Coelacanth Lung: Breathing & Hearing in Ancient Fish

The coelacanth, often dubbed a “living fossil,” continues to yield evolutionary secrets. Recent research, leveraging advanced imaging techniques, isn’t just confirming what we thought we knew about these ancient fish – it’s fundamentally reshaping our understanding of the vertebrate transition from water to land. This isn’t simply paleontological curiosity; it’s a re-evaluation of the very mechanisms driving major evolutionary leaps, with implications for developmental biology and even our understanding of genetic potential.

For decades, the coelacanth has been a source of fascination, largely due to its perceived stasis – its apparent lack of significant change over millions of years. However, this narrative is increasingly being challenged. The research, drawing on studies spanning from the histological structure of fossilized lungs (Brito et al., 2010) to the detailed anatomical reconstruction of Mesozoic specimens (Manuelli et al., 2024), demonstrates a more dynamic evolutionary history. The application of propagation phase-contrast synchrotron X-ray micro-computed tomography (as detailed by Mirone et al., 2014; Paganin et al., 2002; and utilized in the recent Graulia studies – Manuelli et al., 2025) is the key enabler here. This allows scientists to visualize internal structures with a resolution previously unattainable, revealing subtle but critical anatomical features.

The focus on the inner ear (Fritzsch, 1987; Fritzsch et al., 2023; Bernstein, 2003) is particularly compelling. The coelacanth’s inner ear exhibits features previously thought to be exclusive to tetrapods, suggesting a closer evolutionary relationship than previously understood. This challenges the traditional view of lungfish as the primary link between fish and tetrapods, opening up new avenues for investigating the origins of hearing and balance in terrestrial vertebrates. Furthermore, the research into lung structure (Cupello, 2015; 2017; 2022; Cupello et al., 2024) and its associated vasculature is shedding light on how these organs evolved to facilitate air-breathing, a crucial step in the water-to-land transition (Perry et al., 2001). The discovery of the Graulia branchiodonta fossil (Manuelli et al., 2025; Ferrante & Cavin, 2025) and its detailed reconstruction provides a critical link in understanding the evolution of these features in extinct coelacanth species.

The Forward Look: The implications of these findings extend beyond paleontology. The identification of genetic mechanisms underlying these anatomical features – work hinted at by Bi et al., 2021 – will be the next major frontier. We can anticipate a surge in genomic research focused on coelacanths, aiming to pinpoint the genes responsible for the development of the inner ear and lungs. Moreover, the advanced imaging techniques employed in these studies will likely be applied to other “living fossil” species, potentially unlocking further secrets about evolutionary history. The ongoing debate about whether the lung or the ability to breathe air came first (Perry et al., 2001; Cavin & Guinot, 2014) will likely be refined with further investigation into the coelacanth’s respiratory system. Finally, expect increased scrutiny of coelacanth populations (Nulens et al., 2011) as conservation efforts become more critical in preserving these invaluable windows into our planet’s past. The detailed neurocranial development studies (Dutel et al., 2019; Dutel & Tafforeau, 2024) will undoubtedly fuel further research into the evolution of the vertebrate head and brain.