A new study lead by UCC palaeontologists discovered that frogs have conserved their ecology in the last 45 million years.
Dr Daniel Falk, together with colleagues from UCC, Germany and the United States, studied 45-million-year-old frogs from the Geiseltal fossil site in central Germany. Remarkably, the fossils preserve skin remnants and layers of microscopic fossilised cell structures called melanosomes. These cell structures synthesise, store, and transport melanin - the pigment responsible for skin, hair, and eye colour.
Similar to modern frogs, these melanosomes occur in different body areas including the eyes, the internal organs and the skin. The shape of the melanosomes is different in fossil and modern soft tissues, except for those in the eyes and internal organs.
"We suspect that melanosome shape is related to function, which varies between tissues. This can include photoprotection and homeostasis," said coauthor Dr Valentina Rossi, specialist for fossil melanosomes.
Dr Falk said:
"Interestingly, because the shape of eye melanosomes did not change over millions of years, we can assume that their function is still the same. There was no need for any evolutionary change. Some species are keeping ancestral traits instead of evolving new ones. We know that frogs retained their lifestyle for at least 45 million years and that included, for instance, the need to see at dawn and nighttime for hunting and mating."
This is the first time a study has combined large datasets of modern and fossil melanosomes from one animal group. The team studied the melanosomes using cutting edge electron microscope and synchrotron-X-ray fluorescence analyses. These techniques were not available when the fossils were first discovered in the early twentieth century.
"Palaeontological studies that integrate data from fossil and modern species have the power to shed new light on evolution" said senior author Prof. Maria McNamara.
"We are just beginning to realise the potential of melanin to serve as an evolutionary signal."
The study is part of a research cooperation between UCC, Martin-Luther-University Halle-Wittenberg (Germany), Natural History Museum Bamberg (Germany) and Stanford Synchrotron Radiation Lightsource (USA) with funding from the Irish Research Council, the European Research Council, Research Ireland and the U.S. Department of Energy. The study is published today in the journal iScience.
