How Early Were the Birds?
Exploring the BirdDinosaur Nexus by David Wiedenfeld
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or more than 100 years starting in the 1860s, the famous Archaeopteryx lithographica was thought to be the earliest bird, or at least bird-like dinosaur. That’s because Archaeopteryx fossils showed something never seen before: feathers. This crow-sized creature with both bird and dinosaur traits lived during the Jurassic Period about 150 million years ago (MYA). That was a long time back, but the origin of birds was probably millions of years before then. It can be hard to decide, however, what was a bird and what wasn’t. That’s because many dinosaur lineages exhibited such bird-like characteristics as walking on two legs or having a kind of beak, although with teeth, but many of these creatures probably weren’t really birds. There is now scientific consensus that birds are “living dinosaurs” that evolved from a branch of dinosaur ancestors, but there is no distinct break that we can point to and say, “Now, these are birds, and these aren’t.” Instead, we see a gradual accumulation of bird-like characteristics, including feathers, over time. (And, as just mentioned, there were also lineages with bird-like characteristics that never became birds.) Millions of years before Archaeopteryx, dinosaurs like the squat, turkey-sized herbivore called Kulindadromeus zabaikalicus began to show some evidence of something that would eventually become feathers. Kulindadromeus and its relatives, and maybe even many other kinds of dinosaurs, had a type of proto-feathers: a covering of thread- or hair-like filaments that resemble some kinds of bird down. Such fine filaments were very different from
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B I R D CO N S E R V A TI ON | SU M M ER/ FA L L 2021
the plumes seen on Archaeopteryx, and likely served as insulation rather than aiding in flight. Feathers do seem to make the bird, though: In modern times, we don’t know of any animals that have feathers that aren’t birds. This is what made Archaeopteryx such a key discovery for 19th-century paleontologists. Feathers, of course, usually do not preserve well as fossils; hard structures like bones are much better preserved. Feathers are only preserved as fossils when they are covered very quickly and gently by fine sediments that harden to stone without being further disturbed, saving their imprint. However, in the last 30 years, paleontologists have been investigating rock formations, especially in Asia and South America but also North America, that do preserve these kinds of impressions. There have been many recent discoveries that tell us more about the early birds and what they were like. Many of these recently found fossils show evidence of feathers, from early fluff-like feathers that resemble those found on modern, flightless kiwis to fully developed ones, as we think of a modern bird’s flight feathers. Some of these fossils have greatly increased our knowledge of what birds looked like, even down to their color patterns.
