55-Million-Year-Old Penguin Fossils Preserve Chemical Clues to a Warmer Antarctica

Ancient penguin bones from Seymour Island, near the Antarctic Peninsula, preserve more than the remains of the birds themselves — their chemical composition can also record environmental changes spanning millions of years, according to paleontologists from China University of Geosciences (Beijing). Seymour Island holds one of the world's richest and most continuous records of Eocene penguin fossils, spanning an interval of Antarctic climate history from the relatively warm, humid early Eocene to the cooler middle and late Eocene.

Because the fossils are rare, the researchers used micro-X-ray fluorescence (micro-XRF) scanning, a non-destructive technique that maps different chemical elements across a surface, instead of methods that could damage the bones. They found clear differences between penguin bones from separate geological periods: fossils dating to about 55 million years ago, from the early Eocene, contained substantially stronger signals of titanium, silicon and potassium than younger fossils from cooler periods.

The researchers interpreted the elevated titanium, silicon and potassium levels in the older fossils as evidence consistent with stronger continental weathering and greater terrestrial runoff during the warm, humid early Eocene. The irregular shapes and curved surfaces of the fossil bones made it difficult to keep scanning conditions consistent, so the team positioned the bones as horizontally as possible and kept a constant distance between the scanning head and the bone surface. The technique also picked up patterns of iron, manganese and sulfur that reflected chemical changes in the marine sediments surrounding the bones as they were buried.

The results suggest that the chemistry of fossil bones could complement established sources of paleoclimate evidence, such as marine sediment drilling and microfossil analysis, giving researchers another way to reconstruct Antarctica's distant past using existing fossil collections. The study, by Boyang Xia, Huaichun Wu and Quanguo Li, was published July 31 in the journal Fossil Record.