Chitin detected in 1.0 Ga old acritarch-like fossils from Lakhanda Lagerstätte and its implication for skeleton biomineralization

The co-evolution of life and minerals has profoundly shaped Earth's biological and geological history, with skeletal biomineralization emerging in eukaryotes over 800 Ma. Chitin, a key organic scaffold in modern biomineralization, was previously identified in fossils as old as the Cambrian (~505 Ma). Here, we extend this record by demonstrating the presence of fossilized chitin in 1-Ga acritarch-like fossils from the Lakhanda Lagerstätte, Siberia. These large spherical fossils (100–200 µm) align with the characteristics of acritarchs, organic-walled microfossils interpreted as cysts of planktonic protists. Spectroscopic analyses using nano-infrared spectroscopy of acritarch-like fossils showed molecular features diagnostic of chitin, including amide I and II bands and polysaccharide-related bands. These findings push back the timeline for chitin utilization in protists by 500 Ma, demonstrating its role in early biomineralization processes. This discovery highlights the significance of chitin in early protist evolution and its role in shaping biomineralization pathways. It also underscores the potential of advanced spectroscopy techniques to reveal the chemical and biological signatures of ancient life with unprecedented precision.