The discovery of 27 avian footprints alongside the southern coast of Australia, originating from the Early Cretaceous interval when Australia was linked to Antarctica, offers a brand new perspective on the early evolution of birds and potential migratory patterns
The findings, documented in PLOS ONE, current a number of the earliest definitively recognized hen tracks within the Southern Hemisphere, relationship again roughly 120 million to 128 million years.
Ancient avian tracks: Understanding the evolution of birds
“Most of the bird tracks and body fossils dating as far back as the Early Cretaceous are from the Northern Hemisphere, particularly from Asia,” says Anthony Martin, first creator of the examine and a professor in Emory University’s Department of Environmental Sciences.
“Our discovery shows that there were many birds, and a variety of them, near the South Pole about 125 million years ago.”
Martin specialises in iconology, which examines life traces like tracks, burrows, nests, and tooth marks. The collaborative group of authors includes researchers from Monash University, the Museums Victoria Research Institute in Australia, the Benemérita Normal School of Coahuila in Mexico, and the Smithsonian Institution.
Geological context of the findings
The 27 avian footprints exhibit various sizes and styles, rating among the many largest recognized from the Early Cretaceous interval. Ranging from seven to 14 centimetres in width, these dimensions intently resemble the tracks of latest shorebirds like small herons and oystercatchers.
Discovered within the Wonthaggi Formation south of Melbourne, these tracks are embedded in rocky coastal strata, marking the geological transition when the traditional supercontinent Gondwana began to fragment roughly 100 million years in the past. This fragmentation led to the separation of Australia from Antarctica.
Rare Bird fossils in Wonthaggi
During this period, the polar atmosphere was characterised by a rift valley with braided rivers. Despite the Cretaceous interval having a better imply annual air temperature than the current, the polar winters featured deep freezing temperatures and prolonged durations of darkness within the ecosystem.
The avian tracks within the Wonthaggi Formation are distributed throughout a number of stratigraphic ranges, signifying a repeated presence of various hen species. This remark hints at the potential for the tracks forming seasonally, doubtless throughout polar summers and probably alongside a migratory route.
The Wonthaggi Formation is famend for its assortment of polar dinosaur stays, with exceptionally scarce hen fossils. Within the Cretaceous strata of this formation, solely a solitary tiny hen bone, particularly a wishbone, together with a handful of feathers, has been unearthed.
“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.”
Avian identification by way of monitor options
Birds, being light-weight, have a tendency to go away minimal foot impressions. In 2013, Martin and colleagues discovered two 105-million-year-old hen tracks in Australia’s Eumeralla Formation, marking them because the oldest from Australia.
Melissa Lowery, a volunteer fossil hunter and co-author, initially recognized a number of the tracks within the recent discovery in 2020. Many tracks had been solely seen throughout low tide, and a few had been lined with marine life like algae, barnacles, and molluscs.
Challenges and insights from fieldwork
Due to COVID-19 journey restrictions in Australia, Martin needed to wait till 2022 to guide the monitor analyses on-site. He was joined by co-authors Patricia Vickers-Rich and Thomas Rich, specialists in palaeontology and vertebrate palaeontology, respectively. The couple has been actively concerned in fossil exploration and deciphering Gondwana’s biota because the Seventies within the Australian state of Victoria.
Field analyses had been additionally supported by co-authors Mike Hall, a geologist at Monash University, and Peter Swinkels, a taxidermist at Museums Victoria Research Institute specialising in preserving specimens by way of mouldings and casts.
Martin confirmed the avian id of the tracks by inspecting the thinness of the toes in regards to the monitor lengths, the broad angles between the toes, and the presence of slender, sharp claws and rear toes in a number of the tracks.
