In addition to fossils, petrified footprints can also reveal a lot about the prehistoric world. In southern Australia, researchers have now discovered some of the oldest bird tracks known to date in this part of the world. Such finds have so far been rare on southern continents that emerged from the Gondwana landmass. The footprints that have now been discovered are at least 120 million years old and indicate that various types of birds already populated the area back then - possibly as a seasonal stop on their migration.
In the Northern Hemisphere, fossil evidence of birds extends back to the Upper Jurassic, more than 150 million years ago. On the other hand, for southern continents, which once emerged from the land mass of the original Gondwana, it is unclear how and when birds spread there. The oldest known fossils in the shape of a bird bone and a feather come from the Wonthaggi Formation in Victoria, Australia and are estimated to be around 120 million years old.
Diverse footprints
“Given the paucity of Mesozoic bird fossils, we have little clues as to when birds arose in Australia and most other Gondwanan landmasses, let alone how they interacted with their environment,” writes a team led by Anthony Martin of Emory University in Atlanta, Georgia. But during excavation work between 2020 and 2022, co-author Melissa Lowery from Monash University in Victoria discovered further evidence of Cretaceous birds. In the Wonthaggi Formation, from which the oldest bird body fossils to date also come, she came across several fossilized footprints that had apparently been left by various bird species more than 120 million years ago.
Further investigation by the team revealed a total of 27 footprints. “The identity of these tracks as bird tracks is confirmed by their three-toed shape, the thin toes in relation to the track length, the wide spread angles and the sharp claws,” explain the researchers. Since the individual tracks have significantly different shapes and sizes, Martin and his team assume that they were made by several different species of birds. Some of these are among the largest known from the Early Cretaceous.
Prehistoric migratory birds?
“Although there are no connected tracks, the close spacing and similar orientation of the tracks on some strata surfaces suggest social coexistence,” the team writes. At the time the bird tracks are from, the area experienced regular seasonal flooding. “Because we discovered the bird tracks in several stratigraphic layers of the Wonthaggi Formation, we conclude that the birds repeatedly visited the region,” explain Martin and his colleagues. “The tracks were probably created seasonally during the polar summers, which could also indicate migration of these early birds.”
The tracks provide insights into the early history, biodiversity and adaptations of birds in Gondwana. Although no similarly old traces are known from other parts of the former Gondwana, paleontologists assume that the occurrence of the birds at that time was not only limited to the region around the Wonthaggi Formation. “We hope that our discovery of trace fossils will inspire other researchers to search for and find additional Early Cretaceous bird tracks in other regions of the Southern Hemisphere,” the team said.
Source: Anthony Martin (Emory University, Atlanta, Georgia, USA) et al., PLoS ONE, doi: 10.1371/journal.pone.0293308