New findings spearheaded by University College Cork indicate that amphibian ecological roles have remained consistent for the past 45 million years.
Falk et al. demonstrate a parallel in the configuration of melanosomes within the ocular regions of Miocene and Eocene fossilized frogs and those found in contemporary frogs. Image courtesy of Falk et al., doi: 10.1016/j.isci.2025.114220.
Within this investigation, researchers delved into frog specimens dating back 45 million years, unearthed from the Geiseltal paleontological site situated in central Germany.
Remarkably, these ancient specimens exhibit preserved dermal vestiges and layers of microscopic, fossilized cellular structures known as melanosomes.
These cellular components are instrumental in the synthesis, storage, and conveyance of melanin, the pigment responsible for imparting color to skin, hair, and eyes.
In a manner analogous to extant frogs, these melanosomes are distributed across various anatomical locations, including the ocular organs, internal viscera, and the integument.
A notable observation is the divergence in melanosome morphology between ancient and contemporary soft tissues, with the exception of those located in the eyes and internal organs.
“We postulate that the varied functional roles across different tissues, such as photoprotection and maintaining physiological balance, influence melanosome geometry,” stated Dr. Valentina Rossi, a research associate at University College Cork.
“Intriguingly, given the enduring shape of ocular melanosomes across millennia, we infer that their fundamental function has remained unchanged, obviating the necessity for any evolutionary modifications,” elaborated Dr. Daniel Falk, also affiliated with University College Cork.
“Certain species tend to preserve ancestral characteristics rather than undergo novel evolutionary development.”
“It is understood that frogs have sustained their way of life for a minimum of 45 million years, which importantly encompassed, for example, the imperative visual acuity required for nocturnal and crepuscular hunting and reproductive activities.”
This research marks the inaugural instance where a comprehensive analysis has integrated extensive datasets from both fossilized and modern melanosomes within a single vertebrate group.
The research team employed advanced electron microscopy and synchrotron X-ray fluorescence techniques for their melanosome examination.
These sophisticated analytical methods were unavailable during the initial discovery of the fossils in the early twentieth century.
“Paleontological investigations that incorporate data from both extinct and extant species possess the capacity to illuminate evolutionary processes with unprecedented clarity,” remarked Professor Maria McNamara of University College Cork.
“The potential of melanin as an indicator of evolutionary history is only beginning to be fully appreciated.”
This groundbreaking investigation was disseminated this month within the esteemed journal iScience.
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Daniel Falk et al. Evolutionary constraints on anuran melanin for 45 million years. iScience, published online December 17, 2025; doi: 10.1016/j.isci.2025.114220
