A collection of fossils discovered in northern Alaska shows that birds were nesting in harsh Arctic environments as early as 72.8 million years ago. The fossil assemblage, uncovered from the Late Cretaceous Prince Creek Formation in Alaska, includes a diverse group of ornithurine birds – relatives of modern species – along with rare remains of embryos and hatchlings. These findings suggest that some of the earliest modern birds were already adapted to the extreme seasonal conditions of the ancient Arctic, offering new insights into how modern birds came to thrive in polar ecosystems. Breeding in polar ecosystems presents both opportunities and formidable challenges for over 250 modern bird species. Some, like the Arctic tern, undertake extreme migrations between the poles, while others, such as the Svalbard rock ptarmigan, remain year-round in the Arctic, enduring harsh winters and prolonged darkness. Birds nest in these challenging environments to take advantage of short but highly productive summers, which offer abundant food and continuous daylight with reduced predation risk. Despite making up a small fraction of global bird diversity, Arctic bird populations can be immense and play crucial ecological roles. Understanding how birds came to occupy these habitats is key to understanding polar ecosystem evolution and functioning. However, bird fossils from polar regions – particularly those representing early lineages – are rare.
Here, Lauren Wilson and colleagues describe a rich assemblage of fossil birds from northern Alaska's Late Cretaceous Prince Creek Formation, dating to about 72.8 million years ago and located near the ancient North Pole. The fossils include a diverse array of ornithurine birds, including Ichthyornithes, Hesperornithes, and the earliest modern birds, Neornithes. Moreover, Wilson et al. identified exceptionally well-preserved perinatal (embryos or hatchlings) remains within the assemblage, marking the earliest known evidence of bird nesting in a polar ecosystem. According to the authors, several skeletal features – such as toothless jaws, specialized coracoid structures, and fused leg bones – suggest some specimens may lie near or within the crown group of modern birds, potentially related to early waterfowl. In contrast to slower-developing enantiornithine birds, which appear absent from these high latitudes, and coexisting polar-adapted dinosaurs, the authors argue that ornithurines were better suited to either overwintering or migration, which may have helped them survive the end-Cretaceous extinction and later diversify into modern birds.
