Ultrastructure of 30–40 million year old leaflets from Dominican amber (Hymenaea protera, Fabaceae: Angiospermae)

Hymenaea protera leaflet fossils entombed in amber, dated at 30 to 40 million years (mine strata and exomethylene dating) were observed by both light and transmission electron microscopy. Ultrastructure preservation in these leaflets shows the presence of chloroplasts with thylakoid membranes, cell walls, mitochondria with associated endoplasmic reticulum, nuclei, and xylem tissue. Tissues show varying degrees of degradation; however, natural resin, which has perfused the cells, seems to maintain the structural integrity of the membranes and walls. We conclude that preservation of amber entombed organisms results from dehydration and slow fixative properties leaving the ultrastructure in excellent condition. These findings parallel reports on the exceptional preservation of amino acids and of DNA in amber-entombed organisms.