Birds may not seem like fascinating windows into the past, but to paleontologists, our feathered friends are living relics. Birds have a direct continuum going back to the age of the dinosaurs. Many species survived, but others, such as Tyrannosaurus, went extinct in catastrophes. But why the birds were able to survive is still open for research. New research suggests that moulting patterns in certain prehistoric species controlled their survival and may have shaped modern bird biology. Birds shed their feathers in the process of replacing these precious keratin (which makes up the nails) appendages. This is the process by which chicks acquire adult feathers, much like human children lose their milk teeth. There are two types of moulting patterns in birds that should be considered. Altricial birds are born naked and are kept warm by the body temperature of their parents.
Immature birds are born with their own baby wings. They all moult regularly into adulthood, a very energy-consuming process. Also, if a bird (such as an altricial chick) moults all its feathers at once, it can make the bird vulnerable to temperature changes. It gradually loses its plumage during the moulting period, making it less protective than the species it replaces.
A recent study by Shandong Bi and Jingmai O'Connor examined chick feathers preserved in amber. The Field Museum in Chicago called these incredibly rare finds and "the first definitive fossil evidence of moulting in hatchlings." The bird was probably an early social enantiornithine bird. Interestingly, however, feathers tell a slightly different story. "This specimen shows a really strange combination of presocial and altruistic traits," says O'Connor. "All the feathers on the body are basically at exactly the same stage of development, which means they all started growing at or near the same time." An asteroid impact would have caused the planet's temperature to plummet and its resources to become scarce. So not only did these birds need more energy to maintain their body temperature, they also didn't have the resources to meet that need. "