Paleontologists have discovered 27 bird footprints and other tracks, dating back to between 120 and 128 million years ago (Early Cretaceous era), in the Wonthaggi Formation of Victoria, Australia. The discovery opens another window into the evolution of early birds and their possible migratory behavior and confirms the earliest known presence of birds in Australia and the rest of the supercontinent Gondwana.
Cretaceous bird fossils are abundant and diverse on the northern continents, but extremely rare in the southern regions that were once part of the supercontinent Gondwana.
This presents a challenge for paleontologists trying to understand the distribution of early birds.
“The majority of bird tracks and body fossils dating to the Early Cretaceous come from the Northern Hemisphere, particularly Asia,” said Emory University professor Anthony Martin, first author of the study.
“Our discovery shows that there were many birds, and a variety of them, near the south pole about 125 million years ago.”
In their study, Professor Martin and his colleagues examined a series of bird tracks from the Lower Cretaceous Wonthaggi Formation, south of Melbourne, Victoria, Australia.
The 27 tracks vary in shape and size and indicate the presence of several different types of birds.
They measure 7 to 14 cm wide, similar to the tracks of modern shorebirds such as little herons and oystercatchers, and are among the largest known from the Early Cretaceous.
The tracks are present in multiple stratigraphic layers of an ancient polar floodplain, suggesting that these birds could have visited this area seasonally, perhaps as part of a migratory route.
“The birds would probably have been stepping on soft sand or mud,” Professor Martin said.
“Then the footprints may have been buried by the gentle flow of the river which deposited more sand or mud on top of them.”
Apart from a bone and some feathers, these footprints represent the oldest known evidence of birds that lived in Australia or any part of Gondwana, and also the oldest known evidence of birds that lived in ancient polar environments.
“We are very excited to document that a variety of birds lived in polar Australia during the Early Cretaceous epoch,” the authors said.
“But we also hope that our discovery of trace fossils will inspire other researchers to search and find more Early Cretaceous bird tracks in other parts of the Southern Hemisphere.”
The discovery is reported in a paper In the diary Plus one.
AJ Martin et al. 2023. The earliest known Gondwanan bird tracks: Wonthaggi Formation (Lower Cretaceous), Victoria, Australia. Plus one 18 (11): e0293308; doi: 10.1371/journal.pone.0293308