Two fossilized bird footprints in Australia date to more than 100 million years ago, making them the oldest known bird tracks in Australia, a researcher says. Found at a fossil-bearing site dubbed Dinosaur Cove in Victoria, the tracks were likely made by birds during the Early Cretaceous, paleontologist Anthony Martin at Emory University in Atlanta said. Martin is an expert in so-called \"trace\" fossils, which include tracks, burrows and nests. The thin-toed tracks in riverbed sandstone were likely made by two individual birds that were about the size of a great egret or a small heron, said Martin, who conducted his research with colleagues from Monash University and the Museum Victoria. Much of the rocky coastal strata of the region around Dinosaur Cove were formed in river valleys in a polar climate during the Early Cretaceous, they said. \"These tracks are evidence that we had sizeable, flying birds living alongside other kinds of dinosaurs on these polar, river floodplains, about 105 million years ago,\" Martin said. Most of what is known about early birds during the Cretaceous comes from well-preserved fossils found in northeastern China, he said. \"In contrast, the picture of early bird evolution in the Southern Hemisphere is mostly incomplete,\" Martin said, \"but with these tracks, it just got a little better.\"