Preservation of uropygial gland lipids in a 48-million-year-old bird

• Published in: Proceedings of the Royal Society. B, Biological sciences Vol. 284; no. 1865; p. 20171050
• Main Authors: O'Reilly, Shane, Summons, Roger, Mayr, Gerald, Vinther, Jakob
• Format: Journal Article
• Language: English
• Published: England The Royal Society 25.10.2017; The Royal Society Publishing
• Edition: Royal Society (Great Britain)
• Subjects: Alcohols; Aldehydes; Aliphatic compounds; Alkanes; Alkenes; Alkylbenzenes; Animals; Birds; Birds - anatomy & histology; Chains; Eocene; Esters; Exocrine Glands - anatomy & histology; Exocrine Glands - chemistry; Fatty acids; Feathers; Fossil Bird; Fossils; Fossils - anatomy & histology; Gas chromatography; Gas Chromatography-Mass Spectrometry; Geopolymers; Kerogen; Ketones; Lipids; Lipids - analysis; Mass spectroscopy; Melanin; Messel; Molecular Fossils; Oil shale; Organic chemistry; Palaeobiology; Paleontology; Porphyrins; Preservation; Pyrolysis; Sediments; Shale; Soft Tissue Preservation; Tissues; Uropygial Gland; molecular fossils; Eocene; fossil bird; uropygial gland; Messel; soft tissue preservation
• ISSN: 0962-8452; 1471-2954
• DOI: 10.1098/rspb.2017.1050

Although various kinds of organic molecules are known to occur in fossils and rocks, most soft tissue preservation in animals is attributed to melanin or porphyrins. Lipids are particularly stable over time—as diagenetically altered ‘geolipids’ or as major molecular constituents of kerogen or fossil ‘geopolymers’—and may be expected to be preserved in certain vertebrate tissues. Here we analysed lipid residues from the uropygial gland of an early Eocene bird using pyrolysis gas chromatography mass spectroscopy. We found a pattern of aliphatic molecules in the fossil gland that was distinct from the host oil shale sediment matrix and from feathers of the same fossil. The fossil gland contained abundant n-alkenes, n-alkanes and alkylbenzenes with chain lengths greater than 20, as well as functionalized long-chain aldehydes, ketones, alkylnitriles and alkylthiophenes that were not detected in host sediment or fossil feathers. By comparison with modern bird uropygial gland wax esters, we show that these molecular fossils are likely derived from endogenous wax ester fatty alcohols and fatty acids that survived initial decay and underwent early diagenetic geopolymerization. These data demonstrate the high fidelity preservation of the uropygial gland waxes and showcase the resilience of lipids over geologic time and their potential role in the exceptional preservation of lipid-rich tissues of macrofossils.