How Did Some Birds Survive Extinction 66 Million Years Ago?

Feduccia

The dinosaurs disappeared 66 million years ago. Did every single one of them go extinct? Not exactly. Some of them did indeed survive and are still present today. We even encounter them in our daily lives. These survivors are none other than birds.

Yet, not all species of avian dinosaurs managed to survive the immense biological upheaval of that time. Only a specific group achieved this remarkable feat. This has been a mystery that has captivated paleontologists for a long time. However, some researchers may have unraveled the solution to this enigma. It appears that the key might lie in the story of feathers, or more precisely, in the mechanism of feather molt.

Recent research suggests that the crucial factor determining the survival of certain species over others might be attributed to the way they molted their feathers.

Molting: An Essential Mechanism for Bird Survival

A baby dinosaur's tail is encased in amber along with ants, a beetle and plant fragments.
A baby dinosaur’s tail is encased in amber along with ants, a beetle and plant fragments. Image: Ryan McKellar, Royal Saskatchewan Museum.

Feathers stand as the unmistakable hallmark of birds across all species. Made up of keratin, akin to our hair and nails, feathers hold vital significance for birds, enabling them to fly, swim, camouflage, attract mates, shield themselves from cold or sunlight, and more.

Despite their delicate nature, feathers serve myriad purposes, yet once damaged, they cannot be restored. To uphold the integrity of their plumage and ensure survival, birds have evolved a replacement mechanism known as molting. During growth, fledglings shed their downy feathers, transitioning to adult plumage. Feathers are then periodically renewed, typically once a year. Hence, the molting process assumes exceptional importance for avian creatures. But did this same characteristic apply to birds of the Cretaceous era?

A recent study, featured in the journal Cretaceous Research, delved into this inquiry. Researchers focused on preserved feathers found within a piece of amber. These feathers originated from a nestling that lived 99 million years ago, predating the Late Cretaceous biological crisis. By comparing the plumage evolution of this ancient juvenile bird with that of contemporary avians, scientists sought insights into the past.

Abrupt Molting or Gradual Molting?

A Young enantiornithine that lost its feathers during a sudden molt.
Feitianius is a genus of extinct birds from the Early Cretaceous of present-day China, belonging to the Enantiornithes.

Among the avian species we encounter today, certain nestling birds fall into the category of altricial species. These hatchlings enter the world devoid of feathers, rendering them inherently vulnerable. Nonetheless, this lack of plumage carries its own advantage: it facilitates the efficient transfer of parental body warmth to the offspring. This phenomenon is evident in creatures like parrots and pelicans. Moreover, such species undergo rapid and complete molts, benefiting from parental care that includes nourishment and warmth.

Conversely, there are other species classified as precocial, encompassing chicks and ducklings. These young birds emerge into the world already adorned with feathers and promptly acquire independence. To avert exposure to inclement weather and cold conditions, these precocial species do not undergo simultaneous full molts like their altricial counterparts. Instead, molting unfolds progressively, ensuring a continuous protective plumage.

Survival Is Impossible for Completely Naked and Unprotected Fledglings

Cuspirostrornis houi life restoration with ginkgo and araucaria
Life restoration of Cuspirostrisornis houi amid ginkgoes and araucaria pines. Image: Tiny Longwin.

However, the feathers encased in amber unveil an entirely distinct mechanism that diverges from the behaviors exhibited by any contemporary avian species. These feathers possess a blend of characteristics found in both precocial and altricial species. Even though the nestling associated with these feathers seems to have come from the enantiornithines, a lineage of birds that were very advanced for their age and are now extinct, all of the feathers show the same stage of development. This stage aligns more closely with the abrupt and total molt typical of altricial species.

For scientists, this could have represented a vulnerability within this significant avian group. Such susceptibility may have contributed to the extinction of enantiornithines approximately 66 million years ago. Bereft of parental assistance, juvenile enantiornithines would likely have encountered considerable challenges dealing with a complete loss of plumage in an increasingly hostile environment. Naked and defenseless fledglings would have faced an inevitable demise—an outcome fraught with certainty for a species during times of ecological upheaval.

Within the context of environmental and biological crises, only those species enjoying parental safeguarding or adopting a gradual molting strategy would have persevered. This scenario serves as yet another compelling illustration of the extraordinary forces of natural selection at play.