The modern birds originate from a side branch of the dinosaur evolutionary tree; most paleontologists harbor no doubt about this. Their closest living relatives are crocodiles, and their immediate ancestors were likely small, tree-dwelling predatory dinosaurs from the Maniraptora group. The timing of the appearance of beings that can be considered true birds is a matter of debate.
The oldest known fossils deserving of this designation come from deposits dating back approximately 150 million years in the Upper Jurassic. Examples from the Chinese Tiaojishan Formation are recognized, with some specimens even dated to around 160 million years ago.
Hardly any Fossils
Until representatives of the newly emerged branch on the tree of life conquered the Southern Hemisphere of our planet, some time must have passed. There are very few corresponding ancient early bird fossils from the southern continents, which were once part of the Gondwana landmass. Therefore, the picture of the distribution of the first birds is also extremely incomplete.
However, researchers have now literally discovered traces indicating the existence of birds in the southern polar regions already 120 million years ago: A team led by Anthony Martin from Emory University (USA) reports in the journal Plos One on the discovery of a series of bird footprints from the Early Cretaceous (129 to 120 million years old) Wonthaggi Formation in Victoria, Australia.
The paleontologists described 27 individual traces with characteristics exclusively known from birds. They are between seven and 14 centimeters wide, similar to the tracks of contemporary coastal birds. The varying sizes and shapes of these imprints even suggest the presence of different bird species. Some of these could belong to the largest species known from the Cretaceous period.
These tracks have been preserved in several stratigraphic layers of an ancient polar floodplain. This could imply that these birds seasonally visited the area at that time, possibly as part of a migratory route, according to the researchers.
Were There More?
Apart from a few fossilized bones and feathers, these are the oldest known evidence of birds in Australia or any other part of ancient Gondwana. Furthermore, these tracks also represent the earliest indications that birds have ventured into polar regions. Whether these bird tracks are mere random exceptions or indicative of a denser bird population in Gondwana remains open to interpretation.
“Nevertheless, we hope that our discovery of trace fossils inspires other researchers to search for additional bird tracks from the early Cretaceous period elsewhere in the Southern Hemisphere,” stated Martin.