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.

A new study challenges the view that leprosy is a disease that was introduced into the Americas during European colonization. It reports that a strain of leprosy-causing mycobacterium, Mycobacterium lepromatosis, that was only discovered in recent years infected humans in the Americas longer ago – before European contact. The findings reshape current views of leprosy in the Americas and provide insights into the long-term interactions between humans and infectious diseases. There are two known mycobacteria that cause leprosy: Mycobacterium leprae and Mycobacterium lepromatosis. The former seems to have arrived in the Americas with European colonization and the latter was discovered in 2008 – and mostly reported in the Americas. To date, the only genomic data available from M. lepromatosis was obtained from three human samples from patients of Mexican origin and from seven red squirrels from Great Britain/Ireland, thereby limiting current understanding of the genetic diversity and history of the species. Here, Maria Lopopolo and colleagues sought to investigate the contemporary distribution and diversity of M. lepromatosis. They studied contemporary M. lepromatosis sequences, where data was available. To clarify the history and past prevalence of M. lepromatosis in the Americas, they also studied ancient DNA datasets from pre-European contact Ancestors from the Americas. Notably, the screening of pre-contact Ancestors uncovered three samples positive for M. lepromatosis in locations spanning the length of the Americas. “While our findings do not challenge the introduction of M. leprae leprosy into the Americas by European and African populations,” say the authors, “they reveal that M. lepromatosis was already circulating within human populations across the continent several centuries before the European arrival.”

In a Perspective, Mark Hanson and Peter Gluckman explore how maternal stress, caregiving quality, and early environmental conditions can shape the development of executive functions and emotional regulation in children, and how these factors contribute to the emergence of anxiety disorders in young people. Mounting evidence reveals a significant rise in anxiety disorders among adolescents ages 12 to 19, especially in developing countries like the United States, which cannot be fully explained by contemporary stressful events like the COVID-19 pandemic. This pattern suggests that broader longer-term societal or developmental factors are driving the growing prevalence of adolescent anxiety. Here, Hanson and Gluckman highlight how environmental conditions in the earliest stages of life – beginning even before birth – can significantly shape a child’s developing brain, particularly the systems responsible for emotional regulation and executive functioning. According to the authors, these early cues may "prepare" children for adversity, but if the anticipated threats never fully materialize as they grow, such heightened emotional responses may lead to anxiety disorders, especially in adolescence. This mismatch is further compounded by the rapid and dynamic social and technological changes young people now face. “Societies face an emerging burden of mental health issues, especially in young people. Although appropriate interventions are needed to help those already affected, preventative approaches are also critical,” write Hanson and Gluckman. “Solutions will need to adopt a lifecourse perspective, involving more cohesive thinking about parental and caregiver support and the early childhood years by policymakers across health, education, and social welfare."