Not all dinosaurs have obvious similarities to birds, but for those that do, the similarities are not only frightening, but suggest that dinosaurs evolved into modern day birds. While many scientists now support this theory, creationists are pushing hard against it. Either way, the similarities remain, and many are listed below.
Legs and Feet
The legs and feet of bipedal dinosaurs closely resemble that of a bird, three toes forward, one toe back. Some fossilized dinosaur tracks resemble exactly, with the exception of size, the tracks of an Emu. Both dinosaurs and birds have legs with ankles that are about midway up the leg, and our equivalent of a knee, is even higher.
Although some dinosaurs walked on all fours, many stood on their two hind legs. With a small stretch of the imagination we can see a connection between any bipedal dinosaur and an ostrich or emu.
Recent evidence has indicated the the bones of some dinosaurs were hollow, much like those of a bird. These lightweight bones would lend themselves not only to flight, but in dinosaurs were used for breathing purposes too. In order for dinosaurs to grow as big as they did, they needed to process more oxygen, this was done with the help of air sacks in their bones. Birds process more oxygen too, but for the purposes of flying faster, higher, or diving deeper.
Birds and dinosaurs share a unique style of breathing, which is quite the way humans and other animals breathe. Birds have lungs that do not expand and collapse as ours do. One cannot watch a bird breathe as you can watch a cat or dog, by seeing the chest expand and collapse. Instead birds used a system of air sacks to pump air through the lungs. These same features have been indicated on a newly discovered species of dinosaur called Aerosteon riocoloradensis.
It is debatable if the chicken came first, or the egg, except to say that dinosaurs laid eggs long before chickens were even in existance. Many dinosaurs have also been shown to make nests and rear their young. Most birds bring food and feed their young, although not all do. Chickens, for example, do not bring food to their young. It is likely that some dinosaurs fed their young and others did not.
This is the bone at the front of the chest that attaches to the flight muscles in birds. Some dinosaurs have been shown to have a similar shaped sternum.
Some birds, such as the ostrich, emu, and turacos have primitive claws on their wings, these very much resemble the diminutive claws on the front limbs of some dinosaurs, particularly the meat eaters.
Look at the neck of a bird, preferably a larger bird, you will see from the side that the neck is typically "S" shaped. This is similar to that of a dinosaur. Some birds, like some dinosaurs, have longer necks, making this more pronounced than others.
The orbit is the hole in the skull for the eye socket, in both birds, and dinosaurs these holes are relatively large in proportion to the skull itself.
The shape of a pelvis is very telling, while not true of all dinosaurs, some had pelvises shaped like those of a bird. Those with a bird-liked shaped pelvis were of the order Ornithischia.
Powerful Hind Limbs
Undoubtedly many meat eating dinosaurs did not use their feeble forelegs for killing or fighting. Instead they relied on powerful hind legs. The same attribute of having powerful hind legs belongs to birds like ostriches and emus. Their hind limbs are so powerful that a well placed forward strike can disembowel a human.
We all know about the fancy headgear of some dinosaurs. Interestingly enough some birds sport just as much headgear. One such bird is the Cassowary, a strikingly primitive looking bird.
The Archaeopteryx has been preserved to clearly show it had feathers but more recently other dinosaurs have been found to have similar features too. These being "theropods". These feathers were not initially for flight and probably served the purpose of keeping the animals warm, allowing them to be more effective hunters, since with added warmth they could hunt during the cool nights, when the newly developing mammals were active.
Certainly there are some dinosaurs which resemble birds more than others. Equally so there are some birds which resemble dinosaurs more than others. The similarities alone do not prove one descended from the other, but they certainly hint at it.