Organic inclusions in Brazilian Cretaceous amber: The oldest ostracods preserved in fossil resins

Abstract

Fossil resins and ostracods are well-known in Brazilian Cretaceous sedimentary Basins, especially in the Araripe Basin. The present work reports several ostracods encapsulated in an amber sample recovered from limestones of the Crato Formation (Araripe Basin, Northeastern Brazil). The amber was analyzed under optical and eletronic microscopy revealing several ostracod specimens. Considering the general morphology, the recovered specimens were attributed to the freshwater to brackish genera Pattersoncypris Bate, 1972 and Damonella Anderson, 1966 in the superfamily Cypridoidea. Additionally, palynological analyses of the limestone rock around the amber demonstrate the predominance of pollen grains of the Classopolis genus, produced by conifers of Cheirolepidiaceae family, suggesting this family as possible botanical source of the fossil resin. The proposed interpretation for this preservation is as follow: (i) the lake level variations transported the ostracods to the margin; (ii) drops of resin exuded from the trunk fell to the margin on the dead ostracods; (iii) the exposed resin underwent polymerization preserving the ostracods; (iv) and finally, the amber was preserved in the laminated calcareous deposit. The record described here provides a detailed study of organisms fossilized in Brazilian amber as well as it reports the oldest record of ostracods enclosed in fossil resins (Aptian age).