As heat waves shimmer in the air, a truck barrels down a dirty desert road in southern Utah’s vast Grand Staircase-Escalante National Monument. Inside, two men—a paleontologist and his graduate assistant—speed through canyons and along cliffs toward a plateau up ahead. In a swirling cloud of dust, the truck bounces to a stop on a hill dotted with sagebrush. Two modern-day dinosaur hunters set off on a small foot path into the high desert. Their quarry? Fossilized eggs! Tyrannosaurus rex was one of the largest carnivores of all time. Standing 15 feet high, about 40 feet long and weighing in at roughly six tons, this monster dominated its environment. Did you know that T. rex hatchlings were fluffy and gangly, more like turkeys than the massive killing machines they grew up to be? Turns out, the similarity to young birds is more than chance; they share a common family tree. So, the next time you wish to see a dinosaur in the flesh, look no further than the crow eyeing your French fries at the park or the nearest pigeon pecking at crumbs on the sidewalk.
Today, there are some 10,000 bird species worldwide. They may be as tiny as a hummingbird or as large as an ostrich; they may soar like an eagle or dive like a penguin but they all can trace their origins to a bipedal, mostly meat-eating group of dinosaurs called theropods that first appeared around 231 million years ago, during the late Triassic Period.
If you look closely, and pay attention to details, you can see the connection in some birds more than others. For example, when you gaze upon the face of the bald eagle, what do you see? A curved, rapier-like beak; serious, piercing eyes designed to locate prey; long, sharp talons designed for grasping and holding, and scaly skin on legs and feet. You can also notice these features in somewhat less exaggerated manner on a barnyard rooster. Compare the upright skeletons of the eagle and rooster to the T. rex and the resemblance is uncanny. Is it really that much of a leap—to imagine a velociraptor standing before you? And these are only birds common to our area. The Cassowary, native to Australia, is a large flightless bird that can grow almost 6 feet tall. With a large crest on their head and blue skin, they look like they walked right out of a time machine! When threatened, these new-age dinosaurs will rear up and jab their attacker with frightening precision.
Historically, the idea that birds are descended from dinosaurs has been a contentious topic within evolutionary biology. But today only a few scientists still dispute the dinosaurian origin of birds—even then, the supposition is that birds came from other reptiles besides dinosaurs. The search for truth really got started shortly after the 1859 publication of Darwin’s on the Origin of Species. In 1860, a fossilized feather was discovered in limestone in Germany, and the race was on! Then in 1861, the earliest known bird (Archaeopteryx—150 million years old) was uncovered there too. The creature weighed around 2 lbs. and measured 20 inches long. Fossil evidence showed it had plumage on its tail and body. The shape of its forelimbs and feathers suggested it was capable of powered flight. Unlike birds today, Archaeopteryx had claw-like fingers at the tips of its wings.
Investigations, studies and speculation continued on for more than another hundred years. In the 1970’s, paleontologists noticed that Archaeopteryx shared unique features with small carnivorous dinosaurs (theropods). In the 1980’s, a new methodology—called cladistics—was applied to dinosaurs for the first time. Cladistics is an exact method of arranging species based strictly on their evolutionary relationships, which are calculated by determining the evolutionary tree implying the least number of changes in their anatomical characteristics. Morphological data is translated into numbers that are then processed by algorithms to pinpoint how animals are related. This new methodology showed unequivocally that birds were a derived group of theropod dinosaurs.
Okay, fine. I know what you’re thinking. Wouldn’t alligators and crocodiles make a neater fit? While they most look the part, they actually evolved separately from a different common ancestor (4-legged Archosaur), making crocodilians more like cousins than siblings. But dinosaurs are so different from modern-day birds, you say. Really? Let’s put on our paleontological hats and see what evidence we can find:
Lungs. Large meat-eating dinosaurs had a complex system of air sacs similar to those found in modern birds, according to an investigation led by Patrick M. O’Connor of Ohio University. In theropod dinosaurs flexible soft tissue air sacs likely pumped air through the stiff lungs, as is the case in birds. “What was once formally considered unique to birds was present in some form in the ancestors of birds”, O’Connor said.
Heart. While birds and crocodilians are the closest living relative of dinosaurs, did you know both of these modern-day species have four-chambered hearts (albeit modified in crocodilians)? This implies dinosaurs probably had them as well.
Gizzard Stones. Dinosaurs had gizzard stones, just like birds do today. These stones are swallowed by animals to aid digestion and break down food and hard fibers once they enter the stomach.
Feathers. Small theropods developed short, hair-like feathers that grew on their heads, necks, and bodies for insulation. Our famous Archaeopteryx had vane-like feathers with well-organized barbs, locked together by barbules. This is identical to the feather structure in living birds.
Scales. Not only do birds have scaly feet but scientists have discovered that the tissues used to produce scales in reptiles are similar to those that produce feathers in birds.
Molecular Evidence. Dr. Mary Higby Schweitzer and her team discovered (2005) flexible material resembling actual soft tissue inside a 68-million-year-old Tyrannosaurus rex leg bone from Montana. The collagen obtained from the bone fragments compared with collagen data from chickens suggested that older theropods were closely related to birds today. The soft tissue allowed a molecular comparison of cellular anatomy and protein sequencing of collagen tissue, published in 2007, both of which indicated that T. rex and birds are more closely related to each other than either is to the Alligator.
The transition was most probably an ugly one. Several hundred million years ago, huge and terrifying new life forms took to the air. With wings of skin, stretched between claws and the flanks of their bodies, great flying dinosaurs like the Pterosaurs dominated the skies. After the catastrophe that wiped out the dinosaurs, the evolution of birds really took off. During a time when mammals were still quite small, huge flightless “terror-birds” stalked the land while mighty vultures cruised the skies. Birds took total command of the skies and effectively ruled the planet.
With the power of flight, birds travelled further and wider in search of food and were able to live in protected places where other creatures could not go. Millions of years of evolution have refined bird species to better fit their environment and pre-programmed them to feed, migrate, nest and breed in their own unique ways.
The arrival of mankind marked a dark time for birds. Through habitat destruction, hunting, introduction of invasive species and pollution we have threatened the life of birds world-wide. The most egregious bird extinction ever has been the Passenger Pigeon. There was a time in colonial days when the population of Passenger Pigeons was so great that huge overflying flocks could darken the sky. Over time, European colonists cut down the beech forests they depended on for food, then slaughtered them for their own table. The last wild pigeon was shot from the sky in 1900; the last captive bird—Martha—died in the Cincinnati Zoo in 1914.
Despite the challenges, birds remain adaptable. Falcons can be seen diving down the sides of skyscrapers in large cities, picking off smaller birds. Black Vultures often hang out on tall building ledges and spend hours basking in front of warm exhausts from air-conditioning units. Food is plentiful, just a flap and a glide away from urban garbage. In some cities, like London, pigeons outnumber human beings! Bird lovers across the globe are growing. Perhaps there is hope.
It has taken us a very long time to discover the ancestry of birds, and this knowledge begs the question: What will be their future? All I know is this: birds have been around a lot longer than mankind and, unlike us, they show no tendencies to destroy their own species. And then there’s this: At the end of the first Jurassic Park film there’s a scene where the survivors, having narrowly escaped being killed by dinosaurs, are leaving Isla Nublar by helicopter. The main character looks out the chopper window and his gaze settles on a flying flock of Brown Pelicans. The camera lingers on the pelicans, and without a word, the message is clear: They’re still here. We still have living dinosaurs, but today we call them birds!
By Larry Gfeller