Frogs have maintained their ecology over the past 45 million years, according to a new study led by University College Cork.
Falk etc.. showed that the geometry of melanosomes in the eyespots of fossil frogs of the Miocene and Eocene is similar to the geometry of melanosomes in the eyes of modern frogs. Image credit: Falk etc.., document number: 10.1016/j.isci.2025.114220.
For the study, the authors examined 45-million-year-old frog fossils from the Geiseltal paleontological site in central Germany.
Remarkably, the fossils preserved remnants of skin and layers of microscopic fossilized cellular structures called melanosomes.
These cellular structures synthesize, store and transport melanin, the pigment responsible for the color of skin, hair and eyes.
Like modern frogs, these melanosomes are found in different areas of the body, including the eyes, internal organs, and skin.
The shape of melanosomes varies in fossil and modern soft tissues, with the exception of the eyes and internal organs.
“We suspect that the shape of the melanosome is associated with a function that varies between tissues. This may include photoprotection and homeostasis,” said Dr Valentina Rossi, a researcher at University College Cork.
“It's interesting that because the shape of eye melanosomes has not changed for millions of years, we can assume that their function is still the same. There was no need for any evolutionary changes,” added Dr Daniel Falk, also from University College Cork.
“Some species retain ancestral traits rather than evolve new ones.”
“We know that frogs have maintained their lifestyles for at least 45 million years, including, for example, the need to see at dawn and at night for hunting and mating.”
For the first time, the study combined large datasets of modern and fossil melanosomes from the same group of animals.
The authors studied melanosomes using a modern electron microscope and synchrotron X-ray fluorescence analysis.
These techniques were not available when the fossils were first discovered in the early 20th century.
“Palaeontological studies that combine data from fossils and modern species can shed new light on evolution,” University College Cork professor Maria McNamara said.
“We are just beginning to recognize the potential of melanin to serve as an evolutionary signal.”
study was published this month in the magazine iScience.
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Daniel Falk etc.. Evolutionary constraints of anuran melanin over 45 million years. iSciencepublished online December 17, 2025; doi: 10.1016/j.isci.2025.114220
