It has been a mystery why bird tracks from the Early Cretaceous have never been found in the southern hemisphere. Now they are there

Very different species of birds have been flying above the Antarctic region for much longer than expected. Traces have been found that are 120 million years old. The birds probably migrated south each summer, leaving some of their footprints in the sediment of what is now Australia. Researchers can determine a surprising amount from this new information.

For the first time, traces of Early Cretaceous birds have been found in the Southern Hemisphere, in addition to a single bone and a few feathers. That’s strange, because many fossils have already been found in the Northern Hemisphere. It is a great mystery to paleontologists why traces of birds have not previously been found in the southern areas, which were once part of the Gondwana landmass. Paleontologist Anthony Martin and colleagues from the Emory University in Atlanta they have now succeeded: they have found a number of bird footprints dating from 129 to 120 million years old in the Wonthaggi Formation in Victoria, Australia.

Exceptional tracker
“We were looking for someone with the time and the right talent to look for these fossil bird tracks in the chalk cliffs along Victoria’s coastline,” Martin explains. “We were very lucky that Melissa Lowery, one of the co-authors of the study, wanted to work on finding the archaic footprints. She is an exceptional tracker and when she found the prints we photographed, measured, drew and studied them closely. This way we were able to properly identify the makers of the tracks. We also compared the tracks with other tracks of Cretaceous archaic birds from other parts of the world. To do this, we plowed through a whole mountain of previous studies.”

When Australia was still attached to Antarctica
“We found that at least 27 fossil tracks were left in a relatively small area in Victoria by a variety of bird species that lived in the riverine area of ​​the estuary at least 120 million years ago. These tracks are not only the oldest in Australia, but also the oldest in the entire Southern Hemisphere. At the time, this part of Australia was still attached to Antarctica and was close to the South Pole,” says Martin.

Earliest known Gondwanan bird tracks: Wonthaggi Formation (Early Cretaceous), Victoria, AustraliaEarliest known Gondwanan bird tracks: Wonthaggi Formation (Early Cretaceous), Victoria, Australia
Traces of bird feet. Image: Martin et al.

But what did these birds actually look like? “We can’t say for sure what these animals looked like because we only have footprints to work with, but their size and shape were probably quite similar to the wading birds and shorebirds that walk and fly on Earth today. The smaller birds probably looked like oystercatchers, the larger ones like egrets,” says Martin.

On the menu
The researcher also thinks he knows a thing or two about the animals’ diet. “The same sediment layer that preserved their footprints also stored remains of small invertebrates, such as worms and insects. These early birds may have feasted on worms, insects and whatever other goodies lived in the sand and mud. The prints were made under polar conditions, so they were most likely made in the summer. This implies that these birds were summer visitors in the Antarctic and flew from the north. At the end of the summer they flew back to avoid the Arctic winter.”

Originated in the north
Martin delves into why so many more bird prints and fossils have been found in the Northern Hemisphere. “One of the reasons is that birds probably first originated, evolved and then spread around the world in the area that is now Europe and East Asia. So they had a head start in the north to leave their mark. But I think that birds in the Early Cretaceous were much more common in the Southern Hemisphere than we previously thought. We think this discovery will inspire other scientists. Now palaeontologists know what to look for, so hopefully more bird tracks will soon be found in Australian soil.”

Interact with dinosaurs
The paleontologist is already working on his next project that follows on from this. “Our follow-up study revolves around describing and interpreting dinosaur tracks found near these bird prints. We hope to report on this early next year. Then we have a more complete picture of the larger animals that lived along with the birds in these polar ecosystems, at least 120 million years ago in the mysterious southern landscape.