Oldest known bird footprints discovered in Australia

In a significant breakthrough in the field of paleontology, the southern coast of Australia has revealed 27 ancient bird footprints.

These footprints date back to the Early Cretaceous period when Australia was still physically connected to Antarctica. They offer new insights into early avian evolution and their migratory patterns.

The bird tracks are estimated to be between 120 and 128 million years old, a time frame that is crucial to understanding the early stages of avian evolution.

125 million-year-old bird tracks

Anthony Martin is the first author of the study and a professor at Emory University‘s Department of Environmental Sciences. He emphasizes the global significance of this discovery.

“Most of the bird tracks and body fossils dating as far back as the Early Cretaceous are from the Northern Hemisphere, particularly from Asia,” Martin observes.

“The birds would likely have been stepping on soft sand or mud. Then the tracks may have been buried by a gentle river flow that deposited more sand or mud on top of them,” Martin elaborated.

This new evidence indicates a diverse avian presence near the South Pole around 125 million years ago. As a specialist in ichnology, Martin’s expertise lies in interpreting these ancient traces of life.

Characteristics and location

The discovered bird tracks vary in size from seven to 14 centimeters wide. This matches the size of modern-day shorebirds, such as small herons and oystercatchers. These tracks are among the largest known from the Early Cretaceous and were found in the Wonthaggi Formation, a geological site south of Melbourne.

The Wonthaggi Formation, where the tracks were located, marks a significant geological period when the supercontinent Gondwana began to fragment. This period was characterized by a polar environment with a rift valley and braided rivers. Severe winters and prolonged periods of darkness were common.

The multiple stratigraphic levels where the tracks were found suggest a recurrent presence of various bird species. This may indicate seasonal formation during polar summers. This could point to migratory patterns among these ancient birds.

Preserving the bird footprints

Martin notes the difficulties in preserving bird fossils, given their small and lightweight bone structure. This rarity makes the discovery of the Wonthaggi tracks all the more remarkable. The Wonthaggi Formation itself is known for its rich variety of polar dinosaur bones. However, bird fossils have been extremely scarce.

“Birds have such thin and tiny bones,” Martin says. “Think of the likelihood of a sparrow being preserved in the geologic record as opposed to an elephant.”

Martin and his colleagues previously discovered two 105-million-year-old bird tracks in Australia’s Eumeralla Formation, which were then the oldest known in Australia. The current discovery was initially spotted in 2020 by co-author Melissa Lowery, a local volunteer fossil hunter, renowned for her skill in finding fossil tracks.

“Melissa is incredibly skilled at finding fossil tracks,” Martin says. “Some of these tracks are subtle even for me, and I have lots of experience and training.”

Field analysis and challenges

The COVID-19 pandemic posed significant challenges, delaying field analysis until 2022. Martin, along with Patricia Vickers-Rich and Thomas Rich, both of whom have contributed significantly to the understanding of Gondwana’s biota, led the field analysis.

The detailed examination of the tracks, such as the thinness of the toes and the angles between them, was crucial in confirming their avian origin. Claudia Serrano-Brañas, a co-author and paleontologist, compared these tracks with ancient bird footprints from other parts of the world to verify their similarities.

Preservation efforts

Peter Swinkels, a co-author and expert in specimen preservation, created resin casts of these tracks. These casts not only aid in further research but also help in preserving these ephemeral geological records, which are rapidly eroding due to coastal tides and waves.

Reflecting on the transient nature of these discoveries, Martin remarks, “Seven of the tracks that Melissa found in 2020 are no longer there.” This statement underscores the urgency in documenting these rare and fleeting glimpses into our planet’s ancient past.

The discovery of these avian tracks in Southern Australia not only enhances our understanding of early bird life, but also highlights the impermanent nature of geological records.

This study is the result of collaborative efforts by an international team, including experts from Monash University and the Museums Victoria Research Institute in Australia; the Benemérita Normal School of Coahuila in Mexico; and the Smithsonian Institution.

More about birds in the Early Cretaceous

The Early Cretaceous period, spanning from approximately 145 to 100 million years ago, marked a significant era in the evolution of birds. During this time, birds diverged further from their dinosaurian ancestors, developing characteristics that defined modern avian species.

Diversity and adaptation

Birds in the Early Cretaceous showcased a remarkable diversity in form and function. This era witnessed the emergence of various bird groups, each adapting to different ecological niches.

Some developed specialized beaks and feet for different feeding strategies, while others adapted for efficient flight, demonstrating the versatility and adaptability of early birds.

Fossil records and discoveries

Fossil discoveries from this period, including the discovery discussed above, provide key insights into the evolution of birds. Notable fossils include well-preserved specimens with feathers, which help scientists understand the transition from feathered dinosaurs to modern birds.

These fossils reveal early birds’ physical characteristics, such as toothed beaks and long, bony tails, which gradually disappeared in later avian evolution.

Behavioral aspects

Behavioral aspects of Early Cretaceous birds, such as nesting habits, can be inferred from fossilized nests and eggs. These discoveries suggest that some early bird species exhibited behaviors similar to modern birds, like brooding and possibly vocal communication.

Ecological significance

Early Cretaceous birds played vital roles in their ecosystems. As insectivores, frugivores, and possibly even small carnivores, they contributed to the balance of their habitats. Their presence indicates a complex and thriving ecosystem during this period.

In summary, the Early Cretaceous period was a critical time in avian history, marked by diversification and adaptation. The fossil record of bird footprints from this era, while still incomplete, provides invaluable insights into the early stages of bird evolution, illustrating a dynamic period in the history of life on Earth.

The full study was published in PLoS ONE.

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