The guttural squawk of the spooked Great Blue Heron as he arose from the shore of the brackish swamp took me back 200 million years, until my ringing cell phone jarred me back to the present. I suspect that the heron somewhat resembles its Mesozoic ancestors; large bird with wide wingspan and slow, flapping, straight line flight. But who knows for sure? The fossil record is spotty and the origin of birds has been hotly debated in academia for centuries. This is not a “settled science”.
Remember the Genesis story. Then God said, “Let the waters swarm with fish and other life. Let the skies be filled with the birds of every kind, each producing offspring of the same kind”…And God saw that it was good. It was and is very good.
In the 18th century some thought that fish and their scales were the precursor of the birds and their feathers, but by the mid 19th century scientists began to notice the many reptilian characteristics of birds. Note the common three fingers hidden by the wing, and just substitute the heavy teeth with a lighter beak, add some feathers, and you have a bird. But its not that easy.
A big break came in 1861, just two years after the publication of the “Origin of Species” by Darwin, when Archaeopteryx (Greek for “ancient wing”) was uncovered in a limestone quarry in Bavaria. This 150 million year old Crow-sized fossil had the tail, spine, and claws of a reptile, but the wishbone and feathers of a bird. Was this the transitional link? Let the debate begin.
The fossilization of birds is a very rare event. Birds have thin, hollow bones and delicate feathers. For a fossil to form the sediment must be oxygen-free and very fine in order to bring out the subtle detail of soft tissues and feathers. That’s why Archaeopteryx was so exciting. Later, in 1926 Heilmann published “The Origin of Birds” which suggested that birds and dinosaurs were related and shared a common bipedal reptilian ancestor 230 million years ago, but birds did not evolve from dinosaurs directly.
Feathers evolved long before flight so clearly they must have offered some other survival advantage. Many of the early feathered dinosaurs were much too heavy for flight and lacked other skeletal features that flight required. The symmetrical dinosaur feather (birds have an asymmetric feather with a hollow core) were more likely used for insulation or for courtship display. What female dino could possibly resist a male feather dance, or was it the female doing the dancing? We’ll never know.
Luckily there were numerous fossil discoveries in China and Spain in the late 20th century that shed new light on the origin question. As a result, the current consensus is that birds did indeed evolve directly from Theropod dinosaurs, a group that includes the ferocious Tyrannosaurus Rex, but also a group of smaller, lighter, bipedal, raptor-like “dromeosaurs” that share many characteristics with early birds.
The early to mid Cenozoic Era (37 to 65 million years ago) was a heyday for the birds. The evolution of angiosperms (flowers) and grasses, and the mild climate were ideal. Its been estimated that since their origin in the Mesozoic Era the Earth has hosted 150 thousand different species of birds. There were two mass extinctions, however, that severely thinned the ranks. The earlier was in the Cretaceous Period and took out many groups of toothed, aquatic birds along with all the dinosaurs. The latter was in the Pleistocene epoch, 1.5 million years ago, a time of great climate upheaval with ice and glaciers covering vast areas of North America. Of the 21 thousand bird species present at the outset of that epoch, only 10 thousand remain today.
By 20 million years ago most of the modern bird families and genera had appeared, but what are the most ancient birds? Which are the true “early birds” that have survived the longest? Only two major bird groups date back to the late Cretaceous Period in the Mesozoic Era, 65+ million years ago. They are the Suborder Charadrii (shorebirds and gulls), and the Super Family Procellarioidea (albatrosses and petrels). The others all came later onto the scene.
There’s something about the dinosaurs that fascinate children, including me. They learn the long names in kindergarten and play with their plastic models. Maybe its their size or power, or maybe its because they ruled the Earth for so long and then disappeared so quickly and mysteriously. Was it a comet strike or something else? In any case, I’m so happy that some of their feathered offspring survived and continue to bring us newcomers, Homo sapiens, much pleasure today in the Cenozoic Era, Quaternary Period, and Holocene Epoch.