Ancient fish fossils reveal surprising details about cell preservation and age

Jim Crocker
4th December, 2025

Ancient fish fossils reveal surprising details about cell preservation and age

The recovery of microstructures resembling bone cells (osteocytes; e.g., A, N), blood vessels (e.g., G, K), and fibrous matrix (e.g., D, T) from the ~375-million-year-old fossils of diverse Devonian fish, including Bothriolepis and Megalichthys, extends the known record of exceptional soft-tissue preservation in vertebrates by approximately 100 million years.

Image adapted from: Rogoff, Ullmann / CC BY SA (Source)

Key Findings

  • This study discovered cell-like structures and blood vessels in 375 million-year-old fish fossils, extending the known timeframe for soft tissue preservation
  • The research shows that soft tissue preservation isn’t limited to recent fossils or specific environments, suggesting it may have begun with the evolution of bony skeletons
  • Chemical analysis indicates these structures contain original organic components, not just mineral replacements, offering potential for molecular study of ancient life
The study of fossilized remains has traditionally focused on hard structures like bone and teeth. However, recent research has revealed that soft tissues – such as blood vessels and cells – can sometimes be preserved within fossils, offering a unique window into the biology of extinct organisms. A key question has been whether this preservation is limited to relatively recent fossils, or if it extends much further back in geological time. Researchers from the University of Gothenburg, University of North Dakota and Rowan University have now pushed back the known limits of soft tissue preservation significantly, discovering evidence of cellular structures in fossils dating back to the Devonian period, approximately 375 million years ago[1]. The research team focused on fossils of Bothriolepis and other fish from the Late Devonian period. These early vertebrates represent a crucial stage in the evolution of jawed fishes and the development of bony skeletons. The core of the study involved a process called demineralization. Bones are largely composed of minerals, primarily calcium phosphate, that accumulate over time. To reveal any preserved soft tissues, these minerals must be carefully removed using chemical solutions. This process, when successful, leaves behind any remaining organic material and microscopic structures. Following demineralization, the researchers examined the resulting material using microscopy. They identified numerous microstructures resembling vertebrate osteocytes (bone cells), fragments of blood vessels, and sheets of fibrous bone matrix. Importantly, these structures weren’t just visually similar; they also exhibited chemical signatures suggesting the presence of some original organic components. This is crucial because it distinguishes between genuine preserved tissues and mineral replacements that merely look like tissues. This discovery is significant because it extends the known timeframe for soft tissue preservation by nearly 100 million years, predating previous findings substantially. Prior work had demonstrated the preservation of soft tissues in fossils from the Cretaceous and Jurassic periods[2][3], and even in a Tyrannosaurus rex specimen[4]. However, these discoveries were all relatively recent in geological terms. The new findings demonstrate that the conditions allowing for such preservation were present much earlier in vertebrate evolution. The implications of this research are far-reaching. It suggests that the preservation pathways for soft tissues aren’t necessarily tied to specific environmental conditions or geological ages. Instead, the ability to preserve these structures may have emerged alongside the evolution of vascularized, cellular bone in the early Paleozoic era. This challenges the assumption that older fossils are inherently less likely to contain preserved soft tissues. Previous studies have highlighted the importance of specific depositional environments in soft tissue preservation. For example, research on fossils from the Hornerstown Formation showed that marine vertebrate fossils preserved in glauconitic greensand could yield well-preserved cells and tissues, with darker-colored specimens exhibiting better preservation[3]. This suggests that certain geochemical conditions, such as those created by the presence of glauconite, can promote preservation. However, the new study indicates that preservation isn’t solely dependent on these specific environments, as the Devonian fish fossils were recovered from different geological settings. Furthermore, the research builds on the idea that the initial preservation process involves cross-linking of molecular components followed by mineralization[4]. This two-step mechanism could explain how soft tissues can remain intact for millions of years, protected within the mineralized bone matrix. The findings also support the notion that fossils displaying low trace element uptake are more likely to retain paleomolecular information[2], as the Devonian fish fossils exhibited evidence of limited chemical alteration after initial fossilization. The study demonstrates that the age of a fossil is a poor predictor of whether it will retain potentially-endogenous microstructures. This opens up exciting possibilities for future research, suggesting that a wider range of ancient fossils may hold valuable clues about the biology of extinct organisms than previously thought.

Animal ScienceEvolution

References

Main Study

1) Age is just a number: Examining the preservation of cells and soft tissues in Bothriolepis and other Devonian fish

Published 3rd December, 2025

https://doi.org/10.1371/journal.pone.0335783

Related Studies

2) Soft-Tissue, Rare Earth Element, and Molecular Analyses of Dreadnoughtus schrani, an Exceptionally Complete Titanosaur from Argentina.

https://doi.org/10.3390/biology11081158

3) Soft Tissue and Biomolecular Preservation in Vertebrate Fossils from Glauconitic, Shallow Marine Sediments of the Hornerstown Formation, Edelman Fossil Park, New Jersey.

https://doi.org/10.3390/biology11081161

4) Soft tissue and cellular preservation in vertebrate skeletal elements from the Cretaceous to the present.

Journal: Proceedings. Biological sciences, Issue: Vol 274, Issue 1607, Jan 2007


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