A surprising discovery of 27 fossilized bird footprints dating back 120 to 128 million years ago is changing the way we look at bird evolution and migration. Found in the Wonthaggi Formation south of Melbourne, they were formed in the Early Cretaceous and were created by birds stepping across soft sand or mud.
The footprints are so old that they set foot across a planet where Australia is still connected to Antarctica, and they turn out to be the earliest tracks of Gondwanan birds. When we imagine dinosaurs, birds are not inserted into the picture, but this discovery proves that they were part of the ecosystem, and had already migrated to take advantage of the changing food availability at the poles.
Finding fossil prints like this is a remarkable achievement because they are difficult to spot, but because they are so rare, they are far behind the case of smooth birds. The Wondaki Formation, where they were found, has yielded only one bird bone fossil to date – a wishbone – as well as a few feathers, and the researchers say this is beyond surprising.
„Birds have very thin and small bones,” said first author Anthony Martin A Report, a professor in Emory University’s Department of Environmental Sciences. „Think of the potential for a sparrow to be protected in the Geological Register as opposed to an elephant.”
Looking for these subtle tell-tale signs falls under ichnology, which is the search for traces of life (looking for tracks, burrows, nests, and teeth marks), an area of focus for Martin. However, it was the keen eye of co-author Melissa Lowery, a local volunteer fossil hunter, that led to the discovery of the first prints in Wonthaggi in 2020.
„Melissa is incredibly good at finding fossil tracks,” Martin said. „Some of these tracks are tricky for me too, and I have a lot of experience and practice.”
Ancient prints have been particularly difficult to find since most of them are only exposed at low tide, but their coastal home means marine life, including algae, barnacles and molluscs, have been accessible to some. Peter Zwingels assisted in the preservation of delicate tracks. A taxidermist at the Museums Victoria Research Institute specializes in the use of molds and casts to preserve specimens such as swingels.
A good thing, too, is that many notable discoveries don’t hang around for long.
„The seven tracks Melissa found in 2020 no longer exist,” Martin continued. „Some fossils, including footprints, only emerge for a short time after being buried for millions of years. We humans need to hurry and document them before they disappear again.
The thesis has been published PLOS ONE.
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