber as a tool for the reconstruction of Mesozoic forest environments
Résumé
The Cheirolepidiaceae is an extinct family of conifers which was very common in the Mesozoic
era (-252 to -66 Ma), and was likely a major contributor to lignite and coal formation. The
differentiation of cheirolepids from other conifer families is pivotal to reconstructing the
terrestrial paleoenvironments. This should be possible through the chemical characterization of
amber, the polymerized fossil form of tree resins that consist of a complex mixture of terpenoids
and is often found associated with lignite and coal. As an extinct family, however, the
Cheirolepidiaceae has no modern relatives which could permit the direct assessment of specific
biomarkers, as is the case with extant families. Here we propose a cheirolepidiaceous
'fingerprint', based on the TC-GC/MS analysis of 25 samples of various Cretaceous amber from
France and Lebanon, and their comparison to a Triassic Italian and a Cretaceous Spanish ambers
that almost certainly originated from a cheirolepid based on the associated plant fossils. Thus the
presence, simultaneously, of callitrisate, phenolic diterpenes, labdanoic acids, and their respective
derivatives, is considered indicative of a cheirolepidiaceous resin. The differentiation of the
botanical sources of amber might allow for a refined evaluation of the resin production through
geological times and, along with the biological inclusions fossilized in amber, a more accurate
reconstruction of Mesozoic forest environments.