Article by: Charles Fatima, on 06 July 2023, at 04:11 am PDT

The remarkable phenomenon of molting, observed in both fossilized feathers and modern birds, holds vital clues to the survival strategies of ancient avian species during the extinction of dinosaurs. Feathers, composed of keratin, serve birds in numerous ways, from flight and protection to attracting mates and temperature regulation. However, maintaining these complex structures requires periodic shedding and regrowth. Scientists delving into the evolution of molting have unearthed intriguing findings that shed light on how molting patterns influenced the fate of prehistoric birds amidst mass extinctions.

In a ground-breaking study published in May 2023 in the journal Cretaceous Research, a team of researchers made an astonishing discovery—a cluster of preserved feathers trapped in amber, belonging to a 99-million-year-old baby bird. These remarkably preserved feathers provided the first direct fossil evidence of juvenile molting, revealing a fascinating combination of precocial and altricial characteristics unseen in today's avian species. By studying the complexities of molting patterns in ancient birds, scientists aim to decipher the evolutionary pathways and survival mechanisms that shaped diverse bird lineages.

Jingmai O'Connor, an associate curator of fossil reptiles at the Field Museum, emphasizes the pivotal role of molting in understanding avian evolution and survival dynamics. By unraveling the variations in molting across different bird groups, researchers gain insights into the diverse strategies adopted by bird clades to ensure their survival. O'Connor's prior research has unveiled the high precociality of the Enantiornithines, an extinct group that likely encompassed the baby bird with preserved feathers.

The challenges faced by precocial baby birds—those born with feathers and relatively self-sufficient—in maintaining body heat while undergoing rapid molts could have contributed to the extinction of the Enantiornithines. O'Connor proposes that catastrophic events, such as asteroid impacts leading to global cooling and resource scarcity, placed additional energy demands on these birds to stay warm. Ultimately, the combination of harsh environmental conditions and limited resources may have played a role in their extinction alongside other non-avian dinosaurs.

In a complementary study published on July 3 in Communications Biology, O'Connor and Yosef Kiat, a postdoctoral researcher at the Field Museum, investigated molting patterns in modern birds to shed light on the early stages of molting evolution. While most modern birds undergo sequential molts, gradually replacing a few feathers at a time over several weeks, simultaneous molts, characterized by the shedding and regrowth of all flight feathers within a shorter timeframe, are rare and typically observed in aquatic species like ducks that do not heavily rely on flight for survival.

To understand the scarcity of evidence for molting in fossil birds and feathered dinosaurs, the researchers analyzed the extensive collection of modern bird skins at the Field Museum. The results revealed a significant disparity, with simultaneous molters being conspicuously underrepresented in the fossil record compared to sequentially molting birds. Statistical analysis inferred that fossil birds likely molted less frequently or exhibited irregular molting patterns that deviated from the annual molt cycles observed in most contemporary birds.

The combined insights garnered from the study of ancient feathers preserved in amber and modern bird molting patterns provide compelling evidence of the divergent molting strategies between ancient and present-day avian species. Molting emerges as a crucial factor in understanding the survival of various dinosaur groups during mass extinction events. While the survival of crown birds, encompassing modern avian species, can be attributed to a multitude of characteristics, molt appears to have played a significant role in determining the fates of different dinosaur lineages.