When it was first discovered in Germany in 1861, Archaeopteryx was hailed as the missing link between birds and dinosaurs and proof for the theory of evolution. This raven-sized animal lived about 150 million years ago and had feathers identical to that of modern flying birds. But Archaeopteryx also had sharp teeth, a long bony tail and clawed fingers.
At 7 feet long and 3 feet tall, Beipiaosaurus is one of the largest known feathered theropods the group of swift upright dinosaurs from birds are thought to be descended. For a long time, scientists didn't know how to classify Beipiaosaurus because it shared characteristics more commonly found among plant eating dinosaurs. It lived about 125 million years ago and had a toothless beak, cheek teeth that it used to chew plants and the beginnings of a bulging pot belly. But theropods are the only group of dinosaurs so far known to have feathers, and many scientists take Beipiaosaurus' feathers as evidence for it being a theropod.
Caudipteryx was a peacock-sized theropod that lived about 125 million years ago. And just like a peacock, it had long plumed tail-feathers that it may have fanned out for display. Caudipteryx also had down feathers covering most of its body that helped to keep it warm.
Coelophysis was a small, compact dinosaur that lived about 210 million years ago. It was a quick and agile hunter that had hollow bones and a hole-ridden skull, which helped to reduce its weight and increase its speed. Some fossils have been found with other small Coelophysis bones inside, and at first, it was thought that Coelophysis might have given birth to live young. It is now believed, however, that it was probably a cannibal that occasionally devoured its own young.
Compsognathus is one of the smallest dinosaurs ever discovered. It lived about 150 million years ago and was possibly an early relative of Archaeopteryx. Compsognathus had long legs, hollow bones and a long rigid tail that it used to balance itself while chasing down quick-footed prey.
About the size of a crow, Confuciusornis is the earliest known bird to have a true beak. It lived about 10 to 15 million years after Archaeopteryx, but like its early ancestor, it still had clawed fingers. Males were typically larger than females and sported long, narrow tail feathers that they may have used to attract mates. Some scientists question whether Confuciusornis was a direct ancestor of modern birds. They propose instead that it was a cousin that early on went its own separate way.
This early cousin of Tyrannosaurus rex lived about 130 million years ago and was covered in hairlike protofeathers, which are precursors to the feathers of modern birds. It is named after the mythical Chinese Emperor dragon, Dilong, and from the fact that it was "paradoxically," small and feathered. The feathers were probably used for warmth, and scientists suspect that juvenile T-rexes might also have had feathers, and that the feathers were shed as the animal matured.
Dromaeosaurus was a small, fast-moving predator that lived about 170 million years ago. It was about 6 feet long and was a dromaeosaurid, the family of dinosaurs that also includes Velociraptor. It had excellent vision, thanks to its large eyes, and scientists think that it also had a strong sense of smell and good hearing. Dromaeosaurus teeth have been found among the fossils of much larger animals, leading some scientists to suspect that it may have hunted in packs. It is also possible that Dromaeosaurus was a scavenger.
Scientists have long suspected that the lumbering plant-eating dinosaurs evolved from small fleet-footed predators, but no fossil had ever been found to support this theory. That is why many scientists were excited when Falcarius was discovered earlier this year, because it shared traits common to both groups. Falcarius lived about 125 million years ago and had unwieldy sickle-shaped claws, but short squat legs that would not have been very useful for chasing down prey. It also had the beginnings of a large pot-belly and leaf-shredding teeth.
This tiny animal is one of the reasons why the evolutionary link between birds and dinosaurs is still an issue of debate. It is the oldest animal ever known to have what appears to be feathers, but it was not a dinosaur. Rather, Longisquama was a small reptile, a lizard-sized creature that lived in Central Asia 220 million years ago. It walked on four legs and had feather-like appendages protruding from its spine, which it may have used to glide between trees.
Mei long was a small duck-sized dinosaur that lived about 130 million years ago. In Chinese, its name means "soundly sleeping dragon," a reference to the posture in which it was discovered: curled up with its head tucked under a forelimb. This posture is identical to that used by modern birds while dozing. Scientists think that birds sleep this way to keep warm, and the discovery of Mei long supports the theory that some dinosaurs were warm-blooded like modern birds.
Like Archaeopteryx, Microraptor was about the size of a crow and had teeth, claws and feathers on all four limbs that it may have used to glide between trees. However, it is more closely related to dinosaurs than to birds, and many scientists believe that this 124 million-year-old dinosaur may be the long-sought missing link between the two groups.
Ornithomimus, whose name means "bird-mimic," was an ostrich-like dinosaur that lived approximately 70 million years ago. It was about 10-15 feet long — most of which was taken up by its neck and tail — and had a horny beak, a small head and hollow bones. It was fast and agile, and may have been able to run at speeds of up to 70 mph as fast as a cheetah.
Oviraptor was a small bird-like animal that lived about 80 million years ago. It had long slender legs, squat, strong arms, and a short toothless beak. It also had a small horn-like crest that it probably used for mating displays. Its name in Latin means "egg thief," because the first Oviraptor fossil ever discovered was found near what was thought to be a Protoceratop's nest. However, closer analysis later revealed that the nest contained Oviraptor eggs. This has lead to Oviraptor's image-makeover in recent years from that of an egg snatcher to a nurturing parent.
This raven-sized animal belonged to the same group of dinosaurs as Velociraptor, but it had many bird-like features. Rahonavis lived about 80 million years ago and had a retractable "sickle-claw" on the middle toe of each foot. It had feathered wings like a bird but a long bony tail like Archaeopteryx.
About the size of a sparrow, Sinornis santensis lived about 135 million years ago and was probably an excellent flier that was capable of sustained flight. Itâ€™s slender legs and sharp claws were ill-equipped for walking but it was able to perch and to skitter up and down trees. It was more bird-like than its ancestor Archaeopteryx, but it still had teeth and a short snout instead of a true beak.
Sinornithosaurus was the fifth and most bird-like feathered dinosaur species ever to be discovered. It lived about 125 million years ago and was a dromaeosaurid. Its discovery strongly suggests that other dromaeosaurids may have also had feathers. Some scientists believe that its discovery is proof that feathers first developed in quick-footed, ground-dwelling dinosaurs, instead of those that lived in trees.
Like Micropteryx, Sinosauropteryx was more closely related to dinosaurs than to birds, and yet it clearly had feathers. It was about 3 feet long and lived in China about 125 million years ago. It had long legs, short arms, a long bony tail and it probably ate insects and small animals.
Troodon had one of the largest brain-to-body size ratios of any known dinosaur and it is believed to have been one of the most intelligent dinosaurs that ever lived. Its large, slightly forward facing eyes suggest that it was a nocturnal creature with excellent depth perception and it had long arms that it could fold back like a bird. It lived about 70 million years ago.
Velociraptor is one of the most bird-like dinosaurs ever discovered. It was small and fast, and the sickle-shaped claw on the second toe of each foot made it a formidable predator. A special bone in its wrist allowed it to swivel its wrist sideways in a flapping motion and to fold its arm against its body like a bird. This motion allowed it to snap its arms forward to grab fleeing prey and is an important part of the flight stroke in modern birds.