Ancient preen oil: Researchers discover 48-million-year-old lipids in a fossil bird

48-million-year old bird fossil excavated at the “Messel Pit“ in Germany. Markings show the uropygial gland.

As a rule, soft parts do not withstand the ravages of time; hence, the majority of vertebrate fossils consist only of bones. Under these circumstances, a new discovery from the UNESCO World Heritage Site "Messel Pit" near Darmstadt in Germany comes as an even bigger surprise: a 48-million-year old skin gland from a bird, containing lipids of the same age. The oldest lipids ever recorded in a fossil vertebrate were used by the bird to preen its plumage. The study is now published in the scientific journal Royal Society Proceedings B.

Birds spend a large amount of time preening their plumage. This makes sense, since the set of feathers adds to each bird's particular appearance, isolates and enables them to fly. In this preening ritual, the uropygial gland, located at the lower end of the bird's back, plays an important role. It produces an oily secretion used by the birds to grease their plumage in order to render it smoother and water-repellent.

Together with a group of international colleagues, Dr. Gerald Mayr, head of the Ornithology Section at the Senckenberg Research Institute, now discovered the oldest occurrence of such preen oils in birds known to date. With an age of 48 million years, this ancient preen oil constitutes a small scientific sensation. "The discovery is one of the most astonishing examples of soft part preservation in animals. It is extremely rare for something like this to be preserved for such a long time," says Mayr.

The organic materials that the soft parts consist of usually decompose within decades, or even just a few years. Several-million-year-old feathers and fur remnants are only known from a small number of fossil sites to date, including the oxygen-poor oil shale deposits of the Messel fossil site. This site also yielded the uropygial gland and the contained lipids examined in the course of this study.

"As shown by our detailed chemical analysis, the lipids have kept their original chemical composition, at least in part, over a span of 48 million years. The long-chain hydrocarbon compounds from the fossil remains of the uropygial gland can clearly be differentiated from the oil shale surrounding the fossil," explains Mayr. The analysis offers proof that the fossil artifact constitutes one of the oldest preserved uropygial glands -- a suspicion which had already been suggested by the arrangement at the fossil bird skeleton, albeit not finally confirmed.

To date, it is not clear why the lipids from the uropygial gland were able to survive for so long. It is possible that hey hardened into nore decomposition-resistant waxes under exclusion of oxygen. In addition, the researchers assume that one of the properties of the preen oil played a role that is still shown by modern birds today -- its antibacterial components. They may have been the reason that after the bird's death only few bacteria were able to settle in, preventing the full-on decomposition.

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