Sections
The age of dinosaurs wasn’t just the golden age of giants with thorns and teeth. Birds were as important a component of the dinosaur saga as stegosaurus, and a new discovery among the rocks of South Australia indicates that one of the world’s oldest avian traditions likely dates back more than 120 million years. years. Fossil footprints of hungry birds likely document one of Earth’s earliest bird migrations, in which feathered flying birds timed their stopover in what was then part of the South Pole to take advantage of excess food from fluffy invertebrates during the hot season.
Researchers on Wednesday described fossilized footprints that help tell the long story of bird migration in PLOS One. The full significance of those lines wasn’t entirely clear when study co-author Melissa Lowery of Monash University in Australia discovered them in 2020. She and her colleagues sent photographs to study co-author Anthony Martin, a paleontologist at Emory University, who recalls, “My first impression of the smaller footprints was that they came from small theropod and ornithopod dinosaurs,” or non-avian dinosaurs. But when Australia lifted its Covid-19 ban and Martin was able to stop to see the footprints himself, it temporarily became clear that the Cretaceous fossils were formed through other creatures. The footprints were left through prehistoric birds, the oldest bird tracks ever discovered in Australia.
“The lines tested by the authors are truly remarkable,” says paleontologist Carolina Acosta Hospitaleche of the Argentine National University of La Plata, who was not involved in the new study. “This is a vital discovery for fossil studies and provides valuable data on the early stages of avian evolution. “
According to Martin, distinguishing bird tracks from those of small non-bird dinosaurs is a tricky task. After all, birds are dinosaurs that usually walk on 3 feet, with a fourth toe on the top of their foot, just like many of their relatives. However, researchers can distinguish them in several ways. Mesozoic bird tracks are small, less than six inches long and slender, with three legs that form giant angles that exceed 90 degrees. The footprints discovered in Australia meet those and other requirements, Martin says, “and I’m pleased to say that those Early Cretaceous footprints passed the test with flying colors. “
The 27 footprints at the South Australian site were left more than 120 million years ago. At the time, Australia was located further south and was still attached to Antarctica. The ancient sediments constitute a polar environment that would have been dark and bloodless for much of the time. the year. And yet, footprints show that at least 8 other Cretaceous bird bureaucracies gave up over the years. Something must have drawn them to this place.
“The bird tracks were not only numerous, but also varied in length and shape,” says Martin, “and may have been discovered in other rock levels. ” Obviously, several species of Cretaceous birds have returned to the same position over the years. . According to Martin, discovered at a site on Cretaceous Earth, “a variety of birds probably visited the floodplains of polar rivers during the summers, after darkness, bloodless winters and spring thaws followed the floods. ” The cyclical nature of those seasonal adjustments helped create situations where footprints may simply be left in the sediment and then temporarily covered with more sediment, year after year.
Like fashionable migratory birds, Cretaceous birds probably traveled in search of food. Bird tracks aren’t the only fossil lines found in rocks. The same layers show burrows created by tiny creatures that lived along the coast. “The footprints suggest that those early risers were catching worms, insects, or other invertebrates that were active in polar summers,” Martin says. The birds stopped when the old buffet was well stocked.
More evidence will be needed to prove the concept that birds migrated seasonally to coasts along the South Pole, Acosta Hospitaleche says, but the evidence so far is compelling. Cretaceous birds probably behaved with fashionable species that take advantage of the same seasonal changes. “Migration to and from such excessive habitats throughout the seasons is really plausible,” says paleontologist Benjamin Kear of Uppsala University in Sweden, who was not involved in the new study.
Most surprisingly, the footprints are older than any fossil of bird bodies, such as bones or feathers, discovered in Australia or ancient Antarctica. Footprints can help paleontologists identify which species are in a specific domain or when they began to move into a new domain. , even when skeletal remains are scarce. ” At least those footprints show that birds were able to thrive in polar environments during the age of the dinosaurs,” Kear says.
Martin didn’t expect to find a reflection of the modern world in such ancient rocks. The first birds evolved about 150 million years ago, towards the end of the Jurassic, in the Northern Hemisphere. About 30 million years later, according to fossil records, birds had spread across the planet. “These footprints tell us that birds probably diversified and flew to widely separated land masses around the world some time after their origin,” Martin says, evolving to move with the ancient seasons.
Get the latest science delivered to your inbox.