Ancient Aussie Footprints Uncover Earliest Reptile Discovery

Seventeen fossilized footprints found in a sandstone slab in southeastern Australia, dating back approximately 355 million years, are challenging previously held beliefs about the evolution of land vertebrates. These discoveries suggest that reptiles emerged significantly earlier than once thought.

These ancient footprints, likely created on a muddy riverbank, consist of two distinct trackways and one solitary print, all showcasing key characteristics associated with reptile movements, including shape, toe length, and claw marks. Researchers believe these prints were made by a reptile whose body size was comparable to that of modern lizards.

This find indicates that reptiles existed around 35 million years earlier than previously established timelines, suggesting a much faster pace in the evolution of land vertebrates than envisioned.

“This is groundbreaking research,” stated paleontologist Per Ahlberg from the University of Uppsala in Sweden, who led the study published in the journal Nature.

The sandstone slab containing the footprints measures roughly 14 inches (35 cm) across and was discovered along the banks of the Broken River, close to the town of Barjarg in Victoria.

The history of land vertebrates began with fish venturing onto land—a pivotal moment in the evolution of life on Earth. These early tetrapods, meaning “four-footed,” were the ancestors of today’s amphibians, reptiles, mammals, and birds. The oldest fossil evidence of these initial tetrapods, which led an amphibious lifestyle, was found in Poland and dates back about 390 million years.

These ancestral creatures eventually branched into two primary lineages—one leading to modern amphibians and the other to amniotes, a group that includes reptiles, mammals, and birds. Amniotes were the first vertebrates to lay eggs on land, freeing them from the constraints of aquatic environments. This group split further into two lineages, leading respectively to reptiles and mammals, with birds evolving much later from reptilian ancestors.

The Australian footprints measure about 1 to 1.5 inches (3 to 4 cm) in length and are believed to have been made by three individuals of the same species, lacking any signs of tail or body drag. Although no skeletal remains were found, the prints provide insights into the physical appearance of the reptiles that created them.

“The feet resemble those of lizards, and the distance between the hip and shoulder appears to be about 17 cm (6.7 inches). While we can’t determine the shape of the head, length of the neck, or tail, we can infer that if it maintained lizard-like proportions, its total length might have ranged from 60 cm to 80 cm (24 to 32 inches),” Ahlberg explained.

“Overall, it’s reasonable to think of it as ‘lizard-like,’ as modern lizards retain a form closest to this ancestral body shape,” he added.

The relatively small size of these early reptiles stands in stark contrast to some of their later descendants, such as dinosaurs.

This reptile was likely a carnivore since herbivorous reptiles did not emerge until later in their evolutionary history. Herbivorous reptiles generally have larger, bulkier bodies, while this species is characterized by its slender toes and agile build, indicating a predatory lifestyle, according to Ahlberg.

The researchers also identified similar fossilized footprints of reptiles in Poland that date back 327 million years, which, like those in Australia, predate the earliest known skeletal fossils of reptiles—Hylonomus—found in Canada, which is around 320 million years old.

The reptile that made the Australian footprints thrived during the Carboniferous Period, a time when global temperatures mirrored those of today, featuring polar ice and warm equatorial regions. At that time, Australia was part of the ancient supercontinent Gondwana, located at the southern edge of the tropics and home to vast forests, some containing gigantic clubmoss trees.

“These tracks were likely created near the banks of a significant river, inhabited by a variety of large fish,” Ahlberg noted.